Differential Thermal 

Analysis of Selected 

Borate Minerals

GEOLOGICAL SURVEY BULLETIN 1036-K

Differential Thermal 

Analysis of Selected 

Borate Minerals

By ROBERT D. ALLEN

A CONTRIBUTION TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1036-K

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by tlie Superintendent of ttocuments, U. IS^ <^vernrne1nt Printing Office 

Wasljlngton 25, Dt Ci * Price IS cent* (paper cover) :
CONTENTS

Page

Abstract__...._____________._.._.______________ 193

Introduction. ___ __________________________________________ 193

Acknowledgments. _________________________________________ __ 194

Apparatus and equipment._____________________________ ____ 194

Experimental procedure.___________.:______________________________ 194

Results_______________________________________ 196

Discussion__________________ ________________________ _ 204

Application to semiquantitative analysis of eolemanite-ulexite mixtures. __ 204

References cited.._____________________________________________ 208

ILLUSTKATIONS

FIGURE 19. Differential thermal analysis curves of bakerite and of synthetic

borax. ____________________.__________ 197

20. Differential thermal analysis curves of colemanite and of

ginorite____________________________________________ 198

21. Differential thermal analysis curves of howlite and of kernite_ _ 199

22. Differential thermal analysis curves of meyerhofferite and of

priceite____________________________________________ 200

23. Differential thermal analysis curves of probertite and of synthetic sassolite_____________________________________ 201

24. Differential thermal analysis curves of searlesite and of

tincalconite_ ___________________________________ 202

25. Differential thermal analysis curves of ulexite and of barium

chloride dihydrate____________________________ _ 203

26. Differential thermal analysis curves of mixtures of eolemanite

and ulexite___________________________ 205

27. Working curve for the semiquantitative determination of

colemanite and ulexite___________________________ 206

28. Differential thermal analysis curves of 13 borates______ -_ 207

nx

A CONTRIBUTION TO GEOCHEMISTRY

DIFFERENTIAL THERMAL ANALYSIS OF SELECTED 

BORATE MINERALS

By EGBERT D.

ABSTRACT

Differential thermal analysis curves of bakerite, borax, oolemanite, ginorite, 

howlite, kernite, meyerhofferite, priceite, probertite, sassolite, searlesite, tincalconite, and ulexite were prepared with a portable differential thermal analysis 

apparatus. These minerals yield distinctive endothermic curves between 50° C 

and 650° C. Thermal curves of synthetic mixtures of colemanite and ulexite 

demonstrate the, practicality of semiquantitative analysis of borate mineral mixtures with the portable apparatus.

INTRODUCTION

In 1953 the writer began a differential thermal analysis study of 

selected borate minerals. The possibility of using differential thermal 

analysis methods on borates was discussed with George T, Faust of 

the Geological Survey who pointed out that the low fusion temperatures of the borate minerals and their well known glass-forming tendencies would set an upper temperature limit to the practical range of 

investigations. Preliminary investigations confirmed these views and 

showed the inadvisability of heating borate minerals to temperatures 

approaching 1000° C. The resulting fusion product may bind the 

thermocouple and crucible with such tenacity that the two can be separated only by breaking the thermocouple. Furthermore, the fused 

borate is removed from the crucible only with great difficulty.

Three modifications in the usual differential thermal analysis procedure obviate the difficulty pointed out above: (1) the run is discontinued at a temperature of 650° C or less; (2) several of these 

minerals are mixed with equal weights of aluminum oxide to lessen 

the adhesive effect; (3) the crucible is removed from its pedestal immediately after completing a run.

Differential thermal analysis used in conjunction with microscopic 

examination is found to be a satisfactory method for the identification 

of the 13 borate minerals investigated. Although these minerals can 

usually be identified with the petrographi.c microscope, positive identification is not always possible, especially for flne-crystallina varieties, 

The following minerals and pairs of minerals are occasionally troublesome: bakerite, borax, colemanite-howlite, ginorite, howlite-priceite, 

meyerhofferite, probertite, sassolite, searlesite, tincalconite, and ulexite.

A portable differential thermal analysis unit such as the one used 

in this investigation can be operated after a few hours of practice; 

such a unit is relatively inexpensive, costing about $500 at current 

market prices.

.41T880 57 .'.'-. , 193
194 CONTRIBUTIONS TO GEOCHEMISTRY

ACKNOWLEDGMENTS

Acknowledgments are due the following colleagues in the Geological 

Survey: The study was suggested by Ward C. Smith. The first experimental work was done with the assistance of Paul D. Blackmon. 

