SHORTITE, A NEW CARBONATE
SODIUM AND CALCIUM1

OFJosarn J. Fanav,
U. S. GeologicalSurvey, Washington, D. C.
Ansrna.cr
Crystals of shortite, named after Professor M. N. Short of the University of Arizona,
were found in cores of clay shale from Sweetwater County, Wyoming, at depths between
1258 and 1805 feet. The crystals, several millimeters thick, are orthorhombic, hemimorphic, with the axial ratio aibi c:0.455 : 1 :0 648. The indices of refraction are: a: 1.531,
is negative, 75o. Axial plane is [100] with the c axis the acuteF:1.555, t:1.570,22bisectrix. Analyses of two types of crystals give the formula, NarO 2CaO'3CO2.

INrnonucrroN
The mineral describedin this paper, a double carbonate of sodium andcalcium, NazCOr.2CaCOs,was found in a drill core from the test well
John Hay Jr. No. 1, locatedon Governmentland in the SE I of the NW +,sec.2 (1920 feet from N line and 2120feet from the W line), T. 18 N.,
R. 110 W., about 20 miles west of the city of Green River, SweetwaterCounty, Wyoming. The well was drilled by the Mountain Fuel Supply
Co. of Findlay, Ohio, operator, and made available to the U. S. Geological Survey for study by Mr. W. F. Nightingale, geologist, Mountain
Fuel Supply Co. Drilling was started on Oct. 29, 1937,and completed
on Jan. 3, 1938,at a depth of 5323 feet. The elevationis 6355feet. Two
samples from the core at depths of 1594 and 1600 feet, respectively,were sent to Mr. H. I. Smith, Chief, Mining Division, Conservation
Branch, U. S. Geological Survey, in January, 1938, and shown on
chemical analysis by R. C. Wells, of the Survey, to be nearly puretrona, Na2COr.NaHCOa.2H2O.Later other portions of the core, about
30 feet in all, were selected and sent to Washington by Mr. Smith forfurther study, which the writer began in May, 1939. fn the course of thisinvestigation numerous crystals of the new mineral shortite were discovered at several places in the core between the depths 1258 and 1805
feet.
Shortite is named in honor of Dr. Maxwell N. Short, Professorof
optical mineralogy at the University of Arizona, President of the Mineralogical Society of America, and widely known for his contributions
to the study of opaque minerals.
The writer wishes to expresshis thanks to Mr. M. L. Jefierson of theBureau of Chemistry and Soils, Department of Agriculture, who determined that the crystals are pyroelectric, and to Dr. W. T. Schaller ofI Published by permission of the Director, United States Geological Survey.

5t4+.Y,';[SHORTITE, CARBONATEOF SODIT]MAND CALCIUM

515

the Geological Survey who has contributed the section on crystallography.
OccunnBwcB AND AssocrATroN
The first appearanceof shortite in the core is at a depth of 1258 feet.
It occurs intermittently down to 1805 feet, which is the lowest sectionof the core sent to Washington. The matrix is a greenish-grayclay of themontmorillonite type which grades into oil shale. The clay and oil
shale contain pyrite and carbonates of calcium and magnesium, thelatter too fine-grained to determine whether the mineral is dolomite, orcalcite and magnesite, or mixtures. Crystals of calcite up to two millimeters in diameter are abundant in places in the core. Massive trona ispresentat depths of 1325feet and 1587] feet, but is not found associatedwith the new mineral. At the lower depth shortite is present in the claythat overlies the massive trona. The material is from the Green River
formation of Eocene age. The nearly equant crystals of shortite arefrom 1 to 3 millimeters in size, while the tabular crystals are larger, up
to 15 millimeters across and 2 to 3 millimeters thick.
Cnvsrar,r,ocRAPHY
Shortite occurs in individual crystals, orthorhombic, hemimorphic,
and simple in habit, being bounded essentially by only five faces,o(100),o ' ( 1 0 0 ) , c ( 0 0 1 ) , a ( 0 1 1 ) ,a n d e ' 1 0 1 1 )( F i g s . 1 a n d 2 ) . N a r r o w s t r i a t e df a c e s o f o { 0 1 1 } , i n o s c i l l a t o r yc o m b i n a t i o n w i t h t h e b a s e c { 0 0 1} , a r eusually present and line faces of p{nIlwere measuredon one crystal.
All the faces gave poor reflections. Measurements ol e A e' averaged
65"53', hence c:0.648. The average measurementsof four faces ofpt\l1Il, with the crystal set in polar position, gave6:65"57', p:57"21'.
T h e a x i a lr a t i o i s a : b : c : 0 . 4 5 5 : 1 : 0 . 6 4 8 p, o:1.425.
The calculated angles are:c{001}a1100|
el0rrla[ 0 1 T ]plrrllap0000'90 00
00000065 33

90000'
90 00
32 57
32 57
57 26

Two general habits were observed: (1) Nearly equant to short prismatic with elongation parallel to the o-axis (Fig. 1) and tabular parallelto the macropinacoido{100} (Fig. 2).

