Mineralogy and Chemistry of Samples From a 

Dri II Hole in the Southern Extension of the 

Land-Pebble Phosphate District, Florida 

-

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Ave. 
Mineralogy and Chemistry of Samples From a 

Dri II Hole in the Southern Extension of the 

Land-Pebble Phosphate District, Florida 

By JAMES B. CATHCART and THEODORE BOTINELLY 

Economics of phosphate mineralogy and 

chemistry in an area of possible future mining 

U.S. GEOLOGICAL SURVEY BULLETIN 1978 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

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purposes only and does not imply endorsement by the U.S. Government. 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1991 

For sale by the 

Books and Open-File Reports Section 

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Library of Congress Cataloging-in-Publication Data 

Cathcart, James Bachelder, 1917-

Mineralogy and chemistry of samples from a: drill hole in the southern 

extension of the Land Pebble Phosphate District, Florida : economics of 

phosphate mineralogy and chemistry in an area of possible future mining I 

by James B. Cathcart and Theodore Botinelly. 

p. cm.-(U.S. Geological Survey bulletin; 1978) 

Includes bibliographical references. 

Supt. of Docs. no.: 119.3:1978 

1. Phosphate rock-Florida. 2. Phosphate minerals-Florida. 

I. Botinelly, Theodore, 1916- . II. Title. Ill. Series. 

QE75.B9 no. 1978 

[QE471.15.P48] 

557.3 s-dc20 

[553.6'4] 91-12934 

CIP 
CONTENTS 

Abstract 1 

Introduction 1 

Structure 2 

Stratigraphy 3 

Eocene 3 

Oligocene 3 

Miocene 4 

Hawthorn Group 4 

Arcadia Formation 4 

Peace River Formation 5 

Bone Valley Formation 5 

Pleistocene and Holocene 8 

Mineralogy 8 

Apatite 8 

Carbonate minerals 9 

Clay minerals 10 

Aluminum phosphate minerals 12 

Pyrite 12 

Micrometeorite (tektite?) 13 

Chemistry 13 

Trace elements 14 

Cadmium 17 

Mercury 19 

Economic geology 19 

Phosphate particles 21 

Bone Valley Formation 21 

Peace River Formation-Upper part 21 

Peace River Formation-Lower part 22 

References cited 23 

FIGURES 

1. Index map of Florida, showing structural features, the land-pebble phosphate 

district and its southern extension, and location of the core hole 2 

2. Diagrammatic cross section through the land-pebble phosphate district and its 

southern extension 3 

3. Graph showing relations of a- and c-cell dimensions of dolomite, ferroan dolomite, 

and ankerite 10 

4. Photographs of calcite crystals 11 

5. Plots of clay-mineral distribution in samples from the core hole 12 

6. Photograph of an iron spherule embedded in a phosphate grain 13 

7. Scatter diagrams showing relations of phosphorus to calcium, fluorine, magnesium, 

sodium, iron, yttrium, lanthanum, and acid-insoluble residue 16 

8. Plots of the distribution of elements in the core samples 17 

9. Scatter diagrams showing relations of trace metals in the core samples 18 

Contents Ill 
10. Scatter diagram showing relations of cadmium and zinc in the concentrate 

fraction of the core samples 19 

11. Distribution of minerals (except clay) and weight percent of the minus-150-

mesh fraction of the core samples 20 

12-18. Photographs of: 

12. Phosphate grains (+1-mm fraction), sample 1-87 21 

13. Phosphate concentrate fraction, sample F3-87 21 

14. Phosphate grains from samples F6-87 and F7-87 22 

15. Gray-brown phosphate grain from sample F14--87 22 

16. Phosphate grains (-1 mm +0.1 mm), samples F8-87 and Fl0-87 23 

17. Phosphate grains (+1 mm), samples F14--87 and F16-87 23 

18. Phosphate feed fraction (-1 mm +0.1 mm), samples F14--87 and 

F18-87 24 

19. Plots of the ratios of coarse to fine phosphate grains 24 

TABLES 

1. General stratigraphic relations in the land-pebble phosphate district and its 

southern extension 4 

2. Lithologic log of core hole 6 

3. Comparisons of francolite a-cell dimensions 9 

4. Comparisons of unit-cell dimensions and unit-cell volumes of dolomite 10 

5. Chemical analyses of dolomite 10 

6. Chemical analyses of the minus 1-mm plus 0.1-mm fraction of core samples 13 

7. Trace-element content of phosphate samples 14 

8. Cadmium, zinc, mercury, and uranium contents of apatite concentrate fractions of 

phosphate samples 15 

IV Contents 
Mineralogy and Chemistry of Samples From a 

Drill Hole in the Southern Extension of the 

Land-Pebble Phosphate District, Florida 

By James B. Cathcart and Theodore Botinelly 

Abstract 

Although there are abundant data on the phosphate 

deposits of the land-pebble district of Florida (in Polk and 

Hillsborough Counties), data on the deposits of its southern 

extension (in Hardee, Manatee, and DeSoto Counties) are 

scarce. A core hole in the southern extension (in southern 

Hardee County) penetrated 5 ft (feet) of the Bone Valley 

Formation and about 90 ft of phosphorite of the Peace River 

Formation, both of the Miocene and Pliocene Hawthorn 

Group. 

The apatite mineral of the Bone Valley and the Peace 

River Formations is carbonate fluorapatite (francolite), but 

there are distinct differences in francolite composition that are 

indicated by variations in the a-cell dimensions. The average 

a-cell dimension of the francolite in samples of the Bone 

Valley Formation is 9.345 A (angstroms), but it is only 9.327 A 

in samples from the Peace River Formation. Francolites with 

a-cell dimensions of less than 9.30 A are considered to be 

highly substituted. The highly substituted francolites contain 

more MgO, Na2 0, and C02 , and therefore have a lower P 2 0 5 

content than the less substituted francolite. The economic 

implications are clear: phosphate products from the southern 

extension will be low in P20 5 and high (>0.5 percent) in MgO. 

Dolomite is the principal carbonate mineral, although 

some calcite in the form of "rice-grain" scalenohedrons is in 

the lower part of the Peace River Formation. The dolomite in 

the deeper part of the core hole is very close to ferroan 

dolomite, whereas the altered dolomite at the base of the 

mining pits in the land-pebble district is a nonferrous dolomite. 

This difference indicates that the primary dolomite of the 

deposits was iron rich, and the dolomites of the mine pits have 

been altered and iron removed. 

Clay minerals of the Peace River Formation include 

palygorskite, sepiolite, and montmorillonite, whereas the clay 

mineral of the Bone Valley Formation is montmorillonite, and 

in the highly altered surficial parts ofthe Bone Valley, kaolinite 

is the predominant clay mineral. 

Manuscript approved for publication February 22, 1991. 

Data on trace elements are still being collected, but data 

on mercury and cadmium are complete. Mercury and cadmium, both toxic elements, are present in the phosphate 

products in both the Bone Valley Formation and Hawthorn 

Group but in amounts that range from 0.02 to 0.63 ppm (parts 

per million) (Hg) and from 2 to 15 ppm (Cd), too low to be of 

concern. The data show that the relations of zinc and cadmium 

in these samples is positive and the correlation is strong, and it 

seems likely that the cadmium is allied with zinc in sphalerite. 

A small sphere (0.1 mm, millimeter) was found 

imbedded in a phosphate grain 90ft below the surface. X-ray 

data show that the grain is composed mainly of native iron. 

Thus, this grain may be a micrometeorite (tektite?), the first 

found in Miocene phosphorite deposits. 

INTRODUCTION 

The land-pebble phosphate district in central Florida 

is the most productive phosphate district in the world. About 

1.1 billion metric tons of phosphate rock containing an 

average of about 32 percent P20 5 have been produced since 

mining began in 1891. Almost all of the production has 

come from Polk and Hillsborough Counties, although there 

has been some mining in the northern parts of Hardee and 

Manatee Counties (fig. 1). 

The areal extent of the land-pebble district has been 

known, in general, for many years. Eldridge (1893, p. 197) 

published a map that showed the land-pebble district in Polk 

and Hillsborough Counties, and Mansfield published a map 

of the phosphate deposits of Florida ( 1942, pl. 5) that 

showed a high-grade pebble area (equivalent to the landpebble phosphate district) in Polk and Hillsborough Counties and a low-grade area that included much of Manatee 

and Hardee Counties and extended south into Sarasota and 

DeSoto Counties. This was the first map that indicated the 

presence of potentially economic phosphate to the south of 

the classic land-pebble district. This area was named the 

Introduction 
EXPLANATION 

A Location of 

""'- cross section ""'-A' (figure 2) 

Land-pebble 

phosphate 

district 

r----.. Southern 

' ,' extension 

, of land-pebble 

' phosphate district 

• Core-hole 

84' 82' 

I 

GEORGIA 

- - - FLORIDA-:;:: - 1 • ASR Tallahassee 

--

location 28''-----t---t--GJ-~'-f----'1------"r----+----+---t-

- - Boundary of 

structural feature 

X' Mine 

SA, Suwannee River 

SC, Saddle Creek 

HP, Hooker's Prairie 

L, Lonesome 

HC, Hardee Complex 

50 100 MILES 

II I I II 

100 

83'' 82' 

I 1 I 

1-\ 

\ 

\.~ 

\ 

\ 

Polk) -~-----

I 

40 MILES 

I 

40 KILOMETERS 

Figure 1. Index map of Florida, showing structural features, the land-pebble phosphate district and its southern extension, and 

location of the core hole. 

"southern extension" of the land-pebble district by Bernardi 

and Hall ( 1980), who pointed out that the phosphate rock in 

the southern extension differs from the rock in the landpebble district in that it contains less P20 5 and more MgO. 

Additional differences in the economic geology of the two 

areas were discussed by Cathcart (1985), but details of the 

mineralogy and chemistry of the phosphate rock in the 

southern extension have not been published. 

Core from a drill hole in Hardee County in the 

northern part of the southern extension was provided for this 

study by John Paugh, Chief Geologist of Gardinier, Inc. The 

hole was drilled in sec. 7, T. 34 S., R. 24 E. The core was 

logged and sampled, the samples were screened, and the 

pebble ( + 1 mm), concentrate ( -1 mm, +0.1 mm), and slime 

( -0.1 mm) fractions of each sample were analyzed by X-ray 

diffraction. Chemical analyses were made by D.L. Fey, 

P.L. Hageman, T.A. Roemer, and J.D. Sharkey, and semiquantitative spectrographic analyses were made by B.M. 

Adrian and S.J. Sutley, all of the Denver laboratories of the 

U.S. Geological Survey. 

STRUCTURE 

Peninsular Florida is in the Atlantic Coastal Plain and 

consists of Tertiary sediments that dip very gently (1 0-

20ft/mile) away from the major structural features. 

The Ocala uplift (also called the Ocala arch or Ocala 

high) dominates the structure of the Florida peninsula. The 

uplift was a positive feature during the Miocene (Vernon, 

1951; Olson, 1966), and Miocene sediments are thinned on 

the uplift and were removed from the crest of the uplift by 

subsequent erosion, so that Pleistocene and Holocene 

sediments directly overlie rocks of Eocene and Oligocene 

age. Similarly, Miocene sediments are not present on the 

Sanford high (fig. 1). 

Rocks of Miocene age dip gently and thicken away 

from the highs. In the Jacksonville basin and the south 

Florida embayment (fig. 1), Miocene and post-Miocene 

rocks are much thicker than rocks of equivalent ages on the 

platforms. 

The phosphate sediments of the Bone Valley Formation in the land-pebble district were deposited in a shallow 

basin on the south flank of the Ocala uplift. The basin was 

defined by both structural and topographic features on the 

north, west, and east, but was open to the sea to the south. 

Southward thickening of Miocene and post-Miocene 

sediments from the land-pebble district into the south 

Florida embayment is clearly shown on the cross section 

(fig. 2). 

Regional geologic structure is important in the distribution and physical characteristics of the phosphate 

deposits. Coarse phosphate of the land-pebble district was 

deposited in the shallow basin at the edge of the sea during 

Miocene and Pliocene time. Carbonate rock, phosphatized 

during an initial regression, was broken up, rolled and 

rounded, and deposited during transgression as beach 

gravel, forming the basal conglomerate of the Bone Valley 

Formation. Fine-grained phosphate pellets, quartz sand, and 

clay were deposited further offshore. This lateral facies 

2 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
A I c.....lll(._ ___ Land-pebble phosphate district -----~~•~1 ...... 11(1-------- Southern extension ------.lJ>-~ A, I ~ Q) 8:g 

Tbl 

--? 

