THn AUERTcANM rxERALocrsr
JOURNAI

Vol. 49

GREIGITE,

OF THE MINERALOGICAL

MAY-JUNE,

THE THIO-SPINELSOCIETY OF AMERICA

1964

Nos. 5 and 6

OF IRON; A NEW MINERAL

Bnraw J. Sr<rNxnn,Rrcnrnr C. Eno aNo Fnaxr< S. Gnrlr,lrorl
U. S. GeologicalSurvey, Washington 25, D. C.
Aesrnec:t
Greigite, !'e3S4,occurs as tiny grains and crystals in certain clay layers of the upper partof the Tropico Group, a Tertiary lacustrine sequence in the Kramer-Four Corners area,
San Bernardino County, California. Greigite is cubic, a:9.876+0.002 i+ at 25o C., spacegroup Fd.3m,Z:8, calculated density 4.079+0.003 gm/cc. The strongest r ray powder diff r a c t i o n l i n e s a r e 2 . 9 8 0 A ( 1 0 0 ) , 1 . 7 4 6 L Q D , 2 . 4 6 9 A ( 5 5 ) , 3 . 4 9 2 A ( 3 1 . 5 ) a n d 1 . 0 0 8A ( 3 1 ) .
Greigite is strongly magneticl responding like magnetite to the hand magnet. The mineral
has an ideal spinel structure and contains SFe in site 8a, (| | ]), 16Fe in site 16d.,(i 1 1) and
32S in site 32e, (x r r), rvhere r:0.2505 rvith a standard error of 0 0038. The structure
parameters v,ere refined to a reliabilitl' factor of 9.9%. Greigite is the iron member of thethiospinels, represented in nature by such well-established minerals as linnaeite, polydymite and violarite.
Greigite is named in honor of Dr. J. W. Greig, Pennsylvania State University.

IxrnorucrroN
The existenceof a magnetic iron sulfide with a spinel structure anda compositionin the range Fe3S4
to FezSshas been frequently postulated.
Recent studies b)r Berner (1964), Yamaguchi and Katsurai (1960), andPiggott and Wilman (1958) demonstrate that a magnetic iron sulfide
compound with r-ray and electron diffraction propertiesappropriate fora spinel can be svnthesizedin various ways. Authors, such as Lepp
(1957)and Hutton (quoted by Berner, 1964),have prepareda phasewith
the necessar),n-ra.v properties, but did not recognizethe relationshipto the spinelstructure compounds.Freke and Tate (1961)and numerous
others, have synthesizedmagnetic iron sulfide compounds for whichanalyseshave indicated compositionsin the range Fe+S5
to Fe2S3,
but forwhich, unfortunatell,-,proof of the purity of the analyzed sample by r-ray
or other meanswas lacking.
We have discovered a magnetic iron sulfide with the formula FerSa
and a spinelstructure,in drill coresfrom the Kramer-Four Cornersarea,
San Bernardino County, California, and propose to name it greigite
I Publication authorized by the Director, U. S. Geoiogical Survey.

