THE CRYSTAL STRUCTURE OF MARCASITE
M. J. Buonctn, MassachusettsInstitute of Technology.
ABSTRACTThe only attempts to investigate the crystal structure of marcasite have been
made by Huggins and by de Jong. Huggins' contribution has been of the nature ofguesswork. The structure proposed by him on t-hebasis of Lewis' atomic theory ulti
mately proves correct, alttrough his crystallographic substantiation of it is fortuitousand incorrect. De Jong, who attempted the only *-ray work on marcasite, arrived
at dimensions for the unit cell similar to those given beyond, except that his o-axis
is doubled. He gave I//1 as the space group.
In this paper, the details of a complete r-ray determination of the structure of
marcasite are given. No essential assumptions have been made other than that marcasite is holohedral. The rotation and oscillation method of analysis was alone used,with the crystal completely bathed in molybdenum Ka radiation. The determination leads to the following structure for marcasite:
Unit cell:

a:J.J7A

b:4.M hc : 5 . 3 9A
Space group:

Vn12

Iron atoms (on symmetry centers) at: [[000]l and ttiiill
Sulfur atoms (on reflection planes) at: llOuaa"lJ, lfofr'tn"ll,

wherelli, L-ur, t*o"ll, andll+,++ub'+-t)"ll.2o3t.0r
[u:
1
+ .01
[0,: .375(Conventional marcasite orientation, origin at a symmetry center).
There is no complete agreement among the authors giving analytical expressions
or equivalent positions of l/ntz. 1'ht equivalent positions are therefore rederived. It
proves that Schiebold gives incorrect positions for symmetry centers and screw axes,
and that Mark gives an incorrect origin of coordinates for the equivalent positionsof this space group.
Marcasite possessesa 6-3 coordination structure. It is made up of units essentially equivalent to units discernable in the pyrite structure. Pyrite has a difierent
linking of tle groups which is also consistent with 6-3 coordination. The rutile structure is a special case of the marcasite structure, and the rutile and marcasite groups
display a very similar crystal habit.

361

362

TH E A M ERICAN MI NERALOGISTMarcasite appears to be comFosed of iron and suUur in the atomic state. Bothkinds of atoms have almost identical radii, 1.12 A.

TABLE OF CONTENTS
Page

Lrrrnnrur-n.
Merrnrar,.. . . .
Tur Ullrr Cur,.. .
Trn Spacr Gnoup
Indexing. . .
Determination of SpaqeGroup.
Equivalent PositionsoI Vnrz.. . .
PossibleArrangementsfor Marcasite.
fNrrNsrry Consrnr:nerroxs
PhaseFunction of I/7,t2
ReflectionIntensities.
Elncrrrerror or Ileossrsm Mancesrrr Srnucrunrs.
fntensityComparisons.. ..
The Marcasite Structure. .
DrmnluN.lrroN ol P,rnamrnns
Thl Mencesrrr Srnucrur_n.
Description.. . .
GeometricalProperties.. .,Rolerror.r ro OrEDRSrnucrunns. . Pyrite... . .
Rutile .. . .
Tsn Cmurcar Nerunn ol Mencasrrn.
Radii of Sulfur and Iron Atoms.
State of Ionization. .

Acxmowr,rtcBlreNr.

362
365
366
370
370
s70
372
3v6
377
377
J/6

380
380
381
381
387
J6/

391
392
392
392
393
393
394
395

LrrBnerunr
Since almost the beginning of the period of crystal analysis withaid of r-rays, the structure of pyrite has been known. Indeed it
was the first crystal speciesanalyzed,rall of whose atoms were not
fixed by symmetry. The structure of its polymorph, marcasite,
however, has continued to remain unknown, although it has beenguessedat, and an attempt has made to deduce itby r-ray means.
Believing that the Lewis theory of the structure of the atoms
required the linking of sulpher and iron atoms to be the same inpyrite and marcasite, Huggins2presented a structure for marcasite
I W. Lawrence Bragg, The Analysis of Crystals by the X-ray Spectrometer:
Proc. Royal,Soc.Lonilon, (A) 89, 1914,pp. 476-478.
' Maurice L. Huggins,The Crystal Structuresof Marcasite (FeS), Arsenopyrite(FeAsS),and Loellingite (FeAsz):Physical Ret:iew,(2) lg, 1922,pp. 369-373.

IOT,IRNAL MINERALOGICALSOCIETY OF AMERICA

363

Huggins.ftoJ

Frc. 1A, Huggins' Fig. 1A veryslightly modified: the arrangement ofiron atoms about the S-S group in pyrite.

Fro. 18. Huggins' Fig. 18, veryslightly modified: the arrangement ofiron atoms abo.rt the S-S group in marcasite. The directions of the conventional marcasite axes are shown in comparison with those deduced by Higgins.

Frc. 2. Huggins' Fig.2, somewhat modified, illustrating the orthorhombic structure resulting from continuing the arrangement implied in Fig. 1A.