Tp 

. ---

EXPLANATION - -? 

--? ·--

Qt Surficial sand and swamp deposits, undifferentiated 

(Holocene and Pliocene) 

Projection of drill hole · ..____ 

into the plane of the 

section Tt 

Tbv 

Tamiami Formation (Pliocene and Miocene) 

Bone Valley Formation of the Hawthorn Group 

(Pliocene and Miocene)--Upper sand 

Tbl Bone Valley Formation of the Hawthorn Group 

(Miocene )--Lower phosphorite 

Tp Peace River Formation of the Hawthorn Group 

(Miocene) 

Ta 

Tat 

Ts 

To 

Arcadia Formation of the Hawthorn Group (Miocene) 

Tampa Member of the Arcadia Formation (Miocene) 

Suwannee Limestone (Oligocene) 

Ocala Group (Eocene) 

Contact--Queried and dashed where uncertain 

Figure 2. Diagrammatic cross section through the land-pebble phosphate district and its southern extension, Florida. Location 

of section shown on figure 1. 

change was also repeated vertically, as the sea transgressed, 

so that conglomeratic phosphate is overlain by sandy 

phosphorite and in tum is overlain by more clayey 

phosphate material. 

Deposits in the southern extension are thicker and are 

finer grained than are the deposits of the land-pebble 

district. Conglomeratic phosphate deposits (pebble beds) 

are not present except in the northernmost part of the 

southern extension, and the Bone Valley Formation is 

present only as outliers in the southern extension. 

STRATIGRAPHY 

The surface of the land-pebble phosphate district is 

blanketed by unconsolidated sand and swamp deposits of 

Pleistocene and Holocene age. The only exposures of 

pre-Pleistocene sediments are in mining pits and where the 

Alafia and Peace Rivers are flowing on carbonate rock that 

is exposed at times of low water. 

The oldest rock exposed in the mining pits is 

carbonate rock of the Hawthorn Group. Mining stops at this 

material that represents about the middle Miocene. Older 

rocks in the district and its southern extension are known 

only from a few deep drill holes. 

The phosphate deposits are confined to rocks of 

Miocene age and to younger sediments containing phosphate derived from the Miocene rocks. The discussion of 

stratigraphy, therefore, is concentrated on these rocks, and 

older rocks, known only from drill holes, are discussed 

briefly. General stratigraphic relations are shown on table 1. 

Eocene 

Ocala Group.-Limestone of the Eocene Ocala 

Group underlies all of Peninsular Florida. The limestone is 

white to cream, fossiliferous, and "***in places contains as 

little as four-tenths of one percent of impurities" (Cooke, 

1945, p. 54). 

Oligocene 

Suwannee Limestone.-The Suwannee Limestone 

consists predominantly of calcium carbonate but contains as 

much as 10 percent quartz and chert. Drill-hole data show 

that the Suwannee is present in the northernmost and 

western parts of the land-pebble district. The Suwannee is 

missing over much of the rest of the district and its southern 

extension where rocks of Miocene age rest directly on rocks 

of the Ocala Group (fig. 2). 

Stratigraphy 3 
Table 1. General stratigraphic relations in the land-pebble phosphate district and its southern extension, Florida 

Land-pebble district Southern extension 

HOLOCENE Sand and swamp deposits 

(2-6ft; 1-2 m) 

Bedded clayey sand. Channel deposits of Bedded slightly clayey sand. 

PLEISTOCENE pebble phosphate. {20-70 ft; 6-20 m) 

(1 0-40 ft; 3-12 m) 

•W 

>-z Oz Clayey sand. Trace of phosphate, aluminum Clayey sand, abundant shell, ~<(z 

....JW ~0 and iron phosphate when leached. trace of phosphate . ~~0 

C..() _J- (0-30 ft; 0-12 m) (0-75 ft; 0-23 m) ~a:- <( ..... <(0 ..... ><( .,_u.. w~ 

za:: Phosphorite, sandy, clayey, pebbly. Abundant 

a_ 

oo aluminum phosphate where leached. r:oLL (0-50 ft; 0-15 m) 

=> 

0 a::z Clay and sand, dolomitic. Abundant Clay, sandy, silty, contains dolomite as lenses 

a: 

>-

wo phosphate, in part residual from underlying and fine silt to clay-size rhombs. Abundant 

(9 - ..... carbonate rock. Ranges from 1 0 ft (3 m) fine-grained phosphate pellets. 

w a:<( 

w~ at the north edge of the district to 60 ft {60-150 ft; 18-45 m) 

z z Oa:: (18 m) at the south. Thin beds of 

w a: <eo Wu.. fossiliferous dolomite are more abundant 

() 0 a.. toward base. 

0 I z - r- <CO Dolomite, sandy, contains abundant phosphate Dolomite, sandy, fossiliferous. Some calcite, 

~ $ oi= pellets and some pebble. Thickness more abundant at depth, fine-grained <(<( ranges from 10ft (3 m) in the north to phosphate pellets throughout. Clastic 0~ <( a:: a: 1 00 ft (30 m) at the boundary with the interbeds are more abundant near top. 

I <CO southern extension. Interbeds of dolosilt {100-150 ft; 30-45 m) u.. and doloclay are present, particularly at 

<(a: ~ the top. 

a_W 

~Ill 

<(~ Sandy clay. Chert, carbonate, some phosphate . ._w ~ {0-20 ft; 0-6 m) (1 0-50 ft; 3-15m) 

OLIGOCENE SUWANNEE LIMESTONE 

EOCENE 

Miocene 

The Miocene of Peninsular Florida was divided into 

three parts (Cooke, 1945, p. 109)-the Tampa Limestone at 

the base, the Hawthorn Formation in the middle, and the 

Duplin Marl and equivalents at the top. Data from drill holes 

and mine pits in the land-pebble district indicated that the 

Hawthorn Formation could be divided into a lower 

carbonate unit and an upper siliciclastic unit (Cathcart, 

1985). Scott ( 1988) proposed that the Hawthorn be raised to 

group status and that the group include all of the Miocene. 

He proposed the name "Arcadia Formation" for the lower 

carbonate-rich part of the Hawthorn (about equivalent to the 

informal lower carbonate unit) but included the Tampa as a 

member at the base of the Arcadia Formation. The Peace 

OCALA GROUP 

River Formation was proposed as a formal name for the 

predominantly clastic upper part of the Hawthorn (about 

equivalent. to the upper clastic unit). 

Hawthorn Group 

Arcadia Formation 

The Arcadia Formation consists primarily of sandy, 

gray to white fossiliferous dolomite with interbeds of 

gray-green dolomitic, sandy, and silty clay. All lithologic 

units contain varying amounts of phosphate grains. The 

Arcadia Formation ranges from a feather edge at the 

northern limit of the land-pebble district to about 100 ft at 

4 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
the southern limit of the district. The formation thickens to 

the south and is about 150ft thick in the southern part of 

DeSoto County. 

The Arcadia Formation in the southern extension is 

similar lithologically to the formation in the land-pebble 

district, except that the formation contains some limestone 

beds near its base in southern DeSoto County. 

Sample F18-87 from the core hole (121-124 ft below 

the surface) consists of white, sandy phosphatic dolomite 

(table 2) that is assigned to the Arcadia Formation. The 

lithology of this sample is typical of the carbonate rock of 

the Arcadia Formation, and the thickness (3 ft) is greater 

than the average thickness (0.5-1 ft) of the carbonate lenses 

in the Peace River Formation. 

Phosphatic carbonate rock of the Hawthorn Group 

thickens markedly in southern Florida. For example, oil 

tests in Dade County have penetrated as much as 600 ft of 

the Hawthorn Group. Most of the thickness seems to be in 

the Arcadia Formation. Cuttings were reported as limestone 

or dolomite, but recovery of samples was poor and 

incomplete. 

Tampa Member.-The Tampa Member of the Arcadia Formation in the land-pebble district consists of calcareous clayey sand and carbonate rock that contains some 

chert and minor phosphate nodules and pellets. The Tampa 

Member is present in the northernmost part and to the west 

of the land-pebble district, where it is as much as 10 ft in 

thickness (fig. 2). The Tampa Member is missing over much 

of the rest of the land-pebble district but is present in the 

southern extension where it is as much as 50 ft thick. In the 

southern extension, the Tampa Member consists of sandy 

clay and carbonate rock that contain some phosphate grains 

and chert fragments. The core hole that was investigated for 

this paper did not reach the Tampa Member. 

Peace River Formation 

The Peace River Formation of the Hawthorn Group 

(Scott, 1988) is about equivalent to the informal upper 

clastic unit of the Hawthorn (Cathcart, 1985). The unit is 

predominantly clastic and consists of gray-green to lightgray (white when dry) dolomitic clayey and silty sand to 

sandy and silty clay, and thin lenticular beds of hard 

dolomite. All of the beds contain black, brown, and gray 

phosphate pellets and nodules (pebbles). The Peace River 

Formation is thin or absent in the northern part of the 

land-pebble district, and clastic rock (called "bedclay") may 

be residual from the underlying carbonate rock, and, 

therefore, a part of the Arcadia Formation. In the southern 

part of the land-pebble district, the Peace River Formation 

thickens to as much as 50 ft and contains thin dolomite beds 

that are more abundant with depth. Thus the contact of the 

Peace River and Arcadia Formations is difficult to locate 

precisely. The Arcadia Formation differs from the Peace 

River only in that it has much more abundant carbonate 

rock. 

The Peace River Formation thickens markedly in the 

southern extension of the land-pebble district (fig. 2), and is 

as much as 150 ft thick in southern De Soto County. The 

formation is lithologically identical to the formation in the 

land-pebble district except that it contains less of the pebble 

fraction, and the concentrate fraction tends to contain more 

very fine grained phosphate pellets. All of the potentially 

economic phosphate in the southern extension is in the 

Peace River Formation. 

Bone Valley Formation 

The earliest publications on the phosphate deposits of 

the land-pebble district did not formally name the 

phosphate-bearing formation. Dall (1892) simply called 

them "pebble phosphates" and considered them to be of 

Pliocene age, while Eldridge (1893) referred to them as 

"land-pebble phosphate." The first use of the name "Bone 

Valley" was by Matson and Clapp (1909, p. 138) who 

designated the pebble phosphate deposits then being mined 

as Bone Valley Gravel. They described the deposits as being 

largely fluviatile in origin and probably of Pliocene age. 

Matson (1915, p. 20) was the first to indicate that the Bone 

Valley might be of Miocene age, although he pointed out 

that it has "***generally been regarded as Pliocene and it is 

so classified here***". 

Cooke (1945, p. 203) discarded the term "gravel" in 

favor of the more general term "Bone Valley Formation" for 

the phosphate deposits, because by that time, only a small 

part of the deposit was gravel-most of what was being 

mined was sand-size material. He considered the formation 

to be of Pliocene age. 

Vertebrate fossils in the Bone Valley Formation are 

now thought to be of late Miocene age (Webb and Crissinger, 1983), although the uppermost part of the formation 

may be of Pliocene age. Scott (1988) included the Bone 

Valley as a member in the uppermost part of the Peace 

River Formation of the Hawthorn Group, but we think that 

the Bone Valley should be designated as a formation in the 

uppermost part of the Hawthorn Group, overlying the Peace 

River Formation. 

The Bone Valley Formation was informally divided 

into a lower phosphorite unit and an upper clayey sand unit 

(Cathcart, 1963). The lower unit in the land-pebble district 

is a brown, gray, and white sandy and clayey phosphorite 

that commonly has a basal conglomerate composed of 

phosphate cobbles and boulders that are almost all phosphatized carbonate rock. The phosphate conglomerate was 

formed by the phosphatization of carbonate rock of the 

Peace River or Arcadia Formations that was reworked and 

concentrated at the base of the Bone Valley. The coarse 

phosphate rock in the land-pebble district is concentrated on 

topographic highs (ridges) that formed prior to the 

deposition of the Bone Valley. Submarine winnowing 

removed sand-size phosphate and quartz particles and the 

Stratigraphy 5 
Table 2. Lithologic log of core hole studied, Hardee County, Fla. 

[Core hole is in sec. 7, T. 34 S., R. 24 E.; n.s., no sample] 

Depth in feet 

below surface 

0-2 

2-15 

16-25 

25-29 

29-29.5 

29.5-30 

30-38 

38-44.5 

44.5-53.5 

53.5-57 

57-69 

Sample no. 

n.s. 

n.s. 

n.s. 