54+

B. J

SKINNT,R.R C, ERD AND F. S, GRIMALDI(grEg-it)in honor of Dr. J. W. Greig,formerly at the GeophysicalLaboratory, Carnegie Institution of Washington, and now at Pennsylvania
State Universitv, in recognitionof his manl' contributions to mineralogy
and physical chemistrv. The name has been approved by the Commission on New Minerals and Mineral Names. IMA.
(JccunnBNcn
Greigite was discoveredin coresrecoveredfrom lacustrine sedimentsin three test holes drilled in the Kramer-Four Cornersarea, San Bernardino County, California. The location of the wells, known as FourCorners No. 3, 4, and 5, and details of the geology are given b1' Benda
et al. (1960) and by Dibblee (1958). The flat-lying greigite-bearingsediments are Tertiary in age and are unconformabll' overlain by 650 to
800 feet of Recent alluvium. Thel' are unconformably underlain bysandstonesand conglomeratesof uncertain age. The lake beds belong,stratigraphically,to the upper part of the Tropico Group of lliocene(?)
and Pliocene(?)age which were depositedin a former lake about eight
miles east of the well-known Kramer borate district. Although it is notknown whether the former lake in the Four Cornersarea was part of thelarger lake at Kramer, the mineralogvof the borate-bearingbeds in both
Iocalitiesindicates that the lake waters were similar in composition.At
Four Corners, the lake beds are composedof interbedded calcareous
clays, silts and fine- to medium-grainedarkosic sands.
Greigite is found continuousiy through a 1.20-lootsection in holes
3 and 4 and through about 400 feet in hole 5. The heaviestconcentrationsof the mineral were noted in coresfrom the 1700 1701-ftintervai in hole3, 1345-1355-ftinterval in hole 4, and the 1344 1348-ftinterval in hole 5.
Greigite occurs in laminae of grayish-black-coloredsulfide-bearing
clal's and fine silts which are interlaminatedn'ith sulfide-freeclavs,silts,
and sands.The laminae average0.8 mm in thickness,but the greigitebearing layers range from 0.02 mm to 12 mm in thickness. Greigite is
restricted to clav and fine silt layers, being compietely absent from thesandsand other coarse-grainedmaterial.
Minerals associatedwith greigite are montmorillonite, chlorite, calcite, colemanite,veatchite, orpiment, and realgar. The greigite sample
concentratedfor analysis,from hole 5, also contained a small amount of
marcasitein closeassociation.It is noteworthl,'that the oniy' other ironsulfideobservedin the drill coreswas a small amount of pyrite occurring
as disseminatedcrystalsin the interval 843 874 feet from hole 3. Greigite
was not directly associatedwith the pvrite, and was not observedin hole
3 above 1622 feet.
Greigite has also been found in the Kramer borate district as tiny in-GRD.IGITE

clusionsin crystals of kernite on the B-level of the Mudd (old Western
Borax) mine in the southern part of the district. Associatedas included
minerals are montmorillonite, chlorite, biotite, and single euhedral
crystals of dolomite, calcite and searlesite.In contrast to the widespreadoccurrencein the Four Cornersarea, greigite has been positively identified onll- from this single occurrencein the Kramer borate district.
OnrcrxThe alternation of sulfide-bearingand sulfide-freelaminae in thegreigite-bearingsedimentssuggestsvarves and may representseasonalvariations in the compositionand physical conditionsof the lake waters.
Additional studiesof the coresto confirm an annual periodicity have notbeen made.
Freke and Tate (1961)demonstratedthat greigite,togetherwith otheriron sulfides,can be synthesizedby using a culture of the bacteria Deswlphibrio d,esulphuricar.sto reduce iron solutions. The importance ofbacteria in the formation of sedimentaryiron sulfidesis widely accepted
and, consideringthe geologicaloccurrencein the Four Corners area, it
seemsprobable that greigite was formed by bacterial reduction of ironbearing waters in essentiallyanaerobicbottom sedimentsof an alkalinelake. \\iith the exceptionthat laminae containing iron h1'droxideare absent, the appearanceof the greigite-bearingcore is quite similar to thesedimentarl'section (Oppenheimer,1960, Fig. 8, p. 258) from a marine
environment shorvingcolor banding due to bacterial activity-.
In the Kramer district, greigite appears to have formed with borax
in the temperature range 25" to 35o C. (Christ and Garrels, 1959),and
to have remainedas a stable or metastablephaseafter conversionof theb o r a x t o k e r n i t e , w h i c h o c c u r sa t 5 8 o * 5 o C . a n d a d e p t h o f 2 5 0 0 + 5 0 0
f e e t . a c c o r d i n gt o C h r i s t a n d G a r r e l s( 1 9 5 9 ) .
CoNcBxrneuoN AND CuBlrrcel Axarvsrs
Greigite occurs as tin1. grains and crystals evenly dispersed throughout the host clay, to an estimated content ol 5/6 by weight. A partial
concentration of the sulfide was effected by dispersing the clay in wateror acetone and using a magnet to draw the particles away from thenonmagneticcla,vminerals. A further concentrationwas obtained by aheavy liquid separation,but again, a clean separationwas not obtained.
In both cases,considerablequantities of clay minerals and chlorite weretrapped rvith the magnetic grains. Following Neuerburg (1961),we weremost successfulin concentrating greigite by an initial magnetic concentration foilowed by treatments with HF and dilute HCl. X-ray andoptical examination of the final concentrate showed that it contained