M,JOSEPE I. FAHEY

Frc. 1 Nearly equantcrystalof shortite.Forms:c{00f}, o{100}' a[011]'

Frc. 2. Tabularcrystalof shortite.
Pnvsrcar- PnopBnrrns
The specific gravity of shortite, obtained by the pycnometer methodat25"C.,is2.629. There is a distinct cleavageparallel to the brachypinacoid 6{010}, which has not been observed as a crystal form. It has aconchoidal fracture and vitreous luster. The hardness is 3. The crystals
are strongly pyroelectric as determined by Mr. Jefferson using Martin'smethod.
fnversion takes place at about 200oC.accompaniedby violent decrepitation. The resulting product appears to be a single compound rather
than a mixture, though it is too fine-grained to permit such a conclusion
definitely to be made. fncongruent melting takes place at about 600'C.
The compound in the solid phase in this melt is probably calcium carbonate, with sodium carbonate, or the one to one sodium calcium carbonate, or a mixture of the two in the liquid phase. When cooled theSHORTITE,CARBONATEOF SODIUM AND CALCIUM517

melt v/as so fine-grained that identification of the component parts bymeans of the petrographic microscope was not possible.
Oprrcal PnopBnuos
The color of shortite varies from colorlessto a pale yellow in reflected
light. rn thin section the mineral is colorless.rt fluorescesa light ambercolor in the ultra violet light from a high intensity mercury vapor iamp.
The indices of refraction at 25"C. are:a = 1 .5 3 1 1+0 .0 0 2
B =1 .sssf

7 :1.570)

Computed from the indices of refraction the 2Y angle (-) is 75".
The crystals are orthorhombic, with the optic axial plane parallel to themacropinacoid and the acute bisectrix normal to the base.
The optical orientation is:
X,a (acute bisectrix) : c axis

Y,p:

@ AXIS2,7 (obtrse bisectrix) : 6 axis
The dispersionis moderate r 1a.
CrrBurcar, Pnoponrrrrs
Samples of shortite from depths of 1649feet and 1729 leet were freed
from the matrix by hand picking. At 1649 feet the matrix is oil shale.
The crystals of shortite at this depth are predominantly equant to shortprismatic in habit. Many of these crystals have small inclusions ofpyrite. The matrix at 1729 feet is a clay of the montmorillonite type.
Most of the crystals of shortite from this depth are thick tabular, parallelto the macropinacoid in habit. No pyrite was noticed in these crystals
but a small quantity of clay was present.
The analyses of these two samples of shortite yield the formula:N a z O . 2 C a O . 3 C O zo r N a z C O a2. C a C O s .
Ane.rvsts ol Suonrrrn r.nolr Dcprr
CaO

Meo
Na:OCO,fnsol.

Per cent
36.34
0.04
79.91
42.90
0.66
99.85ol 1649 FrBr.
Molecular ratioso 64RO')' o+oo:2'oo2o.ooio/o0.s2120.s212:0.991
0 . 9 7 5 00 . 9 7 5 0 - - 3 . 0 0 7

JOSEPH J. FAEEY

518

ANar,vsrsor Suonrrrn rnou Drprn ot 1729Fnm
Per cent
CaO

Mso
NazO
COzInsol.

36.38
0.04
20.07
42.78
0.68

Molecular ratios

00333t'iJ)'**:20 . 3 2 3 80 . 3 2 3 8 : 0 . 9 9 80 . 9 7 2 30 . 9 7 2 3 : 2 . 9 9 8

99.95
The insoluble material was determined by filtration on a sintered glass
filter, drying at 105'C. for two hours and weighing.
Both samples were examined for the following components with negative results:
SO3, Cl, F, SiOr, metals of the RzOs group, SrO, BaO, K2O, Rb2O,
Cs2O,Li2O.
A sample composed of fragments of crystals of shortite that were
free from traces of clay and pyrite was tested in a closed tube for water.
None was present.
Shortite is slowly decomposed by cold water and more rapidly byboiling water. The sodium carbonate goes into solution and the calcium
carbonate remains quantitatively in the solid phase.
The chemical synthesis of an anhydrous soda-lime carbonate with thecomposition of shortite has never been reported, though the compound
NazO. CaO'2COz is known. The writer hopes to study the paragenesisof the minerals found in this core. Such work may do much to reveal
the conditions that prevailed during and since the deposition of thesesediments.

i#