F1-87 

F2-87 

F3-87 

F4-87 

F5-87 

F6-87 

F7-87 

F8-87 

Lithology 

Holocene 

Sand, dark-gray to black, organic. Surface soil. 

Pleistocene 

Sand, tan, unconsolidated. Very slightly clayey at base. 

Sand, gray-tan, slightly clayey. 

Miocene-Pliocene 

Bone Valley Formation of the Hawthorn Group-Upper part 

Sand, gray-tan, slightly clayey. Minor (less than 5 percent) dull-white leached phosphate grains. 

Trace of shiny white and tan grains. Some phosphatized shell fragments, trace of fish and shark 

teeth. Trace of shiny black and brown fine-grained phosphate pellets. A few fragments of tan sand 

cemented by aluminum phosphate minerals and apatite. Gray clay clasts in base, derived from clay 

below. 

Miocene 

Bone Valley Formation of the Hawthorn Group-Lower part 

Clay, gray, silty. Thin laminae of white sand that contain small amounts of white and tan shiny 

phosphate pellets. 

Sand, gray, slightly clayey. Contains abundant brown, gray, black, white, and cream phosphate 

grains, phosphatized rock fragments, and phosphatized fossils. Many of the coarser grains are 

broken and rerounded. The sample has a higher percentage of coarse than fine phosphate. 

Peace River Formation of the Hawthorn Group 

Sand, yellow-gray-green, slightly clayey. Abundant brown, tan, gray, and some black phosphate 

pebbles, phosphatized rock fragments, and phosphatized fossils. Fine-grained phosphate is much 

greater in amount than coarse grained. Fine phosphate is shiny and brown, gray, tan, black, and 

white. Includes subangular translucent amber fragments of phosphatized shell material. Trace of 

white dolomite fragments. 

Note: The phosphate grains in the samples from 30 to 53ft are predominantly light-colored-gray, 

tan, white, cream, and only about 5-10 percent black and dark-brown grains, in sharp contrast to 

the samples from 53 ft to the base of the hole. 

Sand, gray-green, contains abundant thin green irregular and lenticular clay laminae. Most of the 

clay in the sample is in these laminae. Contains minor tan and cream-gray, and some black 

phosphate pebbles, phosphatized rock fragments, and phosphatized fossil fragments. Fine 

phosphate (concentrate) is much more abundant than coarse and is tan, light and dark brown, gray 

brown, greenish brown, white, cream, and black. All grains are shiny and are subspherical or rod 

shaped. Some phosphatized fossils. Trace of dolomite. 

Sand, yellow-gray-green, slightly clayey. Base sample interval is 0.5-ft green-gray clay bed. Trace 

of phosphate pebbles; brown, gray, green, white, and a trace of black. Some shark teeth. 

Concentrate size much more abundant than pebble size. Phosphate pellets, some fish teeth: brown, 

tan, gray-green, some black and white. Trace of white dolomite fragments. 

Dolomite, yellow-white, sandy, soft (or doloclay). Contains abundant phosphate grains, mostly 

concentrate size but with some pebble. Phosphate is black, brown, gray, and tan pellets, some 

phosphatized rock fragments (dolomite?), and phosphatized fossils. Black and dark-brown 

phosphate grains are about 70-80 percent of the total. Some quartz sand. 

Sand, gray and gray-green, clayey. Clay fraction is dolomitic. Some white, soft dolomite fragments. 

Phosphate (pebble and concentrate) is predominantly black and brown, very shiny, round pellets, 

some phosphatized rock fragments. Trace of shark teeth, and fossil molds. A few gray-green and 

red-brown phosphate pellets, some tan and white. 

6 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Table 2. Lithologic log of core hole studied, Hardee County, Fla.-Continued 

[Core hole is in sec. 7, T. 34 S., R. 24 E.; n.s., no sample] 

Depth in feet 

below surface 

69-73.5 

73.5-82 

82-87 

87-95 

95-100 

100-104 

104-108 

108-114 

114-121 

Sample No. 

F9-87 

FI0-87 

Fll-87 

Fl2-87 

Fl3-87 

Fl4-87 

F15-87 

F16-87 

Fl7-87 

Lithology 

Sand, gray-green, clayey, dolomitic. Contains predominantly black and brown phosphate pellets and 

gray and white phosphatized dolomite rock fragments. Some compound pebbles. Some white 

dolomite fragments. Phosphatized fossil molds. Concentrate much more abundant than pebble. 

Sand, dark-gray-green, clayey, dolomitic. Grades downward into dolomite of sample Fll-87. 

Concentrate-size phosphate pellets much more abundant than pebble size. Pellets are black and 

brown with lesser amounts of dark gray and green. Pellets are highly polished. Some phosphatized 

fossils, including shark teeth. A few white dolomite fragments more abundant with depth. 

Dolomite, yellow-white, sandy, soft (or doloclay). Interbedded with dark-gray phosphate and quartz 

sand. Coarse fraction (pebble) consists of dolomite fragments, partly phosphatized dolomite 

fragments, and shiny black and some gray phosphate grains. Fine phosphate (concentrate) is more 

abundant than the pebble and is predominantly black with some gray, tan, and brown very shiny 

grains. Some broken and rerounded shark teeth. 

Sand, dark-gray-green, clayey. Coarse fraction consists of cream-white phosphatic dolomite 

fragments and black, gray, and brown polished phosphate grains. One compound pebble contained 

a metallic sphere (about 0.1 mm) embedded in it. X-ray showed that the sphere was largely 

elemental iron. This may be a micrometeorite (tektite?). Concentrate-size phosphate is black with 

some brown and gray shiny pellets. Thin (0.5 in.) lenses of dolomite at 89.5 and 94.5 ft. 

Clay, dark-gray-green, silty, dolomitic. Irregular areas (boring fillings or bioturbation) of black 

phosphate and quartz sand. Contains yellow crystals (scalenohedrons) of calcite (rice-grain 

crystals). Fine phosphate is more abundant than coarse. Almost 80 percent of the phosphate grains 

are black, very shiny, structureless pellets, but there are some phosphatized rock fragments and 

phosphatized fossil molds. 

Note: Samples F13-87 through F17-87 contain rice-grain crystals of calcite in trace to moderate 

amounts. 

Sand, dark-gray-green, clayey. Pebble fraction consists of black and some brown and gray pebbles 

and phosphatized rock fragments, some of which are broken and rerounded, and abundant calcite 

scalenohedrons. Concentrate-size phosphate is more abundant and is black with some brown and 

gray shiny pellets and minor amounts of fossils and rock fragments. 

Miocene 

Sand, gray-green and white mottled, clayey, dolomitic. More clayey at base. Phosphate pebble is not 

abundant and is black with some brown and gray, some phosphatized rock fragments and 

phosphatized fossils (molds and teeth). Concentrate-size phosphate is predominantly black and 

more abundant than the pebble. Clay fraction is dolomitic. 

(Cuttings). Sand, light-gray-green, clayey, dolomitic, with light-gray silty doloclay lenses. Pebble 

fraction is black, gray, brown, and tan smooth, shiny pebbles, some phosphatized rock and 

phosphatized fossils. Some rice-grain calcite crystals. Concentrate fraction is mostly black with 

some brown, shiny phosphate pellets and is more abundant than the pebble. 

Sand, light-gray-green, clayey, dolomitic. Grades down into hard dolomite. Greenish-gray clay 

lenticles throughout interval. White dolomite fragments at base. Black, gray, and brown phosphate 

pellets and phosphatized rock fragments. Concentrate more abundant than pebble size. A few 

phosphatized fossils. 

Arcadia Formation of the Hawthorn Group 

121-124 Fl8-87 Dolomite, white, sandy, phosphatic. Irregular areas of black phosphate and quartz sand. Phosphate 

is mostly black with some dark gray and brown. Concentrate fraction more abundant than pebble. 

Hole bottomed at 124-ft depth in hard dolomite. 

Stratigraphy 7 
clay fraction, thus concentrating the coarse phosphate. Fine 

phosphate and quartz particles were deposited on the flanks 

of the ridges and on the flatlands adjacent to the ridges. 

Pebble-size phosphate is not abundant in the southern 

extension, and the very coarse phosphate boulders characteristic of the Bone Valley in the land-pebble district are not 

present in the southern extension. The Bone Valley in the 

land-pebble district is as much as 50 ft thick and is thickest 

in sinkhole fillings. In the southern extension, the Bone 

Valley is thin (as much as 10 ft) and is missing over much 

of the area. 

The upper unit of the Bone Valley is a clayey sand 

that contains minor to trace amounts of phosphate, most of 

which is present in the basal 1 or 2 ft of the unit. The unit 

is as much as 30 ft thick in the land-pebble district and 

extends as a transgressive unit to the north of the district 

(fig. 2). In the southern extension, the upper unit is present, 

but little is known of its thickness and extent. Data from a 

drill hole in De Soto County showed that the Bone Valley 

Formation was missing and in its place is a clayey, shelly 

sand, the Tamiami Formation (fig. 2). 

Pleistocene and Holocene 

Unconsolidated sediments of Pleistocene and Holocene age gradationally overlie the Bone Valley Formation in 

the land-pebble district and the northern part of the southern 

extension. To the south, in the southern extension, where the 

Bone Valley is not present, Pleistocene sediments overlie 

the Peace River Formation or the Tamiami Formation 

(fig. 2). The cross section (fig. 2) also shows the thickening 

of these sediments to the south, from about 10 ft in the 

northern part of the land-pebble district to as much as 70 ft 

at a drill hole in DeSoto County. 

Pleistocene sediments are unconsolidated sand or 

clayey sand that may have trace amounts of phosphate 

reworked from underlying Bone Valley or Peace River 

Formations. In the land-pebble district, lenticular channel 

deposits of coarse phosphate pebble and sand are present in 

the Pleistocene sediments and are most common at the base 

of the Pleistocene where they directly overlie the lower 

phosphorite unit of the Bone Valley. Vertebrate fossils in 

the channel deposits are of Pleistocene age. 

Surficial deposits of wind-blown sand and swamp 

muck overlie the sand of Pleistocene age and are of 

Holocene age. Except for the swamp muck, these deposits 

have not been separated from the Pleistocene, and the 

surficial sand deposits are lumped as Pleistocene and 

Holocene age. 

MINERALOGY 

Apatite 

The apatite mineral of the phosphate deposits of 

Florida is carbonate fluorapatite (francolite). Detailed work 

by scientists of the Tennessee Valley Authority and the 

International Fertilizer Development Center (Lehr and 

others, 1968; McClellan and Lehr, 1969; McClellan, 1980; 

Van Kauwenbergh and McClellan, 1985) has shown that 

carbonate substitutes for phosphate in a 1: 1 ratio and that 

the maximum amount of substitution is slightly less than 6 

percent by weight (expressed as C02). Both Na+ and Mg2+ 

are present in the francolite structure replacing Ca2

+. 

According to McClellan (1980), maximum MgO in the 

most highly substituted francolite is about 0.6 percent, 

whereas Na20 may be as much as 1.1 percent. Because of 

these substitutions, the P20 5 content of the most highly 

substituted francolite is about 35 percent, whereas fluorapatite contains about 42 percent P20 5• 

The changes in composition of the apatite have 

important implications economically. In addition to lower 

P20 5 content, the higher MgO and Na20 contents can be 

deleterious in the manufacture of phosphate fertilizers. The 

contents of both C02 and MgO in the apatite are difficult to 

measure because of admixtures of calcite and dolomite in 

the phosphate particles. McClellan (1980) showed that the 

dimension of the unit cell can be used to indicate the amount 

of substitution. Therefore, we calculated the a-cell 

dimensions from X-ray diffractograms for all phosphate 

samples from the drill hole (table 3). The data clearly show 

that the samples of weathered (altered) apatite from the 

Bone Valley Formation have distinctly higher a-cell 

dimensions than the apatite from the Peace River 

Formation, which is progressively less altered toward the 

bottom of the core hole. 

Data from Van Kauwenbergh and others (1990) show 

that the apatites of the Peace River Formation have slightly 

lower a-cell dimensions than the samples from the Bone 

Valley. The a-cell dimensions of the apatite from the Bone 

Valley Formation as reported by Van Kauwenbergh and 

others ( 1990) are almost identical with the a-cell 

dimensions for the Bone Valley from this study (9 .343 A 

and 9.345 A, respectively). However, the apatites in the 

samples from the Peace River Formation reported in this 

paper (table 3) have distinctly smaller a-cell dimensions 

than the a-cell dimensions reported by Van Kauwenbergh 

and others (9.327 A for the core samples and 9.338 A for the 

mine samples). It should be noted that the samples of the 

Peace River Formation used in the Van Kauwenbergh study 

were all taken from the mine pits in the land-pebble district 

and are almost certainly altered, whereas the samples from 

deeper in the core hole do not appear to have been altered. 