546

B. J. SKINNER,R. C. ERD AND F. S. GRIMALDI

abotfi 7/6 marcasite as the only crystalline contaminant to the greigite.
Careful measurement of the r-ray patterns before and after the concentration processdid not reveal any physical changesin the sulfides.
Initial analytic studies to develop suitable microanaiytical methods
and to determine the elements to be analyzedwere conducted on a carefully purified concentrate. Microspectrochemical analysis (Table 1) revealed the presenceof Fe as a major elementwith AI as a significantbut
lesserconstituent. No other elementswere detected in amounts sreaterthan 0.516.
Tasr,o 1. MrcrospncrnocrrEMrcAr Axelvsrs or a CoNcrnrn,ltn
CoNterNrNG
Appnoxnra.rer.v 7516 Gnorcrrn, 10/6 MancasrrE, AND 15/" OrcrNrc Marrsx
Constituent

Percentage

Fe
AI
Cu
Co
Mg
Mn
Na
K
Ni
Si
Ti
F

Major
3
0.1
0.03
0.1
<0.002
0.1
<0.01
<0.05
<0.01
<0.001<05

No other elements u'ere detected.
Analyst, C. L. Waring

From the previously gained experience, approximately 5 mg. of acarefully prepared concentrate,which had been repeatedly digestedin
warm HF and 5/6 HCl, followed by repeatedwashingsin acetone, wasquantitatively analyzed by microchemical techniques. The chemicaltreatment insured the removal of significant amounts of silieate, fluoride,oxide and sulfur phasesas well as any pyrrhotite that might have beenpresent.
Marcasite was isolated by heating the concentratefor 20 hours in(3+2) HCI to dissolve the greigite.l The sulfur in the marcasite wasdetermined turbidimetrically as BaSOqand subtracted from the total
sulfur in the concentrate, determined gravimetricallr'' as BaSOn.Organic
matter was calculatedas the differencebetweenHCI acid insoluble and1 Tests under identical conditions on marcasite ground to an impalpable powder shor,ved
that 1 to l\fp of the marcasite dissolved on heating for 20 hours in (3f 2) HCl.

GREIGITE547

the sum of marcasite plus the ignited aqua regia insoluble. Aluminum wasdetermined colorimetrically with alizarin and iron colorimetrically witho-phenanthroline, to yield the results given in Table 2.
The organic matter, acid insolubles,and soluble AlzOr reported inTable 2 do not reveal their presencein t-ray difiraction photographs of
the initial concentrateand are therefore presumabiv amorphous. The
form of the solubleAlzOr is not known but it is clearly not incorporated
in the greigite becausethe content of soluble Alzos was found to vary
Tl'nt-n2. Cnnurcer,Anll,vsrsol a,5 uc Sm,rpr-n
ol Gnrrcrre
FeSz

7.2%

Acid insoluble, Ignited

5.8

Organic matter

1 3. 0

Solublel Fe

40.3

Soluble S

30.9

Soluble AluOa

12

Soluble CaO
Soluble MgO

<0.5
<05

Total2

98.4

SiOz
FerO:
ALOr
CaO
MoO

none

0.3
J.Z

0.5
0.5

1 Soluble when digested on a steam bath in (3+2) HCI for 20 hours. Ratio Fe/S
:1:1.335:3 000:4.006.
2 Taking soluble CaO*MgO as zero.
Analyst, Frank S. Grimaldi.

between samples,being least in the most carefully prepared concentrates. The formula of the sulf,de,deducedfrom the solubleFe and soluble
indistinguishablein the present studl' from FerS+.The
S, is Fe3.sn6Sa
666,
relative error in the iron determination is estimated as -10.3!6 and of
sulfur as +0.47a.If both of these errors should work in the same direction, the maximum composition range indicated is only FesooSa.oo+ooz.
PnopBnrrBs
Physical ond,optical properties.A concentratedpowder of greigite is sooty
black in color, strongly magnetic and apparently quite stable in air.
Becauseof the small grain size and lack of coherencyin the clay matrix,
we were not successfuiin obtaining a good polished surfaceof greigite
within its matrix, but a greigite concentratewas readily mounted andB. J. SKINNER,R C. ERD AND P- S, GRIMALDI