The methods of differential thermal analysis and the application to 

the borate minerals were discussed with George T. Faust. Their application to semiquantitative analysis of borate mineral mixtures was 

suggested by Earl Ingerson.

APPARATUS AND EQUIPMENT

Hendricks, Goldich, and Nelson (1946) described a portable differential thermal analysis unit which they used in the study of bauxitic 

clays. An improved model of this apparatus has been in Use on various 

problems in the past eight years. Parker, Hathaway, and Blackmon 

(1956) have prepared a set of reference curves, chiefly clays, with the 

modified Eberbach unit. This apparatus has been found very well 

adapted to the differential thermal analysis study of borates.

A variable transformer calibrated to read voltage drop was used 

in place of the variable resistance supplied with the above unit.

EXPERIMENTAL, PROCEDURE

Starting with a cold furnace, a heating rate of 30° C per minute 

was found to give greater amplitude and more measured area under 

the curve than the more conventional slower heating rates of 10° C 

or 15° C per minute. The relation between heating rate and measured 

area under the curve has been described by Wittels (1951). The 

heating rate of 30° C per minute was obtained with the following 

voltage drop settings on the transformer:

Degrees Voltage

centigrade drop

0-200 82

200-300 85

300-400 90

400-500 100

Between 500° C and 650° C, a temperature range utilized in the 

examination of bakerite and howlite, the 100-volt setting gave a 

heating rate of 25° C per minute. The endothermic troughs for these 

two minerals would probably occur at slightly higher temperatures 

if the 30° C per minute heating rate were used in the 500° C to 650° C 

range. Temperature readings were made at 10° C intervals, the 

smallest interval on the thermometric scale of this unit. Galvanometer deflections were read to the nearest quarter-of-a-scale division.

Crucibles no. 1, 2, and 3 were used interchangeably without calibration of their respective thermocouples; errors introduced by this procedure are below the resolution range of the instrument. Samples 

were sieved to 50+200 mesh, a size range that is satisfactory for 

this work, and tamped lightly into the crucibles. Faust (1950, p. 215)
THERMAL ANALYSIS OF BORATE MINERALS 195

has pointed out that very fine sizes tend to broaden the base of an 

endothermie trough. Extremely tight packing was avoided because 

the amplitude and inflection temperatures for a given trough appeared 

to increase and because tightly packed samples were often difficult 

to remove after the runs were completed. 

The following minerals were considered:

Bakerite________ ___ _ ___ Ca8B10Si8O35-6H2O

Borax__________________ Na_B4O7-10H2O

Colemanite_ ______________________ Ca2B8Ou-5H2O

Ginorite______________________ Ca2BuO23-8H2O

Howlite_._________________ Ca2SiB8O9 (OH) 5

Kernite__-________________ Na2B4O7-4H2O

Meyerhofferite.______________ Ca2B8Ou.7H2O

Priceite...________________ Ca4BioOi9-7H2O 

Probertite.________________ NaCaB5O9-5H2O 

Sassolite-_________________ B2O3 -3H2O

Searlesite__________________ NaB(SiO3) 2 -H2O

Tincalconite.._____________ Na2B4O7-5H2O 

Ulexite.--________________ NaCaB5O9-8H2O

The minerals, many of which are from type localities (indicated adjacent to the differential thermal analysis curves), were examined 

microscopically to ascertain identity and purity. Specimens of 

bakerite. ginorite, and priceite were also analyzed chemically and 

identified by X-ray examination (Kramer and Alien, 1956; Alien and 

Kramer, 1957).

Colemanite, howlite, priceite, probertite, and searlesite were mixed 

with equal weights of reagent-grade aluminum oxide because preliminary runs had indicated that these minerals are difficult to remove 

from the crucibles after heating to the requisite temperatures; it was 

necessary to mix sassolite with A12O3 in the ratio of 1:3. Even with 

this precaution it is advisable to remove a crucible from its pedestal 

immediately after finishing a run. This should be done for all borates.

Experimental evidence indicates that reaction between aluminum 

oxide and these borates is negligible or absent up to the requisite 

temperature for each mineral. Unheated and heated mixtures of 

aluminum oxide with colemanite, howlite, priceite, probertite, sassolite, searlesite, and ulexite (the reason for inclusion of ulexite is 

given below) were X-rayed on a diffractometer. In every mixture 

the intensities of the respective aluminum oxide peaks were substantially the same in unheated and in heated materials. In contrast, the 

peaks of the borate minerals were absent in the X-ray patterns of the 

heated samples. Microscopic examination of the heated samples disclosed (1) aluminum oxide and vitrified borate were present in approximately equal amounts in each, ajid (2) no evidence of reaction 

between aluminum oxide and borate minerals was seen.