Van Kauwenbergh and others (1990) shows (table 8) 

a-cell dimensions for less altered apatites from deposits 

around the world. Their data show that the a-cell 

dimensions of North Carolina apatite average 9.323 A (their 

table 8), and are only slightly lower than the a-cell 

dimensions of apatite from the Peace River Formation. The 

apatite from North Carolina is one of the most highly 

8 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Table 3. Francolite a-cell dimensions from the core hole of this 

study compared with data from the literature and from samples of 

phosphorite from North Carolina 

a-cell dimensions (A) 

Location Range Average 

Florida (land-pebble district) 1

: 

Bone Valley Formation 

(22 samples). 9.327-9.368 9.343 

Peace River Formation 

(24 samples). 9.328-9.357 9.338 

Florida (southern extension)2 : 

Bone Valley Formation 

(3 samples). 9.334-9.381 9.345 

Peace River Formation 

(15 samples). 9.300-9.342 9.327 

North Carolina3

: 

Pungo River Formation 

(18 samples). 9.318-9.332 9.323 

North Carolina4 (Pungo River Formation): 

+ 20 mesh (39 samples) 9.298-9.339 9.322 

-20+200 mesh (34 samptes) 9.300-9.334 9.320 

1 Van Kauwenbergh and others (1990, table 7). 2

Data from core hole, this report. 3V an Kauwenbergh and others (1990, table 8). 4

J.B. Cathcart (unpub. data, 1975-90). 

substituted carbonate fluorapatites known in the world 

today. 

These data clearly indicate that the apatite of the 

deeper, relatively unaltered part of the Peace River 

Formation in the southern extension, as shown in this core 

hole, is highly substituted and therefore is low in P20 5 

content and high in C02, MgO, and Na20. 

Carbonate Minerals 

Dolomite.-Dolomite is the most abundant carbonate 

mineral in the phosphate deposits of Florida. Soft, yellow, 

sandy, clayey phosphatic dolomite is present at the base of 

the mining pits in the land-pebble phosphate district. This is 

the so-called bedrock of the district, and samples of this 

dolomite were determined to be slightly deficient in MgO 

by Van Kauwenburgh and others (1990). 

Dolomite is present in trace to minor amounts in 

analyzed samples from the core hole from 30 to 53 ft and is 

a major constituent from 53 ft to 124 ft. The core hole 

bottomed on hard white to gray, sandy, phosphatic 

dolomite. Gray and gray-green dolosilt and doloclay and 

thin lenses of hard white dolomite are present between 53 

and 121 ft. The minus-150-mesh fractions of samples from 

53 ft to the bottom of the core hole (samples F7-F18) 

contain major amounts of dolomite, and all the X-ray peaks 

reported for dolomite were found. The X-ray diffractograms 

of these samples are similar, and the patterns of the dolomite 

differ only slightly from samples of dolomite taken from the 

base of the mining pits. Because the differences were so 

slight, it was decided to calculate the a- and c-cell 

dimensions for the dolomite samples from this core hole and 

compare them with data from the literature (table 4). 

All of the samples fall between pure dolomite and 

ferroan dolomite (table 4) (Howie and Broadhurst, 1958), 

but are closer to ferroan dolomite. Cell dimensions from 

mine-pit samples (Van Kauwenburgh and others, 1990) are 

closer to pure dolomite than are the samples from the core 

hole. These data (fig. 3) clearly show the separation of the 

plots of the core-hole samples from the mine samples. The 

samples from the top of the core hole (F7-87 and F8-87) 

plot between the mine samples and the deeper core samples 

(F10-87, F12-87, F16--87, and F18-87, fig. 3). The deeper 

core samples have not been significantly altered and may 

represent the original composition of the dolomites in this 

area. 

Chemical data (table 5) confirm that the dolomite 

from the core-hole samples contains more iron than pure 

dolomite. The comparison of the X-ray data from the core 

samples with that given by Van Kauwenburgh and others 

( 1990) indicates that the samples from the core are slightly 

deficient in MgO. 

Mineralogy 9 
Table 4. Unit-cell dimensions and unit-cell volumes of 

dolomite from the core hole of this study compared with that 

of dolomite from phosphate mines and with data from the 

literature 

Sample No. a (A) c(A) 

Hardee County core hole (this study) 

F?-87........................................... 4.814 16.057 

F8-87 ........................................... 4.812 16.073 

F1 0-87 ......................................... 4.816 16.087 

F12-87 ........................................ . 

F16-87 ........................................ . 

F18A-87 ..................................... . 

4.817 

4.818 

4.817 

16.082 

16.095 

16.087 

Unit-cell 

volume 

322.25 

322.30 

323.12 

323.16 

323.55 

323.26 

Florida mine samples (Van Kauwenbergh and others, 1990) 

Suwannee River mine................. 4.815 16.033 321.90 

Saddle Creek mine...................... 4.819 16.047 322.72 

Hooker's Prarie mine.................. 4.819 16.026 322.31 

Hardee Complex mine................ 4.814 16.026 321.64 

Florida mine sample (J.B. Cathcart, unpub. data, 1980) 

Lonesome mine........................... 4.817 16.025 322.02 

Data from Howie and Broadhurst (1958) 

Dolomite .................................... .. 

(JCPDS card 11-78). .............. 4.811 16.02 320.97 

Ferroan dolomite ........................ . 

(JCPDS card 34-517)............. 4.819 16.10 323.79 

Ankerite ...................................... . 

(/) 

~ 

0 

a: 

I-

(/) 

(.9 

z 

<( 

z 

z 

0 

(/) 

z 

w 

~ 

0 

--' --' w 

() 

I 

(..) 

(JCPDS card 33-282). ............ 4.824 16.132 325.10 

16.14 

16.12 

16.10 

16.08 

16.06 

16.04 

16.02 

x Ankerite 

F16 0 x Ferroan dolomite 

F10 ooF18 

0F12 

F8 

0 

• sc 

eSR 

HCe e•HP 

~ L 

Dolomite 

EXPLANATION 

F16 0 Corehole sample 

SC • Mine sample 

SC, Saddle Creek 

SR, Suwannee River 

HC, Hardee Complex 

HP, Hooker's Prairie 

L, Lonesome (table 4) 

16.00 +---....---.--------, 

4.80 4.81 4.82 4.83 

A-CELL DIMENSION, 

IN ANGSTROMS 

Figure 3. Relations of a- and c-cell dimensions of dolomite, 

ferroan dolomite, and ankerite compared with these relations 

in the core samples and in samples from phosphate mines, 

Florida. 

Table 5. Chemical analyses of dolomite 

[n.d., not determined; ---, not present; tr., trace; ppm, parts per million] 

CaO ..................... . 

MgO .................. .. 

C02 .................... .. 

FeO ..................... . 

Fe20 3 .................. . 

Si02 ................... .. 

Na20 .................. .. 

K20 .................... .. 

Ti02 ................... .. 

Al20 3 ................. . 

MnO ................... . 

H20 ..................... . 

Total ............. .. 

Dolomite1 

31.27 

21.12 

47.22 

.22 

tr. 

.12 

n.d. 

n.d. 

.02 

99.97 

Ferroan 

dolomite1 

29.23 

12.85 

44.70 

12.06 

.10 

.15 

.06 

.01 

tr. 

.28 

.77 

.02 

100.23 

1 Howie and Broadhurst (1958). 

F18-872 

Ca (3 percent) 

Mg (5 percent) 

Fe (1 percent) 

Na (0.2 percent) 

Ti (0.05 percent 

AI (present) 

Mn (500 ppm) 

2Semiquantitative spectrographic analysis by S.J. Sutley, 

U.S. Geological Survey, of dolomite from the core hole of this 

study. 

Ca/cite.-Calcite crystals (scalenohedrons) that range 

from 0.01 to 0.02 in. in length are present in trace amounts 

in samples F13-87 through F18-87 (from 95- to 124-ft 

depth). The crystals formed between laminae in gray-green 

doloclay beds as shown in the photograph of sample F14-87 

(fig. 4A). Single calcite crystals, hand picked from sample 

F16-87, are shown on fig. 4B. X-ray data indicate that the 

core-hole samples contain trace amounts of calcite, about 5 

percent of the +20-mesh fraction and about 1 percent or less 

of the total rock. 

Clay Minerals 

The clay minerals in the phosphate deposits of Florida 

are a mixture of the common smectite, illite, and kaolinite 

and the less common palygorskite (attapulgite) and 

sepiolite. Smectite is the most abundant clay mineral in the 

phosphorite of the Bone Valley Formation and is present in 

varying amounts in the Peace River Formation. Illite is 

known to be present in minor amounts (Van Kauwenburgh 

and others, 1990), but in the samples studied for this report, 

only the major illite peak at about 10 A could be detected in 

the X-ray diffractograms. Palygorskite and sepiolite are clay 

minerals with crystalline structures consisting of long 

double silicate chains that are parallel to the length of the 

mineral fibers (Carroll, 1970). In general, palygorskite 

occurs in samples from the bottom of the mine pits in the 

land-pebble district, whereas sepiolite is not present or is 

very rare in samples from the mine pits. 

10 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Figure 4. Photographs of calcite crystals from the core hole, 

Hardee County, Fla. A: Calcite crystal embedded in gray-green 

doloclay, along the bedding plane, sample F14-87. 8: Handpicked calcite crystals, sample F16-87. 

Clay-mineral distribution in the minus-150-mesh 

fraction of samples from the core hole is shown on figure 5. 

Illite, although probably present in trace amounts, is not 

shown. Van Kauwenburgh and others (1990) concluded that 

illite probably was detrital in the sediments in the mine pits, 

and we think that the trace amounts of illite in the core 

samples are also detrital. 

Kaolinite.-Kaolinite is the predominant clay mineral 

in the surficial samples of the land-pebble phosphate district 

where it formed as an alteration product of smectite during 

acid weathering (Altschuler and others, 1963), but detrital 

kaolinite has been described from a drill hole in DeSoto 

County (Cathcart, 1989, p. 33). 

Kaolinite is present in the upper three samples 

(F1-87, F2-87, F3-87) from the core hole, where it is 

inversely correlated with smectite (fig. 5), and it is the major 

clay mineral only in the uppermost sample (F1-87). Sample 

F1-87 contains aluminum phosphate minerals (wavellite 

and crandallite) that were derived from apatite during acid 

weathering, and the kaolinite in these samples probably was 

derived from smectite during this acid weathering. 

Palygorskite ( attapulgite ).-Palygorskite is present 

in all of the samples of the Peace River Formation and is 

abundant in those samples that contain carbonate rock 

(dolomitic clay and dolomite). In these samples (fig. 5) it is 

inversely correlated with smectite. Palygorskite is the 

principal clay mineral in the middle part of the Peace River 

Formation (samples F7-87 to F11-87) and in the sample of 

the Arcadia Formation at the base of the core hole (sample 

F18-87). 

Palygorskite is mined from Miocene rocks in northern 

Florida and southern Georgia, is present throughout the 

phosphate deposits of Florida, and is also closely associated 

with phosphate deposits in Africa and the Middle East. 

Sepiolite.-Sepiolite is present in the samples from 

the basal Peace River Formation (F12-87 to F16-87, fig. 5), 

where it is generally more abundant than palygorskite. 

Sepiolite is not present in the sample of dolomite from the 

Arcadia Formation (F18-87). Sepiolite is abundant only in 

the stratigraphically lower parts of the Arcadia Formation 

and may be the only clay mineral in the basal part of the 

Hawthorn Group, in beds of the Tampa Member (Cathcart, 

1989). 

It has been postulated that palygorskite and sepiolite 

in the phosphate deposits and clay deposits of Florida 

formed in a perimarine environment (Weaver, 1984) or in 

ephemeral lakes (Strom and Upchurch, 1985), and in the 

phosphate deposits of the land-pebble district by alteration 

of smectite (Altschuler and others, 1964). Weaver and Beck 

(1977) proposed that palygorskite and sepiolite in the north 

Florida clay deposits were deposited prior to the transgression of the Miocene sea, and, therefore, these minerals 

may be at least partly detrital. 

Because of the wide areal and stratigraphic distribution of these clay minerals in the southern extension of 

the land-pebble phosphate district, it is thought that they are 

of detrital origin, as proposed by Weaver and Beck (1977). 