548

polished in cold setting plastic medium. The concentrate contained
individual crystals ranging from 0.0004 mm to 0.0045mm in diameter,
the median being about 0.0015 mm. Irregular clots and intergrowngroupingsof crystals and grains ranged up to 0.015 mm in diameter.
The small grain size preciuded a determination of cleavage,relative
hardnessand specificgravity. The calculated density, based on r-ray
difiraction measurements,is 4.079*0.003 gm/cc.
In vertically reflectediight greigiteis opaquewith a pale creaml' whitecoior. Against marcasiteit is lessyellow and more pink colored;against
pyrrhotite it is distinctly whiter and less pink. Greigite is completely
isotropic in reflected light. The polishing hardnessof greigite is about
T,qsLE 3. REsuLTS ol HrerrNc Expr,ntunNls oN Gnucrro. Cu,qncrs wexe
Ster-no tN Ev.a.cul.rnn Srr,rca Gr,nss Tueos
Temperature,oc.

Time of heating,
Hours

105
148
198
238
282

90
65
170
165
148

320
395

504
1a

Results

No change
No change
No change
No change
Approximately 5/6 had broken down to pyrrhotite
plus S vapor
Complete breakdown to pyrrhotitefpyrite
Complete breakdown to pyrrhotitefpyrite

the same as that for marcasite,but apparently slightly greater than thatfor p1'rrhotite. A sharpenedsteel needlejust scratchedgreigite,but thetest must be consideredinconclusivebecauseof the small size of thegrains on which the test was made.
Greigite has magnetic properties similar to those of magnetite. The
tendencl' of grains to form clumps and aggregatesduring separation proceduresprobably is due to the magnetic properties.
Thermal'properties.The thermal stability of greigite was tested by heating small fractions of the concentratein sealed,evacuated siiica glass
tubes, the heated product being examined by r-ray and optical means.
The results are presentedin Table 3. No changeoccurredin runs up to
238' C. and the first evidenceof a breakdown occurred at 282oC. in a
148-hourrun, where a small amount of the greigite had broken down topyrrhotite. Becauseno pyrite was intergrown with the pyrrhotite breakdown product, it was assumedthat the excesssulfur generatedfrom thebreakdown was presentas a tenuousvapor phasein the free spaceof theGREIGITE

silica glass tube. Runs at 320" C. for 504 hours and at 295" C. for 17hours showed a complete breakdown of the greigite to pyrrhotite plus
pyrite.
These results cannot be consideredconclusiveevidencefor an upper
thermal stability between 238' C. and 282" C. Clearly there is a kinetic
problem involved and many more runs, and runs of longer duration,
would be necessaryto satisfactorilydetermine the thermal stability andthe temperaturedependenceof the breakdownrate. The results suggest,
however, that greigite, once formed, may exist for long periods undermany natural conditions,provided that it is in an environment shieldedfrom oxidizing agents and fluids in which it is soluble. It is probable,
therefore,that greigitemay be found well back into the geologiccolumn
in suitable environments.
Chemicalproperties.Greigite is very slowly soluble in HF and in warm(3+2) HCl. A dried concentrateof greigite is apparently quite stable inair, showing no tendency to oxidize or decompose.Although its stability
in water has not been specificailydetermined, it rvas observed that asample left in contact with water for three days deveioped a browntarnish, indicating partial oxidization.Although the drill coresweredampwhen first obtained, owing to the circulating muds used in drilling, theabsenceof all solution effectson the associatedborate mineralsindicatedthat the enclosing sediments were effectively sealed off from contact
with ground water by the abundant clay in the section. Some of thegreigite developeda coating of iron oxides after prolonged exposureto
surfacehumidity, but the bulk of the greigite in the coreshas shown nosign of oxidation during the six-year period since the cores were firstobtained.
Etch reaction on the polished surface,using standard etch reagents,
gave the following results:
HNO3, 1:1

Slight etching after 4 minutes. A fe'lv grains tarnished light

trct,1:1

Slight etching of grain boundaries after 2 minutes Drop turned
pale yellow. No tarnish.
Negative, 4 minutes.
Negative, 4 minutes.
Negative, 4 minutes.
Negative, 4 minutes.