Priceite and searlesite were run at high sensitivity, whereas all 

other minerals were run at medium sensitivity.
196 CONTRIBUTIONS TO GEOCHEMISTRY

RESULTS

Differential thermal analysis curves for the 13 borates are arranged 

alphabetically in figures 19-25. Each mineral was analyzed three 

or more times. Variations of the results were within the limits of 

the sensitivity of the apparatus. The three reruns were made to 

avoid including any gross error in the data.

In all the curves the vertical scale is the same 1 inch equals 10 

galvanometer divisions. For purposes of comparison, a curve prepared from barium chloride dihydrate, a common reference material 

which illustrates step wise dehydration, is shown in figure 25. This 

compound was selected because it shows large endothermic troughs 

in about the same temperature range as that in which most of the 

borate minerals show their reactions, that is, between 100° C and 

500° C; furthermore, the BaCl2 .2H2O curve was prepared at medium 

sensitivity with a heating rate of 30° C per minute the same experimental conditions used for most of the borate curves. (The trough 

produced by the quartz a-/3 inversion would be barely visible at this 

medium sensitivity setting.)

Five curves obtained from probertite from the Lower Biddy McCarthy mine, Death Valley, are presented in figure 23. Tfye initial temperatures of endothermic reaction 1 vary between 80° C and 90° C. 

The two trough temperatures are essentially the same in all five 

curves; the trough of lesser amplitude was recorded at 140° C, the 

trough of greater amplitude at 260° C. Thus, the precision errors 

in determination of initial temperature and trough temperature for 

this one sample of probertite are considerably less than ±10° C. 

Temperature readings were made at 10° C intervals, the smallest 

readable interval on the thermometer of the portable apparatus.

The initial and trough temperatures (or temperature ranges) for 

the thirteen minerals studied are tabulated below. Data for colemanite are taken from figure 27 ("ulexite 100 percent") as well as 

from figure 21.

Initial temperature Endothermic trough tempera- 

(° C) ture(s) (° C)

Bakerite_-___._____________._.. 400-450____ 580-600.

Borax*___...______________ 50__________ 60, 105-110, 160-170.

Colemanite_____-__-_____--_____- 270-300.____ 370-375.

Ginorite________-______________ 70-80_--__--_- 100, 150,310,360,470.

Howlite--_-_____-____:__________ 450-460- ______ 525-540.

Kernite.--.. ___________________., 100__-__-_---- 185.

Meyerhofferite___________________ 160_-------_-_ 265.

Priceite. ______ ________________ 220-270. ______ 295 2 , 365-385,430-435.

Probertite, ______________________ 80-90--------- 140,260.

Sassolite______-l_____.___________ 120 (?)________ 160.

Searlesite______--_____. _._._._,__ 350__--------- 430.

Tincalcanite________----_._____ r - 60-70-______ 160.

Ulexite-_______________________ 70-90--------- 190-200.

1 Exothermic peak at 75° C.

2 In oae sample.

3 Initial temperature of endothermie reaction id hereafter called initial temperature.
THERMAL ANALYSIS OF BOBATE MINERALS 107

CORKSCREW WASH 

DEATH VALLEY. 

CALIF.

DEBELV MINE 

DEATH VALLEY. 

CALIF.

BAKERITE

DEGREES CENTIGRADE 

900 400

BORAX

DEGREES CENTIGRAM 

100 200

SYNTHETIC

SYNTHETIC

FIOUBH 19. Differential thermal analysis carves of bakerite and of synthetic borax.
198 CONTRIBUTIONS TO GEOCHEMISTRY

T

COLEMANITE

DEGREES CENTIGRADE 

ZOO_______

f

LOWER BIDDY | 

MCCARTHY MINE, 

DEATH VALLEY,

CALIFORNIA

GOWER GULCH,

DEATH VALLEY,

CALIFORNIA

r I T

GINORITE

DEGREES CENTIGRADE 

ZOO 300

I ' 1 I ' I ' I ' I ' I

TWENTY MULE TEAM CANYON, 

DEATH VALLEY. CALIFORNIA

FIGURE 20. Differential thermal analysis curves of colemanite and of ginorite.
THERMAL ANALYSIS OF BOBATE MINERALS 199

HOWLITE

IEES 

300

DEGREES CENTIGRADE

TICK CANYON, 

LAN6. CALIF.

MONTE BLANCO AREAJ 

DEATH VALLEY, CALIF.