Smectite.-Smectite is by far the most abundant clay 

mineral in the sediments of Miocene age in Florida. The 

smectites have been described as nontronitic by Altschuler 

and others (1964) and as iron rich by Strom and Upchurch 

( 1985). In a detailed study of the clay mineralogy of the 

land-pebble phosphate deposits, Van Kauwenbergh and 

others (1990) concluded that the smectite-group mineral is 

beidellite, but they pointed out that montmorillonite also 

may be present. Although the X-ray diffraction studies 

made for this report were not detailed enough to precisely 

determine the nature of the smectite, we believe that it is 

likely that the mineral is beidellite, but some montmorillonite is probably present. 

Mineralogy 11 
2 

3 

(f) 4 

a: 5-

w 6 (() 

~ 7 

:::> 

z 8 

w 9 

.....J 10 a.. 

~ 11 

cd:: 

(f) 12 

13 

14-

15-

16 

17 

18-

KAOLINITE 

0 25 50 

/ 

75 0 

SMECTITE 

50 100 0 

PALYGORSKITE 

50 100 

SEPIOLITE 

0 50 

Figure 5. Clay-mineral distribution in samples from the core hole in sec. 7, T. 34 S., R. 24 E., Hardee County, Fla. Amounts 

estimated from X-ray diffractograms, recalculated to 100 percent. 

The origin of the smectite in these deposits is 

questionable. Many writers (Grim, 1933; Mansfield, 1940; 

Gremillion, 1965; Heron and Johnson, 1966; and Weaver 

and Beck, 1977) believed that the smectite was detrital and 

was derived, in part, from alteration of volcanic debris. 

However, several authors (Kerr, 1937, Espenshade and 

Spencer, 1963, McClellan, 1964; and Isphording, 1973) 

could find no evidence of volcanic material in the sediments 

and argued against a volcanic origin. We found no evidence 

of any volcanic debris in the sediments studied for this 

report and do not think that the smectite formed from 

alteration of volcanic material. 

The phosphate particles in the sediments of the 

land-pebble district show evidence of repeated episodes of 

physical reworking and chemical alteration (Altschuler, 

1965). The clay minerals, therefore, must also have been 

reworked in the same way, and, therefore, evidence of their 

original nature has been thoroughly obscured. 

Aluminum phosphate minerals 

Wavellite.-Wavellite, identified in X-ray diffraction 

patterns, is present only in the uppermost sample (F1-87) 

and only in the minus-150-mesh fraction of the sample 

where it occurs as very fine grained, clear needles. The total 

amount of wavellite is about 5 percent of the minus150-mesh fraction and less than 1 percent of the total 

sample. 

Crandallite.-Crandallite is present in trace amounts 

in the minus-150-mesh fraction of sample F1-87 and may 

be present in sample F2-87, from the thin clay bed that 

separates the leached Bone Valley Formation from the 

underlying unleached material. The clay bed is relatively 

impermeable and probably acted as a seal preventing 

leaching of apatite in the underlying beds. The pebble 

fraction of sample F3-87, however, has a small percentage 

of white and cream-colored phosphate particles that are not 

as highly polished as the phosphate particles in lower 

samples. Sample F3-87 may be slightly leached, perhaps 

prior to the deposition of the clay bed of sample F2-87, or 

leached by lateral movement of ground water under the clay 

bed. Beds lower in the section show no evidence of leaching 

and no traces of aluminum phosphate minerals. 

Pyrite 

Trace to minor amounts of pyrite were noted in the 

X-ray diffractograms of the concentrate fraction of samples 

F7-87 through F18-87. The concentrate is that part of the 

-1-mm fraction that sinks in bromoform (specific gravity 

2.86), and pyrite is concentrated in this fraction. The amount 

of pyrite, calculated from the X-ray diffractograms, is 

between 1 and 2 percent. Pyrite was not seen in diffractograms of samples from the Bone Valley Formation or in the 

top samples of the Peace River Formation (samples F1-87 

to F6-87), but iron oxide stains are common in these 

samples, indicating the possibility that pyrite may have been 

present in these samples prior to weathering. 

Pyrite is deleterious in the manufacture of phosphoric 

acid because H2S is formed in the acid treatment. Provided 

that the amount of pyrite present in these samples is 

representative of the amount in the phosphorite of the 

12 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Table 6. Chemical analyses of the minus 1-mm plus 0.1-mm fraction of core samples, Hardee County, Fla. 

[Analyses by U.S. Geological Survey laboratories, Denver, Colo. F by ion-specific electrode by J. Sharkey; Ca and P by induction-coupled plasma 

atomic emission spectrography by D. Fey; Acid insoluble (percent undissolved material) by D. Fey; Mg, Na, Fe, and Ti by optical emission 

spectrography by B.M. Adrian. CaO and P20 5 calculated from Ca and P, and the ratios were calculated by the authors] 

Sample Laboratory Acid Chemical analyses (in percent) Ratios 

No. No. insoluble F Ca CaO 

F3-87 0338-192 57.4 0.82 9.12 12.76 

F4-87 -193 60.7 .82 9.27 12.97 

F5-87 -194 58.8 .66 7.33 10.26 

F6-87 -195 50.0 .94 10.0 13.99 

F7-87 -196 43.2 1.26 15.0 20.99 

F8-87 -197 48.1 .94 11.3 15.81 

F9-87 -198 57.0 .88 9.80 13.71 

F10-87 -199 56.7 .76 8.88 12.42 

F11-87 -200 57.6 .70 8.75 12.24 

F12-87 -201 53.0 .88 10.3 14.41 

F13-87 -202 57.0 .76 9.63 13.47 

F14-87 -203 46.2 .94 11.1 15.53 

F15-87 -204 52.4 .76 7.86 11.0 

F16-87 -205 59.1 .70 7.61 10.65 

F17-87 -206 63.0 .62 6.98 9.77 

F18A-87 -207 51.4 1.06 13.3 18.61 

southern extension, H2S should not be a problem in the 

manufacture of phosphoric acid from the rock. However, 

the amounts of pyrite in the phosphate products should be 

carefully checked in future prospect drilling. 

Micrometeorite (Tektite?) 

A very fine grained metallic sphere was found 

embedded in a phosphate grain (fig. 6) from sample F12-87 

at about 90ft below the surface. X-ray data show that the 

Figure 6. Iron spherule embedded in a phosphate grain in 

sample F12-87 from a core hole, Hardee County, Fla. 

p P20s Mg Na Fe Ti Ca0/P20 5 F/P20 5 

3.80 8.71 0.1 0.2 0.15 0.05 1.465 0.094 

3.83 8.78 .1 .2 .15 .05 1.477 .093 

2.99 6.85 .05 .2 .07 .02 1.498 .096 

4.11 9.42 .1 .2 .1 .02 1.485 .099 

5.80 13.29 1. .7 .7 .02 1.579 .095 

4.47 10.24 .2 .5 .5 .05 1.544 .092 

3.84 8.80 .15 .5 .5 .02 1.558 .100 

3.47 7.95 .2 .3 .3 .03 1.562 .096 

3.22 7.38 1. .5 .5 .05 1.659 .096 

4.05 9.28 .3 .5 .5 .05 1.553 .095 

3.57 8.18 .2 .3 .5 .07 1.647 .093 

3.86 8.84 .2 .3 .5 .05 1.757 .106 

3.02 6.92 .2 .2 .3 .03 1.590 .110 

2.93 6.71 .2 .7 .3 .01 1.587 .104 

2.70 6.19 .15 .3 .2 .02 1.578 .100 

5.10 11.69 .5 .7 .3 .1 1.592 .091 

sphere is composed of elemental iron and therefore may be 

a micrometeorite (tektite?). The spherule fits the definition 

of a tektite by Stokes and Varnes (1955, p. 149), "A glassy, 

rounded body thought to be of meteoric nature. Tektites 

usually appear to weather from sediments of Tertiary age." 

The spherule was deeply imbedded in the phosphate 

grain; about half of the spherule was exposed on the broken 

surface. It seems likely that the sphere was incorporated in 

the phosphate grain as the grain was forming. 

The chemical characteristics of the spherule are 

consistent with a probable meteoric origin. This is the first 

documentation of a micrometeorite (tektite?) in the phosphate deposits of Florida, although tektites were rumored to 

have been found in the material of the open-pit mines. These 

reports could have been about iron balls caused by welding 

spatter in and close to the mining pits. 

CHEMISTRY 

Chemical analyses for phosphorus, calcium, and 

fluorine, the. major elements in apatite, and for acidinsoluble material, the principal diluent, were made of 

the -1-mm +0.1-mm fraction of samples from the drill 

hole. The percentages of CaO and P 20 5 and the ratios 

of Ca0/P20 5 and F/P20 5 were calculated by the authors 

(table 6). 

Semiquantitative spectrographic analyses were made 

of the samples (table 7), and analyses for cadmium, zinc, 

Chemistry 13 
Table 7. Trace-element content of phosphate samples from a core hole in Hardee County, Fla. 

[Values in parts per million.<, less than. Looked for but not detected: As, Au, Bi, Ge, Nb, Sb, Sn, Th, W. 

N, not detected; N5, NlO, at or just below the limit of detection. Analyses by optical emission spectrography by B.M. Adrian, U.S. 

Geological Survey] 

Sample Ag B Ba Be Co Cr Cu Ga La Mn Mo Ni Pb Sr v y Zr No. 

F3 <.5 30 70 <10 50 7 N5 50 20 N5 30 50 500 50 20 500 

F4 <.5 20 150 <10 30 5 <5 70 50 N 5 20 500 50 50 200 

F5 <.5 15 150 N10 15 5 <5 70 30 N 5 20 300 30 30 50 

F6 <.5 15 150 N10 30 7 <5 70 50 N 7 15 500 30 30 50 

F7 <.5 50 100 <10 30 10 <5 70 100 20 10 30 500 30 50 50 

F8 <.5 20 150 <10 20 7 <5 70 150 10 5 20 500 20 50 50 

F9 N 30 150 <1 <10 30 7 <5 70 30 10 5 20 500 20 50 300 

FlO <.5 30 150 <1 N10 30 5 <5 70 30 5 5 20 300 20 30 70 

Fll <.5 15 100 <1 N 20 7 <5 70 50 10 5 20 500 20 30 50 

F12 <.5 20 100 <1 N 20 7 <5 50 50 10 5 20 500 30 50 100 

F13 <.5 20 150 1 N 20 7 <5 70 50 10 5 20 300 20 50 200 

F14 51 30 100 N 20 7 <5 70 50 <5 5 15 500 20 30 50 

F15 <.5 30 100 <1 N 20 5 <5 50 50 N 5 15 500 20 30 100 

F16 <.5 30 150 1 N 20 5 <5 50 50 N 5 20 300 20 30 150 

F17 <.5 15 150 1 N 15 <5 N5 70 50 N 5 10 300 15 30 30 

F18 <.5 20 150 N 30 7 <5 100 70 N 5 20 500 20 100 50 

1 A second analysis of this sample showed 2 ppm; two analyses of a second split of this sample showed 0.5 ppm. 

mercury, and uranium were made of the apatite-concentrate 

fractions of the samples (table 8). Scatter diagrams made 

from the analytical data show a strong positive correlation 

between phosphorus and calcium and fluorine, a moderate 

positive correlation of phosphorus with magnesium, 

sodium, and yttrium, a weak positive correlation of phosphorus with the rare-earth element lanthanum, and a strong 

negative correlation of phosphorus with acid-insoluble 

material (fig. 7). Although calcium and magnesium are 

present in both apatite and dolomite, the strong correlation 

of calcium with phosphorus suggests that most of the 

calcium is in apatite, whereas the moderate correlation of 

magnesium and phosphorus suggests that much of the 

magnesium is in dolomite. The high magnesium contents 

shown on figure 7 and table 6 are caused by the presence of 

discrete dolomite grains in the analyzed samples. Because 

much of the dolomite is soft, the washing and screening 

disaggregated the soft dolomite and therefore, most of the 

dolomite is in the minus-150-mesh fraction. Grains of hard 

dolomite are present in the analyzed fractions of samples 7, 

11, and 18, and therefore, these samples are high in 

magnesium content. 

Ratios of Ca0/P20 5 (table 6) are in the range for 

carbonate fluorapatite (francolite) and tend to increase with 

depth, indicating an increase in substitution in apatite 

toward the base of the drill hole. This increase in substitution in the apatite is also shown by the a-cell dimension 

of the apatite (table 3). 