KOH, 40% (by rveight)
KCN, 20% (by rveight)
H9CI1.Sc/a (by rveight)
FeClt,20o/n (by weight)

Cnvsrar,rocRAPHY

Morphology. A few grains showed some external cr1,sta1morphology,
but were too small to be separatedfor individual morphologicalstudy.
In polishedsectionabout five per cent of the grains have four-sidedout-

550

B. J. SKINNER,R. C. ERD AND F, S. GRIMALDI

Iines suggestiveof sections cut through octahedra. Unpolished aggregates of grains examined in reflected iight showed only triangular reflecting surfacessuggestingeither tetrahedra or octahedra.Eiectron micrographs revealed forms suggesting both octahedra and, infrequently,
cubes.Thus, although the morphological form cannot be identified withcertainty, the evidence suggestsvery strongly that the predominantcrystal form is the octahedron.
X-ray powder d.ifraction data. The small grain size prevented any successfulatternpt to study greigite by single crystal r-ray'techniques,but
made it an ideal substancefor powder techniques.No grinding or further
handling was necessaryto reducethe grain sizeof the initial concentrate.
Comparison oI the x-ray powder difiraction data with those of Berner(1961) for a synthetic magnetic iron sulfide (Table 4) leaves no doubtthat Berner's material and greigite are the same compound. The close
similarity between the *-ray pattern for greigite and that for the cobalt
thio-spinel,linnaeite, CoaS+,
has already been pointed out by Yamaguchi
and Katsurai (1960) and Berner (1964). Table 4 lists, for comparison,
the r-ra1' data for linnaeite and magnetite (Fe3O+)quoted by Berry andThompson (1962). Although greigite has a considerablyiarger unit cellof indexedthan either linnaeite or magnetite, the direct correspondence
Iines and similarity of intensities serves to emphasize the close correspondencebetweengreigite and the spinels. The increasedcell edge ofgreigite relative to linnaeite is analogousto, and the samemagnitude as,
the differencebetween the cell edgesof the correspondingoxy-spinels,
magnetite and CorO+.
Crystal slructure. On the assumption that linnaeite and magnetite (space
grorp Fd,3m) are isostructural with greigite, the entire powder pattern
can be indexed on a cubic cell with a:9.876 A (Table 4), which compared favorably u'ith the 9.870 A value observedby Berner (1963) for
his s1'ntheticmaterial.
Diffraction intensitieswere recordedwith a diffractometer by mounting the sample in a rvelled quartz holder and making repeated oscillations
along the peaks at a traverse speed of $" 20 per minute. The intensities
were determinedfrom planimetric measurementsof the areasunder thediffraction maxima. The reproducibility of measurement, between different rrrounts, was 4/6. This good reproducibility, together with thesmall grain size,lack of obvious cleavageand equant shapeof the grains,suggeststhat strong preferred orientation was not present and hence
that the observedintensitiescan be used for structure calculationswith
considerableconfidence.
Correcting the observedpowder intensities for multiplicity and apply-

GREIGITE
Tlrln

5Jt

4. X-ney Pownnn DrrlnacrroN D,me ron GnnrGrrn Coup.qnno wrrr Tnosr
lon SyNrnrrrc Fe3Sa(Banxrn, 1964), LrNNaErrE AND MlcNrrrm(Bnnnvexl'froursox,

1962)

d".r" for a cubic cell with a:9.876 A. Measurements made in FeKq radiation, intensities measured planimetrically as described in the text. Intensities of synthetic Fe3Sa
linnaeite and magnetite rvere reported as relative intensities by visual estimation. N.O.
: not observed.

Greigite
I
ucalc

dob"

5 702 5 720
80
3 492 3 . 4 9 8
JI. )2 . 9 7 8 2.980 100.0
2.851 2.855
3.9
2 469
2 470
54.8
JJI
2.266 2.260
t.2
422 2 . 0 1 6 2 . 0 1 7
9.2
333,511 . 9 0 1 1 . 9 0 1
28.6
.l+o
MO
r.746
76.8
669
l.o/l
531
0.9
442
t.@6
N.O.
620
1 . 5 6 1 5 1. 5 6 2 5533
1 . 5 0 6 1 1 .5058
9.8
622
1 .4889 1 .4883
t.)444
1.4255 1.1253
8.6
7 11 ,5 5 1 | 3829 | . 3 8 2 6
o7642| 3197 | 3204
3.6
731,553 1 2857 1.2859 1 2 8800
t.2345 1.2349
9.2/JJ
1.2065 1.2097
0.3
644
1 . 1 9 8 2 1 1975
o.2
R1)
1 . 1 6 3 9 | 1640
0.3
7 5 1 5, 5 5 1 . t 4 M 1 . 1 4 0 1 1 . 8
662
1.1329N.O.
840
1.1042
164
753,9rr1 .0840
0.6842
r.0776
N.O.
664
1. 0 5 2 8
2.1
t.1
93r 1 .0353
844
1 .0080
30.9
111
220
311
222
400