KERNITE

DEGREES CENTIGRADE 

100________200

KRAMER DISTRICT, 

CALIFORNIA

FIGURE 21. Differential thermal analysis curves of howlite and of kernite.
: CONTRIBUTIONS TO GEOCHEMISTRY

MEYERHOFFERITE

DEGREES CENTIGRAM

T' i ' T' i ' T' i ' T

MONTE BLANCO 

MIME, DEATH. VALLEY, 

CALIFORNIA

I I I

PRICEITE

OEGAEES CENTI6WDE

f

ZOO 300 400 500 

' I ' 1 ' I ' I ' I ' I ' I ' I

PANOERMA, 

ASIA MINOR

MONTE BLANCO AREA, | | | | | | | | 

DEATH VALLEY. CALIF.

CORKSCREW WASH,) I I I I | I 

DEATH VALLEY. CALIF

FIGURE 22. Differential thermal analysis curves of meyerhofferite and of priceite.
THERMAL ANALYSIS OF BORATE MINERALS 201

PROBERTITE

DEGREES CENTIGRADE 

ZOO 300 400

T F I [

LOWER BIOOY

Me CARTHY MINE,

DEATH VALLEY, CALIE

Same as above

Same as above

Some as above

Some as above

TICK CANYON,| 

LANG. CALIF.

SASSOLITE

DEGREES CENTIGRADE

r

SYNTHETIC

SYNTHETIC

I I

FIGURE 23. Differential thermal analysis curves of probertite and of synthetic sassolite-
202 CONTRIBUTIONS TO GEOCHEMISTRY

GREEN RIVER

FORMATION,

WYOMING

SEARLESITE

DEGREES CENTIGRADE 

200 300 400 SOO

TINCALCONITE

DEGREES CENTIGRADE

100 ___ 200

KRAMER DISTRICT, 

CALIFORNIA

SEARLES LAKE, 

CALIFORNIA

FIGURE 24. Differential thermal analysis curves of searlesite and of tincalconlte.
THERMAL ANALYSIS OP BORATE MINERALS 20$

KRAMER DISTRICT,. 

CALIFORNIA

ULEXITE

T

OEWEES CENTICHAOE

 

200 3OO 4pfl_______900

SALAR OE ASCOTAN, CHILE | I I I I I | I | |

BARIUM CHLORIDE DlHYDRATE 

BaCI2 2H2 0

i ' T i T

FIGURE 25 Differential thermal analysis curves of ulexite and of barium chloride 

dihydrate (BaCl2 '2H2O).
204 CONTRIBUTIONS TO GEOCHEMISTRY

In figure 28 curves of the 13 minerals are presented in order of 

increasing trough temperatures. Similarities between curves would 

make identification inconclusive for the following mineral pairs: (1) 

kernite-ulexite; (2) priceite-searlesite; (3) sassolite-tincalconite.

Borax, whose principal endothermic reaction begins at 120° C, 

decrepitates and expands at about 200° C. Colemanite, whose endothermic reaction begins at 270° C, decrepitates violently between 

350° C and 400° C. Moderately coarse crystalline tincalconite from 

Searles Lake whose endothermic reaction begins at 80° C, decrepitates 

and expands between 130° C and 200° C. Borax, colemanite, and 

tincalconite runs, therefore, were discontinued at 200° C, 400° C, and 

200° C, respectively.

The meyerhofferite curve shows a minor peak at 370° C that is 

probably accounted for by the presence of a minor amount of colemanite (microscopically estimated at 5 percent).

DISCUSSION

In some specimens of the same mineral species variations in the 

temperatures at which endothermic reactions commence and culminate 

are traceable to differences in crystal size. Thus, white powdery 

ulexite from Salar de Ascotan, Chile, shows an endothermic reaction 

which commences and culminates at temperatures significantly lower 

than those for colorless compact ulexite from the Kramer district. 

Microscopic examination of these specimens of ulexite discloses a 

marked difference in crystal size: Ulexite from Kramer is characterized by much larger crystals than ulexite from Salar de Ascotan. 

The crystal size effect is even more pronounced in the curves obtained 

from priceite. Priceite specimens from Panderma, Asia Minor, and 

Monte Blanco area, Death Valley, yielded nearly identical curves; and 

both these priceite specimens are characterized by an average crystal 

diameter of 20 to 25 microns. In contrast, priceite from Corkscrew 

Wash, Death Valley, yields an endothermic trough at 295° C which 

is not obtained from the other priceite specimens. The priceite from 

Corkscrew Wash is characterized by an average crystal diameter of 

less than 5 microns which probably explains this anomaly. Chemical 

analyses, X-ray diffraction patterns, and optical examinations had 

established the fact that the Monte Blanco and Corkscrew Wash 

specimens are of high purity (Kramer and Alien, 1956).