Trace elements 

The presence of trace elements in phosphorites has 

been recognized for many years. Strutt (1908) first 

determined the presence of uranium in phosphate rock, and 

Mansfield (1927) pointed out that the phosphate deposits of 

the western United States contain possibly significant 

amounts of trace elements. Jacob and others (1933) showed 

that many trace elements are present in phosphate rock of 

the United States. McKelvey and others (1951) presented 

data on the minor metal content of Florida phosphate rock. 

Krauskopf (1955) summarized data on phosphate rock, and 

he concluded (p. 423) that "***most of the elements 

markedly concentrated in phosphate rocks probably owe 

their abundance to organic matter accompanying the 

phosphate rather than to the phosphate itself; only Sr, part of 

the Pb, As, and rare earths and possibly Be and Nb also, 

appear to be dependant on the phosphate." Further, he 

pointed out (p. 423) that "***Sr, Pb, and the rare earths 

substitute for Ca and As for Pin the apatite lattice." At the 

time of Krauskopf's report (1955), there were virtually no 

14 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Table 8. Cadmium, zinc, mercury, and uranium contents of apatite concentrate fractions of 

phosphate samples from a core hole, Hardee County, Fla. 

[Values in parts per million. do., ditto;<, less than, Cd and Zn by optical spectroscopy, D. Fey, analyst; Hg by 

quantitative spectroscopy, P. Hageman, analyst; U by fluorimetric analysis, T. Roemer, analyst. Coefficients of 

correlation: Cd/Zn +0.89, Cd/Hg +0.82, Cd/U +0.20] 

Sample Cd Zn No. 

F1-87 ........................................... 15 116 

F3-87 ........................................... 7 81 

F4-87 ........................................... 5 32 

F5-87 ........................................... 2 50 

F6-87 ........................................... <2 48 

F7-87 ........................................... 2 30 

FS-87 ........................................... 3 43 

F9-87 ........................................... 2 32 

F10-87 ......................................... 3 36 

F11-87 ......................................... 2 32 

F12-87 ......................................... 2 42 

F13-87 ......................................... 2 36 

F14-87 ......................................... 3 33 

F15-87 ......................................... 3 37 

F16-87 ......................................... 3 34 

Fl7-8 ........................................... 3 34 

Fl8-87 ......................................... 5 55 

data on the content of cadmium and mercury in phosphate 

rock. 

Some of the trace elements are known to be necessary 

for plant nutrition; for example-boron, magnesium, and 

molybdenum; others are known to be toxic to plants and 

animals (arsenic, cadmium, mercury, and nickel); and still 

others are necessary for plant nutrition in small amounts but 

are toxic in higher concentrations (cobalt, chromium, 

copper, manganese, and zinc). The trace elements are 

present in phosphate rock in amounts that range from a few 

tenths to several hundred parts per million. 

Variations in trace-element contents (fig. 8) show a 

parallelism with depth. Calcium, magnesium, and fluorine 

show some parallelism; phosphorus has too little variation 

to show much parallelism with the others. Sodium, although 

it is positively correlated with phosphorus, does not show 

the same degree of parallelism, whereas iron and titanium 

are nearly random in their distribution. The trace-element 

contents show a distinct rise in sample 7, just below the 

contact of weathered material with the fresh rock below. 

The contact of weathered and fresh material is placed 

between samples 6 and 7 because iron oxides occur above 

this level, and pyrite is present in the samples below this 

level. 

The analytical data for trace-element contents from 

samples of the core hole are shown in table 7; vertical 

distribution of elements in the core hole is shown on figure 

8, and relations of the elements to one another are shown on 

Hg u Remarks 

0.40 142 Leached Bone Valley Formation. 

.32 150 . ....................... do ......................... 

.34 100 Weathered Peace River 

Formation. 

. 08 107 . ....................... do ......................... 

. 04 90 ........................ do ......................... 

.08 92 Unweathered Peace River 

Formation. 

. 08 98 .. ...................... do ......................... 

. 06 86 ........................ do ......................... 

.08 81 .. ...................... do ......................... 

.06 98 .. ...................... do ......................... 

.12 90 .. ...................... do ......................... 

.12 96 .. ...................... do .......................... 

. 08 110 .. ...................... do ......................... 

. 08 110 .. ...................... do ......................... 

.12 100 .. ...................... do ......................... 

.06 87 .. ...................... do ......................... 

.06 60 Top of Arcadia Formation. 

scatter diagrams (fig. 9). The vertical distribution (fig. 8) 

shows that copper, lead, molybdenum, nickel, and boron are 

higher in sample 7 than in sample 6. Molybdenum, titanium, 

zirconium, barium, and manganese are more or less random 

in distribution; they show little correlation with other 

elements. 

The trace elements may be present in the apatite 

structure, allied with the organic material, or present as 

discrete minerals. For example, the elements that are 

randomly distributed (titanium, zirconium, molybdenum, 

manganese, barium, and boron) probably occur as discrete 

mineral phases-titanium as rutile, zirconium as zircon, 

molybdenum as molybdenite, and so forth. All of these 

minerals are in amounts that are too small to be identified by 

X-ray diffraction. 

Trace elements most likely to be present in the apatite 

structure include vanadium (as V04 substituting for P04), 

the rare earths (lanthanum and yttrium), magnesium, 

sodium, strontium, and perhaps a part of the lead 

substituting for calcium. Other trace elements (chromium, 

copper, nickel, and part of the lead and vanadium) are 

probably allied with the organic material, as indicated by 

Krauskopf (1955). These trace metals roughly parallel one 

another in vertical distribution, and they all show an 

increase below the zone of weathering (fig. 8). The organic 

fraction is depleted in the zone of weathering and is 

abundant in the samples below the zone of weathering. 

Chemistry 15 
t=' 6 

z 

w 

~ 5 

w 

!?::-

6 t=' 

z 

w 

~ 5 

w 

(L 

-

CJ) 4 

:J 

a: 

0 

I 3 (L 

CJ) 

0 

r = +0.96 

•I • 

• 

.... •• 

• • • 

r = +0.41 

• 

• 

I • • • 

I 

I 

• 

• 

• 

• 

• 

• 

~ 2~~--~~--~~--~~--~--

t=' 6 

z 

w 

~ 5 

w 

!?::-

t=' 6 

0.05 0.07 0.1 0.15 0.2 0.3 0.5 0.7 1.0 

MAGNESIUM (PERCENT} 

r = +0.50 • 

• 

• 

I • I I 

• • 

0.2 0.3 0.5 0.7 

SODIUM (PERCENT) 

z r = +0.63 • 

w 

~ 5 

w 

(L 

-

~ 4 

a: 

0 

~ 3 

CJ) 

0 

• • • • c 

• 

• 

& 

• 

I 

(L 2~--~----~--~----~--~ 

10 20 30 50 70 100 

YTTRIUM (PARTS PER MILLION) 

t=' 6 

z 

w 

~ 5 

w 

!?::-

CJ) 4 

:J 

a: 

0 

~ 3 

CJ) 

0 • 

r = +0.97 

• 

1 •• 

•• • • • • •• 

• 

• 

I 

(L 24-~--~~--~~--~~ 

t=' 6 

z 

w 

~ 5 

w 

(L 

-

CJ) 4 

:J 

a: 

0 

~ 3 

CJ) 

0 

I 

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 

FLUORINE (PERCENT) 

• 

r = -0.71 

• 

• 

• 

• • 

• 

••• •• • •• 

(L 2+---------~--------~-, 

40 50 60 

ACID-INSOLUBLE RESIDUE (PERCENT) 

1='6 

z 

w 

~ 5 

w 

!?::-

CJ) 4 

:J 

a: 

0 

~ 3 

CJ) 

0 

r = +0.47 

• I 

• • 

• 

• 

. l 

• • 

• 

I 

(L 2+-~--~~--~~--~~ 

0.05 0.07 0.1 0.15 0.2 0.3 0.5 0.7 

IRON (PERCENT) 

t=' 6 

z 

w 

() 

a: 5 

w 

!?::-

CJ) 4 

:J 

a: 

0 

~ 3 

CJ) 

0 

I 

r = +0.44 • 

• • 

• • 

• 

I 

I 

• • • 

• 

(L 2+---~----~--~ 

30 50 70 100 

LANTHANUM (PARTS PER MILLION) 

Figure 7. Scatter diagrams showing relations of phosphorus to calcium, fluorine, magnesium, sodium, iron, 

yttrium, lanthanum, and acid-insoluble residue. r, coefficient of correlation. 

16 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
a: 

w 

Ill 7 

~ 8 

z 9 

~ 10 

a.. 11 

~ 12 

(j) 13 

14 

15 

16 

17 

18 

Cr Cu Pb Mo Mn 

Pb Mo Mn Ni 

Ni v Zr B 

v Zr B 

Ba 

Ba 

La y 

ITI rrTii 50 70 100 20 30 50 70 100 

La y 

Analyses (parts per million) by optical emission spectrography. N, not detected 

Ca Mg p F Na Fe Ti 

illiiliil .---.-----1 ~ r-r-T1 I I I 1 I I 

5 10 15 .05 .1 .2 .5 1.0 0 5 10 0.5 1.0 1.5 0.2 .3 .5 .7.07 .1 .15 .2 .3 .5 .7 .01 .02 .03 .05 .07 .1 

a: 

w 

Ill 

:2: 

:::1 9 

~ 10 __. 11 a.. 

:2: 12 

;75 13 

14 

15 

16 

17 

18 

Ca Mg 

Weathered 

Fresh 

p F Na Fe Ti 

Ca and P analyses (percent) by induction coupled plasma atomic emission spectrography 

F analyses (percent) by ion specific electrode 

Mg, Na, Ti, and Fe analyses (percent) by optical emission spectrography 

Figure 8. Plots of the distribution of elements in the core samples, Hardee County, Fla. 

Iron is present as iron oxide (hematite?) in the 

weathered samples and as pyrite in the fresh samples. The 

fair positive correlation of iron and phosphorus (fig. 7) 

indicates that a part of the iron content is incorporated as 

either iron oxide or pyrite in the phosphate pellets, in 

addition to being present as discrete mineral particles. 

Trace elements present in the samples in amounts that 

are at or just below the limits of detection include gallium, 

silver, beryllium, and cobalt. Gallium is known to be 

associated with aluminum, and the small amounts of gallium probably are present in the clay minerals of the 

samples. Beryllium is probably present in a beryllium 

mineral, not otherwise identified, and both cobalt and silver 

are probably allied with the organic phase. Silver is present 

in amounts less than 0.5 ppm except in sample Fl4-87, 

where it was 5 ppm. A second split of this sample contained 

2 ppm silver, but analyses of a different split of sample 

Fl4-87 showed only 0.5 ppm silver. The anomalous 

amount of silver in the original split of sample Fl5-87 is 

probably caused by a random distribution of native silver in 

the material, the so-called nugget effect. 

Cadmium 

Cadmium, a toxic element that can be absorbed by 

plants, is present in phosphate particles and in phosphate 

fertilizers in amounts that range from 1 to about 100 ppm 

(Baechle and Wolstein, 1984 ). They thought that the 

cadmium in phosphate rock is allied with the organic 

fraction of the rock. Limits on the maximum amount of 

cadmium that can be present in phosphate rock used to 

make fertilizer have been set at 20 ppm. 

Semiquantitative spectrographic analyses of several 

hundred samples of phosphate pebble and concentrate from 

the land-pebble phosphate district of Florida report 

cadmium in most samples as being at or below the limit of 

detection (20 ppm), whereas the highest amounts of 

cadmium in these samples were 30-50 ppm (U.S. Geological Survey, unpub. data, 1960-80). Data published by 

Baechle and Wolstein (1984) show that Florida phosphate 

rock contains from 3 to 12 ppm cadmium, and they pointed 

out that the average cadmium content of Florida phosphate 

rock, reported from the literature, is 8 ppm. All of these data 

Chemistry 17 
50 • 50 • 50 

30 • • • 30 • • • 30 • • • Cr 2 3 4 4 

20 • 2 • 5 20 20 • • 2 5 

15 • • 15 15 • • • 

3 5 7 10 7 10 15 20 30 10 15 20 30 

Cu Ni Pb 

50 50 

30 30 

Cr 

20 20 

15 15 

1.5 3 5 7 10 15 20 ~ LO C\.1 C") LO t-- 0 0 ~ 0 0 0 0 

Mo c) q c) c) c) c) 0 0 

50 50 Ti • 

30 30 • • • 

Cr 2 2 

20 20 • • • 2 3 

15 15 

I I 

50 70 100 150 200 300 500 0.04 0.10 0.20 0.30 0.34 

Zr Hg 

10 10 • 10 

7 7 2• • • 7 

Cu 6 

5 5 • • 4 5 

3 3 3 

5 7 10 15 20 30 10 15 20 30 50 ~ LO C\.1 C") LO t-- 0 0 ~ 0 0 0 0 

Ni Pb c) q c) c) c) c) c) 0 

Ti 

0.1 0.1 • 

0.07 0.07 • 

0.05 • 0.05 • •2 • • • 

Ti 0.03 0.03- •2 

0.02 • 0.02-• •• 2 2 

0.015 0.015 

0.01 0.01 

I I 

30 50 70 100 150 200 300 500 0.04 0.10 0.20 0.30 0.34 

Zr Hg 

Figure 9. Scatter diagrams showing relations of trace metals in samples from the core hole in Hardee County, Fla. 