Synthetic,
FeaSr

Linnaeite,
CorS+

d"r,"

dol"

I

5.47
3.34
2.83

2
4
10

2.36

7

209

1.926
1. 8 1 5
1.670

3
6
8

1.712
1.611
1.481
1.416

8
9

2

1.327
1.280
|.261
1.2rl

2
4
1
2

I

r.r75

1
2

1.122
1 .094
1.050

4
8
5

5.70
3.48
2.97
2.85
2.465
2.O12
1 .899i . /+.')

1. 5 6 1
1. 5 0 5

+
o

10
2
8
J

o

9

1.035
1.007

2

I
2

6
5

1.362
1.321
1.260
t.227
1.179

t.tt2
1.090

z

5

1.055
1.036

4

1.005
0.988

1
2

3
8

4.84
2.96
2.53
a

J

7

Magnetite,
Fe:oq

2
J
J

A

A1

6
10
1
7

I

2

No more lines
reportedI

2

5

No more lines
reported

ing the appropriate Lorentz-polarization correction for powder measurements (Buerger, 1960),yielded the F1or,"yin Table 5. With the linnaeite
spinel structure (space group Fd3nt) as a model we placed 8 Fe in the

B, J. SKINNER, R. C. ERD AND F. S. GRIMALDI

552

tetrahedrai site 8o, (+ + *), 16 F-ein the octahedral site l6d, (+, +, +)and32 S in site 32e, (r r r), with r approximately ]. The r coordinate,scalefactor and overall isotropic temperaturefactor were refined by thefull matrix least squares technique. The final results are: r:0.2505,
with a standard error of 0.0038;B:3.2 A2, with a standard error of 0.4
A'. These parametersyield an R factor ol 9.9/6,providing a convincing
Tenr-B 5. CoupenrsoN on OesBnvro eNo Cl.lcule.lrn
lon Gnnrcr:rr

(hhr)

ti,

111
220
311
222
400

.)J.O

153.5
230 8
82.7
425.6
3 5. 0
111.8
N.M.
N.M.
544.8

JJI
/14

333
511
MO
.).tI

JL.Z

0.0
101.8
1 6 1. 9
637
274.8
N.M.
N.M.

442
620
JJ.'

622
444
551
I ll

N.M.:Not

58.1- 164.2-260.3- 23.2428.9- 34.9
118.7
190.3
196 5
5 3 2. 0- 28.40.1
92.0-149.9- 1 1. 9-zJl.92 7. 3- r9.4

642
553

73r
800
,JJ

644
660
822
/Jt

662
840
753
9t1
842
664
931
8M

Srnucrune

Fecrons-/J.J-122.5-116.9
342.8
14.4
0.1
- 594
- 59.31 0 1. 8- 97.r- 11 4175.2- 13.818.1
0.1
485- 8 1. 7
234.9

measured because of overlap or interference.

R:e.9To
B : 3 . 2 + 0 . 4f . edemonstration of the correctnessof the assumed spinel structure. All
bond lengths out to 5 A are listed in Table 6.
The cell data for greigite are:Space group:
Cell dimensions:
Cell volume:
Cell constants:
Density:

Fd.3m,by analogyu'ith linnaeite
A at 25' C.r
9.876+0.002
9 6 3 . 3 + 0 3A 3
8 [Fe:S.]
gm/cc
4.O79+0.002

1 Determined by six successive oscillations across the 440 reflection of greigite and the
331 reflection of Si metal. The sample r.as remade between oscillations. The uncertainty isexpressed as the standard deviation of each oscillation. The cell edge used for Si at 25o C.
was calculated from the data of Parrish (1960).