APPLICATION TO SEMIQUANTITATIVE ANALYSIS OP 

COLEMANITE-ULEXITE MIXTURES

Synthetic mixtures of colemanite from the Upper Biddy McCarthy 

mine, Death Valley, and ulexite from the dump at the Eagle Borax 

Works, Death Valley, were prepared in 10 percent increments to test 

the method as a tool for semiquantitative mineral analysis. Every
THERMAL ANALYSIS OF BORATE MINERALS 201;

MIXTURES OF COLEMANITE AND ULEXITE

DEGREES CENTIGRADE 

100 200 300 400

PERCENT 

COLEMANITE 100 

ULEXITE 0

COLEMANITE 90 

ULEXITE 10

COLEMANITE 80 

ULEXITE 20

COLEMANITE 70 

ULEXITE 30

COLEMANITE 60 

ULEXITE 40

COLEMANITE SO 

ULEXITE SO

COLEMANITE 46 

ULEXITE 60

COLEMANITE 30 

ULEXITE 70

COLEMANITE 20 

ULEXITE 60

COLEMANITE 10 

ULEXITE 90

COLEMANITE 0 

ULEXITE 10O

26. Differential thermal analysis curves of mixture's of colemanlte and ulezlte.
206 CONTRIBUTIONS TO GEOCHEMISTRY

5

I 5 

g

u I

40 50 60 

PERCENT ULEXITC

FIGURE 27. Working curve for the semiquantltatlve determination of colemanlte and

ulexite.

sample was mixed with an equal weight of aluminum oxide; 350 

mg of sample was used for each run. All samples were run at medium 

sensitivity. Inspection of the curves in figure 26 reveals the proportional relationship between trough depth and concentration for each 

mineral. A working curve for the semiquantitative determination of 

ulexite (and colemanite by difference) is depicted in figure 27. This 

curve was obtained by plotting the ratio of colemanite trough depth 

(in units of galvanometer deflection) to ulexite trough depth against 

percent ulexite. This method of analysis is recommended because the 

trough depth ratio is considered to be more reliable than a single 

trough depth. In a sense, each mineral acts as an internal standard 

for the other. The. ratio should not be seriously affected by an error 

in weighing of samples.

Four synthetic mixtures of colemanite and ulexite whose proportions were unknown to the analyst were determined by the procedure 

used to obtain the curves in figure 26. The colemanite percentages 

obtained from the working curve in figure 27 are compared with the 

actual colemanite percentages in the columns below.

Colemanite Colemanite 

added (percent) recovered (percent)

50 52

80 84=

10 10

30 37
THERMAL ANALYSIS OF BORATE MINERALS 207

MSREES CEN1HMK

T' i T T'i »T» r-T

ULEXITEI 

KRAMER DISTRICT

COLEMANITE LOWER BIDDY, MCCARTHY MINE

HOWLITEl TICK CANYON!

BAKERITEI 

CORKSCREW WASHtFIGURE 28. Differential thermal analysis curves of 13 boratea.
208 CONTRIBUTIONS TO GEOCHEMISTRY

These results give some indication of expectable precision in this 

analytical method.

It is noteworthy that the trough temperature for ulexite from Eagle 

Borax Works ranges from 155° C for the sample containing 10 percent ulexite (with respect ta colemanite) to 180° C for the sample 

containing 100 percent ulexite. These trough temperatures are not 

directly comparable with those reported for ulexite from Kramer or 

Salar de Ascotan because the latter Were not mixed with A12O3. The 

trough temperatures for colemanite from Upper Biddy McCarthy 

mine vary between 370° C and 385° C; no proportional relationship 

between percent colemanite and trough temperature was noted.

REFERENCES CITED

Alien, R. D., and Kramer, Henry, 1957, Ginorite and sassolite from Death

Valley, California: Am. Mineralogist, v. 42, p. 56-61. 

Faust, G. T., 1950, Thermal analysis studies on carbonates I. Aragonite and

calcite: Am. Mineralogist, v. 35, p. 207-224. 

Hendricks, S. B,, Goldich, S. S., and Nelson, R. A., 1946, A portable differential

thermal analysis unit for bauxite exploration: Econ. Geology, v. 41, p. 64-76. 

Kramer, Henry, and Alien, R. D., 1956, A restudy of bakerite, priceite, and

veatchite: Am. Mineralogist, v. 41, p. 689-700. 

Parker, Carol, Hathaway, J. C., and Blackmon, Paul, 1956, Some curves from

a portable differential thermal analysis unit: U. S. Geol. Survey Bull.

1021-G, p. 237-251. 

Wittels, Mark, 1951, Some aspects of mineral calorimetry: Am. Mineralogist,

v. 36, p. 760^767.

O