Values are in parts per million, except Ti, in percent. Numbers beside dots show number of plots at that location. Plots 

without numbers are single samples. 

18 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
are for phosphate rock from the land-pebble district, and 

there are no data in the literature for the cadmium content of 

the phosphate rock from the southern extension of the 

land-pebble district. 

Data from samples taken from the core hole show that 

two samples of the Bone Valley Formation (F1-87 and 

F3-87) contain 15 and 7 ppm cadmium, whereas amounts in 

the phosphate concentrate from the Peace River Formation 

range from less than 2 to 5 ppm (table 8). The concentrate 

samples from the Bone Valley are cream, white, and gray, 

and probably are low in organic content, whereas the 

samples from the Peace River Formation are black, jet 

black, brown, and gray, and may be high in organic 

material. However, the contents of zinc are very high in the 

top samples of the Bone Valley Formation ( 115 and 81 ppm, 

respectively), whereas the zinc contents of the concentrate 

samples from the Peace River Formation range from 30 to 

55 ppm. In these samples, the cadmium likely is present in 

the zinc sulfide mineral sphalerite rather than concentrated 

in the organic fraction. The coefficient of correlation for 

zinc and cadmium is +0.89, a very good positive 

correlation, as indicated in the scatter diagram (fig. 10). It 

should be pointed out, however, that the strong positive 

correlation is dependant on three samples-F1-87, F3-87, 

and F18-87 (fig. 10). 

Most of the economic phosphate in the southern 

extension is in the Peace River Formation, and if the data 

presented herein on the cadmium content of the phosphate 

rock are representative, it is likely that the cadmium content 

of the phosphate concentrate from the southern extension 

120 

z 

0 

_J 100 

_J 

~ 

a: 

w 80 

a_ 

(f) 

1--

a: 

<( 

a_ 

z 

() 

z 

N 

60 

40 

• 1 r = +0.89 

• 3 

• 18 

5 EXPLANATION 

6 • • •18 12 ~ 15 • Plot of Cd/Zn relation /10 13. 1~6,17 of numbered sample 9,11-: \ •4 

7 14 

0 5 10 15 

CADMIUM, IN PARTS PER MILLION 

Figure 10. Scatter diagram showing relations of cadmium 

and zinc, in the concentrate fraction of the core samples, 

Hardee County, Fla. Sample data are in table 8. 

will be found to be below 20 ppm, and there should be no 

danger of cadmium poisoning of vegetable crops grown on 

land fertilized by this type of Florida phosphate. Baechle 

and Wolstein (1984) indicated that there is no buildup of 

cadmium in soils fertilized by phosphate rock with the 

content of 7-12 ppm cadmium. 

It is evident, therefore, that the amount of cadmium in 

the phosphate rock from the southern extension of the 

Florida phosphate district is not a cause for concern. It will 

be necessary, however, to continue to determine the 

cadmium content of the phosphate deposits of the southern 

extension, at least until the average content can be verified. 

Mercury 

Mercury is present in phosphate rocks of the United 

States and elsewhere in the world in trace amounts. Gunnarsson (1983) stated that mercury contents of marine 

phosphate rock range from 0.03 to 0.33 ppm and in igneous 

apatite deposits from 0.01 to 0.15 ppm. 

Mercury in surficial sand in peninsular Florida ranges 

from 0.015 to 0.05 ppm, but surface muck and swamp 

deposits contain as much as 0. 70 ppm (Shacklette and 

others, 1971 ). 

Unpublished data from the U.S. Geological Survey 

(J.B. Cathcart, unpub. data, 1991) indicate that surficial 

sand of Pleistocene and Holocene age in the land-pebble 

phosphate district contains an average of 0.02 ppm mercury. 

Samples of the pebble fraction (+20 mesh) from the 

land-pebble district contain from 0.02 to 0.58 ppm and 

average 0.075 ppm. The concentrate fraction contains from 

0.03 to 0.63 ppm mercury and averages 0.17 ppm. Leached 

phosphate products contain somewhat higher amounts of 

mercury, from 0.04 to 0.75 ppm, and the average of 65 

samples is 0.28 ppm. 

Among the samples of phosphate concentrate 

analyzed for this report (table 8), the samples of leached 

Bone Valley contained 0.32 and 0.40 ppm mercury, 

whereas the samples from the Peace River Formation 

contain from 0.04 to 0.12 ppm mercury. 

The mercury content of the samples from this core is 

consistent with the data from the land-pebble district and 

closely matches the data in Gunnarsson (1983). These data 

indicate that the amount of mercury in phosphate rock is too 

low to be of concern and confirms the statement of 

Gunnarsson (1983, p. 29) that "The very low content of Hg 

cannot possibly cause any problems." 

ECONOMIC GEOLOGY 

The factors that determine the economics of mining 

phosphate rock in Florida include, in no special order: 

(a) Total thickness to be mined. (b) Ratio of cubic yards that 

must be moved per ton of product. (c) P20 5 content of the 

Economic Geology 19 
w ~I-

::J<( zi _a.. 

~CI) 

::::)0 

_JI APATITE 

<(D... DOLOMITE QUARTZ WEIGHT PERCENT 

0 25 0 25 50 0 50 100 0 25 50 75 100 0 25 50 75 100 

L___j 

1 

2 

3 

4 

5 

a: 

w 6 

(]) 7 ~ 8 

::J 

z 9 

w 10 _J 

0.... 11 

~ 12 <( 

Cl) 13 

14 

15 

16 

17 

18 

Figure 11. Distribution of minerals (except clay) in and weight percent of -150 mesh fraction of the core samples, Hardee 

County, Fla. Values are in percent. Data from X-ray diffractograms, recalculated to 100 percent. 

recoverable products. (d) Content of major compounds that 

are deleterious in making fertilizer products from the 

rock-Al20 3, Fe20 3, MgO, CaO, and fluorine. (e) Content 

of potentially damaging trace elements, cadmium, mercury, 

selenium, and arsenic, for example. (f) Content of trace 

elements necessary for plant nutrition, manganese, boron, 

and molybdenum, for example. (g) Content of potentially 

recoverable byproduct elements, uranium, vanadium, and 

fluorine. (h) The amount of the -150 mesh (slime) fraction. 

Economic feasibility cannot be adequately determined from a single drill hole, but data from this drill hole 

will indicate whether the deposit might be economic or 

noneconomic. 

Total thickness of material that must be mined in this 

drill-hole area is about 120 ft, considerably greater than 

thicknesses in the land-pebble district. It is likely that 

thicknesses greater than about 100 ft will require a mining 

technique that involves removing a part of the overburden, 

forming a bench on which the dragline would then mine the 

remaining overburden and ore. This technique has been 

used successfully in North Carolina and to a lesser extent in 

the land-pebble district and should cause no technical 

problems. 

The ratio of cubic yards moved per ton of product will 

be greater in the southern extension than in the land-pebble 

district. 

The recoverable phosphate products in the landpebble phosphate district include the plus 1 mm (pebble) 

and the minus 1 mm plus 0.1 mm (concentrate) separated by 

froth flotation from quartz sand. 

The P 20 5 content of the recoverable product in the 

southern extension will be lower than in the land-pebble 

district. The apatite of the southern extension is more highly 

substituted, and the P20 5 content of the phosphate products 

ranges from less than 30 to about 32 percent and averages 

about 31 percent (Cathcart, 1989). 

The content of major compounds that are deleterious 

in processing are not above the economic levels, except for 

MgO. 

The content of the potentially damaging trace 

elements are within limits of phosphate products currently 

being mined in Florida and North Carolina, as are the trace 

elements needed for plant nutrition (tables 6-8). 

Potentially recoverable byproducts, except for 

fluorine, are in lower amounts than in the land-pebble 

district. 

The amount of the minus-150-mesh fraction in the 

samples from the core hole ranges from 17 to 90 percent and 

averages about 25 percent (fig. 11). The minus-150-mesh 

fraction is composed of clay minerals (fig. 5), quartz, 

apatite, and large amounts of dolomite that range from 3 to 

90 percent, and average about 60 percent (fig. 11). The 

settling characteristics of this fraction will be different from 

20 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Figure 12. Phosphate grains ( + 1-mm fraction) from the Bone 

Valley Formation, core-hole sample F1-87, Hardee County, 

Fla. A: A, dull-white grains; B, shiny tan pellet; C, shiny white 

pellet. 8: A, amber phosphatized shell fragment; B, tan shiny 

pellet; C, shark tooth; D, fish tooth; E, phosphatized rock 

fragment. 

the settling characteristics in the land-pebble district. The 

large amount of dolomite may cause the fraction to settle 

quickly, but this must be determined for each mining site. 

Pyrite is present in trace amounts in samples F7-87 

to Fl3-87 and in larger amounts in samples F14-87 to 

F18-87. The average amount of pyrite is only about 

1 percent and should not be a problem in processing. 

In general, then, the economic parameters all are less 

favorable for the southern extension than for the landpebble district, but it is likely that the phosphate deposits in 

the southern extension can be mined, although at a higher 

cost. 

Environmental restrictions have not been considered 

but could be a problem when the mining companies apply 

for permits to mine and process the deposit. 

PHOSPHATE PARTICLES 

Bone Valley Formation 

Coarse phosphate particles (> 1 mm) in the samples of 

the Bone Valley Formation (F1-87, F2-87, F3-87) are 

shiny, tan to light-brown, and white; there are some black as 

well as dull white and partly leached grains (fig. 12A). The 

dull-white grains are altered by weathering and contain 

aluminum phosphate minerals (wavellite and crandallite) as 

well as apatite. The phosphate grains may be structureless, 

phosphatized rock fragments, phosphatized shell fragments, 

and a few fish and shark teeth (fig. 12B). Some of the grains 

are broken and rerounded, and some are internal molds of 

fossils. 

Fine phosphate particles (<1 mm, >0.1 mm; concentrate) in samples of the Bone · Valley are white, gray, 

brown, tan, cream, and some (<5 percent) black. Most of the 

pellets are well rounded and structureless; broken fragments 

are common, and some phosphatized shell fragments and 

dull-white or gray pellets contain crandallite as well as 

apatite (fig. 13). 

Peace River Formation-Upper Part 

The coarse phosphate fraction from the upper part of 

the Peace River Formation (samples 4--87 to 1 0-87) 

Figure 13. Phosphate concentrate fraction, sample F3-87, 

Bone Valley Formation from a core hole, Hardee County, Fla. 

Black grains (A) are highly polished black and brown rounded 

phosphate pellets, some broken and rerounded. Gray subangular, translucent grains (B) are phosphatized fossil fragments. 

Clear grains (C) are quartz. 

Phosphate Particles 21 
Figure 14. Phosphate grains from samples from a core hole 

in Hardee County, Fla. A: Sample F6-87. A, brown, shiny, 

rounded S!ructureless pellet. B, shark tooth. C, shiny white 

phosphatized internal mold of gastropod, contains some 

quartz silt. 8: Sample F7-87. A, rounded quartz grains and 

black and gray phosphate grains cemented by phosphate. B, 

shiny black rounded grains. Top grain is broken and 

rerounded. White areas are fine-grained dolomite plastered on 

grain surfaces. 

consists of grains varying in color, luster, and shape. Some 

are shiny brown, tan, or gray; some are cream or white; and 

a few are black. The grains include structureless, rounded, 

almost spherical pebbles; phosphatized fossil teeth; phosphatized rock fragments that consist of fine sand-size quartz 

and phosphate cemented by apatite; and phosphatized 

internal molds of fossils (fig. 14). Some of the grains are 

broken and rerounded, and have cracks filled with 

secondary apatite (fig. 15). 