553

GREIGITE

Crystal chemistry.It is apparent that greigite is the iron member of thefamily of thio-spinelsrepresentedin nature by the well-establishedminerals iinnaeite (CoaSr),polydymite (NieSa),seigenite(Co, Ni)3Sa,violarite FeNizS,r,carrollite CuCorS+and daubreeliteFeCrzSa.
The composition FeeSamakes greigite a polymorph of the recently
described mineral smythite (Erd et al., 1957). Smythite is rhombohedral
with a structure consistingof slabs of pyrrhotite stacked on each otherto give a sheet structure. The measured specific gravity of smythite is
4.06, very close to the density oI 4.079 gmf cc calculated for greigite.
This similaritv is to be expectedbecausesulfur atoms in both structures
T,qBln 6. BoNn LnncrHs rN Gnnrcrru our to 5A
Bond
lengthA

From

0.2505,0.2505) s(0.2505,-0.0005, -0.0005)s (0.2505,s(0.2505,0.4995,0.4995)s(0.0005,0.2495,0.5005)
0 1250,0.1250)
Fe(0.1250,
0.3750)Fe(- 0.1250,0.3750,
Fe(0.5000,
0 2500,0.2500)
0.5000,0.5000)
Fe(0.5000,
Fe(0.5000,0.0000,0.0000)

3.508
3.480
3.49"
z.t+8

4 09s
2.466
4 . 2 7o
4.282

Multiplicity
3
J

6
4
t2
o

2
o

0.1250,0.1250) Fe(-0.1250,-0.1250, -0.1250)
Fe(0.1250,
Fe(0.5000,
0.2500,0.2500)

4.092

16
24

0.7500,0.7500)
Fe(0.5000,0.5000,0.5000) Fe(0.5000,

3.49r

12

occur in nearly ideal closely-packedarrays-smythite as a combinationof hexagonai and cubic closepacking and in greigite as cubic close packing-which should lead to almost identical densities. The iron atoms inboth structures are distributed between the possiblesites in such a waythat they do not cause any significant distortions in the closely-packed
arra'S'
Drscussrou
Successfulsynthesesof a phase which is obviously greigite have beenreportedby Berner (196+),Hutton (quoted by Berner, 1964),Yamaguchi
and Katsurai (1960),Piggott and Wilman (1958),and Lepp (1957).Probable syntheses,but Iacking sufficient data to justify certain identification,
have been reported by many others.
Lepp (1957) identified his synthetic product, later shown by Berner(196a) to be identical with greigite, as melnikovite. Doss (1912 a, b)

.554

B. J SKINNII.R,
R C. nRD AND F. S. GRIMALDI

originaily describedmelnikovite as a magnetic form of FeSz,solubie inwarm dilute HCl, with a specificgravity about 4.2 to 4.3 and hardnessof
2 to 3. It is possiblethat the type melnikovite may contain somegreigite,
as suggestedb1' Berner (1964), who remarked that it was probably a"finelv intergror'r,nmixture of elemental sulfur and one or more of thefollor,vingmagnetic iron sulfides: pyrrhotite, smythite, or the cubic
FeaSr. . " . The originai identification of melnikovite remains so uncertain, and the descriptionso unsatisfactoryand incomplete,that it isunwise to atternpt to use the name for a well-definedspeciesIike greigite.
X-ray diffraction data have recently beenpublishedby Korolev (1958)
and Volkov (1961) for natural materials which they called melnikovite.
Korolev's material occurredas a finely dispersediron sulfide in a Tertiarv sediment.The r-ray pattern of this substancedoesnol match thatof any knorvn iron sulfide, nor any mixture of known iron sulfides. Volkov's (195i) material occurredas biack, magneticiron sulfideconcretions
at a depth of 3.5 metersin the Black Seasediments.Analysis of the concretions gave a composition of FeSraowhich is ciose to the FeSr.eaof
greigite. The r-rav diffraction pattern, as recognizedby Berner (1964),
indicated a mixture of tetragonal FeS (recently describedas the mineralmackinawite by Evans et aI., 1962) and greigite, with greigite as the
major phase. Volkov's observation appears to be the first un'equivocal
observationof the natural occurrenceof greigite.
Follorving completion of the present study, and while this paper wasin press,the article "Melnikovite as a mineral species"by A. P. Polushkina and G. A. Sidorenko was published in Zapiski Vses. Mineralog.
Obshch,.,92, 5+7-551, 1963. The article was very generousll,'translated
for us by our colleagueMichael Fleischer.
Polushkina and Sidorenkoclearly establishedthe existenceof an ironsulfide mineral which is identical with greigite. We disagreewith theirassignmentof the name melnikovite however, for the reasonsoutlined.
The uncertaintl' as to the identit_vof Doss' originai melnikovite remains, and for this reason the Commission on New Minerals andMineral Names, International Mineralogicai Association,approved thename greigitefor the thio-spinelof iron.
Acr<Nowr,BlcEMENTS
We are greatly indebted to our colieaguesDaniel E. Appleman, forassistancewith certain crystallographiccomputations, and Howard T.
Evans, Jr., for several helpful discussionson crystal chemistry.
RnrnnnNcos
BnNoa, W. K., R. C. Em aNo W. C. Snrrn, (1960) Core logs from five test holes near
Kramer, California. Lt. S. Geol.Srtrtey Bull. lO45-E.