The concentrate fraction of the upper part of the 

Peace River Formation contains pellets that are mostly 

brown, tan, or gray; some are cream and white, and a few 

are black. Pellets are structureless and nearly spherical or 

are rod shaped. Some phosphatized dolomite grains and 

amber, translucent (gray in the photograph), subangular 

phosphatized shell fragments are present (fig. 16). 

Peace River Formation-Lower Part 

The coarse fraction of the lower part of the Peace 

River Formation (samples F11-87 to F18-87) consists 

predominantly of black and brown phosphate pebbles, many 

of which are almost spherical (fig. 17A), some are gray and 

tan, and there is a trace of white grains. Phosphatized rock 

fragments (fig. 17 B) are common in all samples; some are 

partly phosphatized sandy dolomite grains. 

The concentrate fraction of the lower part of the 

Peace River Formation contains predominantly black (some 

jet black) and lesser amounts of dark-gray, brown, tan, 

gray-green, and white polished phosphate. particles, some 

phosphatized rock fragments that are dull rather than 

polished, and some phosphatized fossil fragments (fig. 18), 

including fish and shark teeth and fossil molds. 

The ratio of coarse to fine-grained phosphate in the 

Bone Valley samples is considerably different from the ratio 

in the Peace River samples. The coarse (pebble) fraction is 

much more abundant than ·the fine (concentrate) fraction 

in the Bone Valley Formation, where the ratio of pebble 

to concentrate ranges from 3.1 to 8.1 to 1 and averages 5.6 

to 1. 

In contrast, the samples from the Peace River 

Formation contain much more fine-grained than coarsegrained phosphate. Ratios of pebble to concentrate range 

Figure 15. Gray-brown phosphate grain from sample F14-87 

from a core hole in Hardee County, Fla. A, cracks filled with 

secondary apatite; B, broken and rerounded grain edges. 

22 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Figure 16. Phosphate grains (-1 mm +0.1 mm) from samples 

from a core hole in Hardee County, Fla. A: From sample 

F8-87, near the top of the Peace River Formation. Black, shiny 

phosphate grains are rounded; one is broken and the edges are 

rerounded. Clear grains are quartz. 8: From sample F1 0-87. 

Phosphate grains are black and rounded. Quartz grains are 

clear. S, phosphatized shell fragment. 

from 0.07 to 0.91 to 1 and average 0.46 to 1. However, the 

lowermost samples, F17-87 and F18-87, contain about 

equal amounts of the pebble and concentrate fractions; 

ratios average 0.98 to 1. The ratios do not seem to have any 

periodicity. Only the sharp difference between the ratios of 

the Bone Valley and Peace River Formations appears to be 

significant (fig. 19). 

REFERENCES CITED 

Altschuler, Z.S., 1965, Precipitation and recycling of phosphate in 

the Florida land-pebble phosphate deposits: U.S. Geological 

Survey Professional Paper 525-B, p. B91-B95. 

Figure 17. Phosphate grains (+ 1 mm) from samples from a 

core hole in Hardee County, Fla. A: From sample F14-87. 

Black, spherical phosphate pellet. 8: From sample F16-87. 

A, black, shiny phosphate grains. B, gray phosphatized rock 

fragments. 

Altschuler, Z.S., Cathcart, J.B., and Young, E.J., 1964, Geology 

and geochemistry of the Bone Valley Formation and 

its phosphate deposits, west-central Florida: Geological 

Society of America, Annual Meeting, Miami Beach, Fla., 

1964, guidebook for field trip 6, 68 p. 

Altschuler, Z.S., Dwomik, E.J., and Kramer, H., 1963, Transformation of montmorillonite to kaolinite during weathering: Science, v. 141, p. 148-152. 

Baechle, H.T., and Wolstein, F., 1984, Cadmium compounds in 

mineral fertilizers: London, The Fertilizer Society Proceedings, no. 226, 18 p. 

Bernardi, J.P., and Hall, R.B., 1980, Comparative analysis of the 

central Florida phosphate district to its southern extension: 

Mining Engineering, p. 1256--1261. 

References Cited 23 
Figure 18. Phosphate feed fractions (-1 mm +0.1 mm) from 

samples from a core hole in Hardee County, Fla. A: Black 

grains are shiny black and brown phosphate pellets. Gray 

grains are tan and gray phosphate pellets. Clear grains are 

quartz. From sample F14-87. 8: Black grains are rounded 

phosphate pellets, one broken and rerounded. The irregular 

black grain in the upper right corner of the photograph is a 

fossil fragment. Clear grains are quartz; a rutilated quartz grain 

is in the center of the photograph. The finer quartz grains are 

angular. From sample F18-87. 

Carroll, D., 1970, Clay minerals-a guide to their X-ray 

identification: Geological Society of America Special Paper 

126, 80 p. 

Cathcart, J.B., 1963, Economic geology of the Keysville quadrangle, Florida: U.S. Geological Survey Bulletin 1128,82 p. 

___ 1985, Economic geology of the land-pebble phosphate 

district of Florida and its southern extension, in Cathcart, 

J.B., and Scott, T.M., eds., Florida land-pebble phosphate 

district: Geological Society of America, Annual Meeting, 

Orlando, Fla., 1985, field-trip guidebook, p. 4-27. 

___ 1989, Economic geology of the land pebble phosphate 

district and its southern extension, in Scott, T., and 

10 

E' 8 E 

T""" 

E' c:i 

E + 

T""" 6 I I 

w 

w I-

.....J <( 

co a: 

co I- 4 w z a_ w 

0 

z 

0 2 0 

0 

2 4 6 8 10 12 14 16 18 

Bone I SAMPLE NUMBER 

Valley . I Format1on 1 

Peace River Formation 

jArcadia 

I Formation 

Figure 19. Ratios of coarse to fine phosphate grains in samples 

F1-87 through F18-87 from a core hole, Hardee County, Fla. 

Pebble and concentrate were not separated for sample 2. 

Cathcart, J., eds., Florida phosphate deposits: International 

Geologic Congress, 28th, Washington, D.C., field-trip 

guidebook, T 178, p. 18-38. 

Cooke, C.W., 1945, The geology of Florida: Florida Geological 

Survey Bulletin 29, 339 p. 

Dall, W.H., 1892, Neogene of North America: U.S. Geological 

Survey Bulletin 84, 349 p. 

Eldridge, G.H., 1893, A preliminary sketch of the phosphates of 

Florida: American Institute of Mining Engineers Transactions, v. 21, p. 196-231. 

Espenshade, G.H., and Spencer, C.W., 1963, Geology of the 

phosphate deposits of northern peninsular Florida: U.S. 

Geological Survey Bulletin 1118, 115 p. 

Gremillion, L., 1965, The origin of attapulgite in the Miocene 

strata of Florida and Georgia: Tallahassee, Florida State 

University Ph.D. dissertation, 159 p. 

Grim, R.E., 1933, Petrography of the fuller's earth deposits, 

Olmstead, Illinois, with a brief study of some non-Illinois 

earths: Economic Geology, v. 28, no. 4, p. 344-363. 

Gunnarsson, 0., 1983, Heavy metals in fertilizers-Do they cause 

environmental and health problems?: Fertilizers and Agriculture, no. 85, p. 27-41. 

Heron, S.P., and Johnson, H.S., 1966, Clay mineralogy, stratigraphy, and structural setting of the Hawthorn Formation, 

Coosawhatchie district, South Carolina: Southeast Geology, 

v. 7, p. 51-63. 

Howie, R.A., and Broadhurst, F.M., 1958, X-ray data for dolomite 

and ankerite: American Mineralogist, v. 43, p. 1210--1214. 

Isphording, W.C., 1973, Discussion of the occurrence and origin of 

sedimentary palygorskite/sepiolite deposits: Clay and Clay 

Minerals, v. 21, p. 391-401. 

Jacob, K.D., Hill, W.L., Marshall, H.L., and Reynolds, D.S., 1933, 

Composition and distribution of phosphate rock with special 

reference to the United States: U.S. Department of Agriculture Technical Bulletin 364, 89 p. 

24 Mineralogy, Chemistry of Samples, Land-Pebble Phosphate District, Florida 
Kerr, P.F., 1937, Attapulgus clay: American Mineralogist, v. 22, 

p. 548. 

Krauskopf, K.B., 1955, Sedimentary deposits of rare metals, in 

Bateman, A.M., ed., Economic Geology Fiftieth Anniversary Volume 1905-1955: Lancaster, Pa., Economic 

Geology Publishing Co., p. 411-463. 

Lehr, J.R., McClellan, G.H., Smith, J.P., and Frazier, A.W., 1968, 

Characterization of apatites in commercial phosphate rocks, 

in Colloque International sur les phosphates mineraux 

soli des, Toulouse, 1967, v. 2, Phosphates naturalsphosphates dans l'agriculture: Paris, Societe Chimique de 

France, p. 29-44. 

Mansfield, G.R., 1927, Geography, geology, and mineral resources 

of part of southeastern Idaho: U.S. Geological Survey 

Professional Paper 152, 453 p. 

___ 1940, Introduction, to Clay investigations in the southern 

states, 1934-35: U.S. Geological Survey Bulletin 901, 

p. 1-22. 

___ 1942, Phosphate resources of Florida: U.S. Geological 

Survey Bulletin 934, 82 p. 

Matson, G.C., 1915, The phosphate deposits of Florida: U.S. 

Geological Survey Bulletin 604, 101 p. 

Matson, G.C., and Clapp, F.G., 1909, A preliminary report on the 

geology of Florida: Florida Geological Survey, 2d annual 

report, p. 28-173. 

McClellan, G.H., 1964, Petrology of attapulgus clay in North 

Florida and southwest Georgia: Urbana, University of 

Illinois Ph.D. dissertation, 127 p. 

___ 1980, Mineralogy of carbonate fluorapatite, in Phosphatic 

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Journal, v. 137, pt. 6, p. 675-681. 

McClellan, G.H., and Lehr, J.R., 1969, Crystal chemical investigation of natural apatites: American Mineralogist, v. 54, 

p. 1374-1391. 

McKelvey, V.E., Cathcart, J.B., and Worthing H.W., 1951, 

Preliminary note on the minor-metal content of Florida 

phosphate rock: U.S. Geological Survey Report TEM-236, 

6 p. 

Olson, N.K., 1966, ed., Geology of the Miocene and Pliocene 

Series in the North Florida-South Georgia area: Atlantic 

Coastal Plain Geological Association, 7th Annual Field 

Trip, guidebook, 94 p. 

*U.S. GOVERNMENT PRINTING OFFICE: 1991-673-049/46012 

Scott, T.M., 1988, The lithostratigraphy of the Hawthorn Group 

(Miocene) of Florida: Florida Geological Survey Bulletin 

59, 148 p. 

Shacklette, H.T., Boerngen, J.G., and Turner, R.L., 1971, Mercury 

in the environment-Surficial materials of the conterminous 

United States: U.S. Geological Survey Circular 644, 5 p. 

Stokes, W.L., and Varnes, D.J., 1955, Glossary of selected 

geologic terms: Colorado Scientific Society Proceedings, 

v. 16, 165 p. 

Strom, R.N., and Upchurch, S.B., 1985, Palygorskite distribution 

and silicification in the phosphatic sediments of central 

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International Geologic Correlation Program 156, p. 118-

126. 

Strutt, R.J., 1908, Helium and radioactivity in r~e and common 

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v. 80, p. 572-594. 

Van Kauwenbergh, S.J., Cathcart, J.B., and McClellan, G.H., 

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of Florida: U.S. Geological Survey Bulletin 1914, 46 p. 

Van Kauwenbergh, S.J., and McClellan, G.H., 1985, Variations in 

the mineralogy of the Florida phosphate districts, in Cathcart, J.B., and Scott, R.M., eds., Florida land-pebble 

phosphate district: Geological Society of America Annual 

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Vernon, R.O, 1951, Geology of Citrus and Levy Counties, Florida: 

Florida Geological Survey Bulletin 33, 256 p. 

Weaver, C.E., 1984, Origin and geologic implications of the 

palygorskite of the southeast U.S., in Palygorskite/sepiolite, 

occurrences, genesis, and uses: Elsevier Publishing Co., 

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Weaver, C.E., and Beck, K.C., 1977, Miocene of the southeast 

United States-A model for chemical sedimentation in a 

perimarine environment: New York, Elsevier Publishing 

Co., 234 p. 

Webb, S.D., and Crissinger, D.B., 1983, Stratigraphy and 

vertebrate paleontology of the central and southern 

phosphate districts of Florida, in Central Florida phosphate 

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Section, March 1983, field-trip guidebook, p. 28-72. 

References Cited 25 



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