GREIGITE
BrnNnn, R. A. (1964) Iron sulfidesformed from aqueous solution at lot' temperatures andatmospheric pressure. Jottr. Geol., in press.
Bnnnv, L. G. aro R. M. Tnoupsox (1962) X-ray porvder data for ore minerals: The Peocock Atlas, GeoI.Soc. Am. Mem.85.
Buoncnn, M. J. (1960) Crystal-structure Analysis. John Wiley and Sons, N. Y.
Cnnrsr, C. L. ar.rnI{ M. Gannnr.s (1959) Relations among sodium borate hydrates at the
Kramer deposit, Boron, Caiifornia. Am. f our.Sci,.257r 51G528.
DtRrr.nn, T. W Jn (1958) Geologic map of the Boron Quadrangle, Kern and San Bernardino Counties, California. U . S. GeoI.Suney Mineral, Imest. Field Studies Mop MF-204.
Doss, BnuNo (1912a) Uber die Natur und Zusammensetzung des miocinen Tonen derGouvernements Samara auftretenden Schwefeleisens.Ifezres-f ahrb. Mineral'., Bei,I. Bd'.,
Abt. A,33,662-713.
--(l9l2b) Melnikor,vit, ein neues Eisenbisulfid, und seine Bedeutung ftir Genesis derKieslagerstritten. Zeit. prokt. Geol,.2O, 453-483.
Enn, R. C., H T. Evexs, Jn. axn D. H. RrcnrBn (1957) Smythite, a ne\\-iron sulfide, andassociatedpyrrhotite from Indiana. Am. Mi.neral.42t 3W-333.
Evaxs, H. T. Jn., R. A. BnnNnn aNo Crr,q.nlrs Mrr.roN (1962) Valleriite and mackinawite.
Geol,.Soc.Am. Frogrom 1962Ann. Meet ,47a.
Fnnrr, A. M. eNo DoN,rr,n Tera (1961) The formation of magnetic iron sulfide by bacterial reduction of iron solutions. Jour. Biochem. ond' Microbi'ol. Teehn. and Dng.3,
29-39.
Konor.nv, D. F (1958) The role of iron sulfides in the accumulation of molybdenum in sedimentary rocks of the reduced zone. Geochemistry (English translation), 1958 (4),452463.
Lner, H. (1957) The synthesis and probably geologic significance of meinikovite. Icoz.
Geol'.52,528-535.
Nnunneutc,
G. J. (1961) A method of mineral separation using hydrofluoric acrd. Am.
M i n e r a l .4 6 , 1 4 9 8 - 1 5 0 1 .
OrrnNuntrnnn, C. H. (1960) Bacterial activity in sediments of shallorv marine bays. Geochim. Cosmochim.A cta.. 19. 244-260.
Pannrsn, W. (1960) Results of the L U. Cr. precision lattice-parameter project. Acto Cryst.
13, 838-850.
Prccorr, M. R. aNn H. Wrr-uaN (1958) The sulphiding of mild steel surfaces. Acto Crysl.
11,93-97.
Voxov, I. I. (1961) Iron sulfides, their interdependenceand transformation in the BlackSea bottom sediments. Trud.y. Inst. Okeanol,.Ahail. N auk SSSR. 50' 68-92 (in Russian).
Ymr,reucnr, S. eNn T. K,trsunlr (l96}i) Ztx Bildung des ferromagnetischenFqs4. Kllloi.d
Zeit. l7O, 117-148.
Mant+script receiteiJ Not:etnberB, 1963: accepted,
for publication, Notember 22, 1963.