364

TH E AMERTCAN M I N ERA LOCIST

based on a rearrangement of major units of the pyrite structure.
Since the structure so deduced has actually proven to be correct,
Huggins' figures are reproduced here. It should be pointed outthat Huggins' crystallographic substantiation of this structure istotally incorrect.
Fig. 1A illustrates the arrangement about the S-S group in pyrite. By reorienting this group undisturbed, as in Fig. 1B, and linking the groups as in Fig. 2, an orthorhombic structure results. The
rearrangement of groups leaves the requirements of Lewis' theory
satisfied.
In attempting to justify this structure, Huggins' argument isthat the axial ratio of marcasite given by Allen, Crenshaw, Johnston, ahd Larsen,snamely 0.7646:.l;I.2176, is consistent with ther a t i o o f l e n g t h sA B : A F : A A t , F i g . 1 B . H e n c e ,h e d e c i d e s t, h e s ea r e
the directions of the a, b, and c crystallographic axes, respectively.
Since the unit cell, Figs. 1B and2, is double the length of ,4.Bin the
direction of this line, the true axial ratio of marcasite, Huggins concludes,should be 1.5292:| : 1.2176.
The fact is, however; that Huggins does not have the correctorientation. The r-ray work to be described later proves the sulfur
atoms to occupy (100) planes, hence, Huggins' b is equivalent tocrystallographic a. Trial calculation indicates that the axes must
transform as follows:
Hugginsbo2aCrystallographic
is actuallyis actuallyis actuallyobUsing the axial ratio data adopted by Huggins, his axial ratioc :a:bo: h .r.

or'822: 1:
t.s2g2: i : t.zizo shouldactuallvb" ti.,zt zo: t.s"zsz,1.256, which is fairly close to the marcasite ratio. In other words,
Huggins' incorrect, apparent substantiation for the proposed
structure depends on the fortuitous relation between the marcasiteaxes:
a : b ' c. = b : c : 2 a
3E. T. Allen,J. L. Crenshaw,
JohnJohnston,andEsperS.Larsen,Die mineralischen
Eisensulfrde:
Zeit.Anorg.Chemie,76,1912,p.254.
Thisis equivalent
to themorefamiliararticlein Englishby the authors: Am. J. Sc.,(4) 33, 1912,p. 221.

JOURNAL MINERALOGICALSOCIETY OF AMERICA

36s

The only experimental attempt to determine the structure of
marcasite has been made by de Jong.a De Jong attempted to analyse a crystal of marcasite from "Bohemia," with Fe-K radiation
using only the powder method.s He also partially investigatedother minerals of the marcasite group by both powder and rotating
crystal methods. His results may be summarized as follows:

Axial lengthsof unit cell

Formulaweights
per unit
cell

Space
group
Calculatedl

Literature

4.86 14.85-4.90
De Jong did not attempt to complete the structural determination.
MarBntarAtl of the writer's experimental work was done on crystals derived from a single hand specimen.Although unlabeled, this was oneof the familiar Joplin specimensshowing a thin chert sheet on bothsides qI which had grown deep wine-colored sphalerite crystals,
which in turn, had acted as a focus for the crystallization of marcasite. This particular specimen was chosen because its marcasite
crystals, on the whole, were homogeneous, easily oriented, andprovided untwinned individuals.
The marcasite crystals themselves were of diamond shaped,
tabular habit, flattened parallel to {OOt} . fne diamond shape wasoutlined ty { ttO}. The basal pinacoids were not actually present,
but were representedby slightly warped, highly striated surfacesof
this altitude, produced by vicinal brachydome striations. None ofthe planes of the striations were identified with certainty, but someof the { 110} planes gave fairly good signals. The average of several
measurementson one crystal gave:(110)n (110):r05"42',from which it follows : a: b : .7577 : I{ W. F. deJong, Bepaling van de absolute aslengten van markasiet en daar-mee
isomorfe mineralen: Physica,6, 1926, pp. 325-332.
6 Op. cit. p. 329 and p. 331.

3ffi

THE AMEMCANMINERAINGISTA personal determination of the density on about .Z gram ofcarefully hand picked, crystal fragments of this material gave avalue of 4.919at 28' C.
Delicate qualitative6 determinationsTon a total of about .8 gramof this marcasite indicated that nickle and cobalt (elements to be
expected as possible constituents replacing some iron) as well as
antimony,arsenic, and bismuth (to be expectedas possiblereplacersof some sulfur) are absent. Incidentally, lead and copper were also
found to be absent. Allen, Crenshaw, Johnston, and Larsen8 foundthe marcasite from Joplin to be of ideal FeSzproportions. Doelterand Leitmeyere quote an analysis of Missouri marcasite by E.
Arbeiter which also indicates ideal FeSz. The marcasite used in the
structural determination, therefore, may be regarded as perfectly
suited for the establishment of a new crystal structure type.
The absorption coefficient of marcasite is high, consequently
relatively minute splinters were used in the r-ray determinations.
Three crystals were used, mounted for rotation about tt;e a, b, and.
, axes, respectively. Because of the poor but real cleavage along
I 1101, the c axis splinter was most nearly of uniform crosssection,
and was used for most of the intensity comparisons.
Tnn UNrr CBr.r,
All r-ray work was done by means of the rotation and oscillation
methods, following Bernallo rather closely, with the crystals completely bathed in molybdenum Ka radiation. The axial lengths
were determined by rotating the crystals about the three crystallographic axesand recording the reflection on 31X4-1 inch glass
6 I was prepared to have quantitative analyses
made, but our best profqssional
analysts (including Miss Mary G. Keyes and the new laboratory for rock ahalyses
in charge of Dr. Grout of the University of Minnesota) declined to make them,pleading inadequate equipment for sulfide analyses. where can one obtain reliablesulfide analyses? My own experience with the routine commercial analyst is that he 'cannot be relied upon for scientific work.
? G. G. Marvin, analyst.
8 E. T. Allen,
J. L. Crenshaw, John Johnston, and Esper S. Larsen, The Mineral
Sulfides of Iron: Am. -1. Sc., (4) 33, l9l2,p. l7T.
e C. Doelter and H. Leitmeyer, Handbueh
der Mineral,chem.ie, Bd. fV, Erste
Halfte, Dresden and Leipzig, 1926, p.567, analysis 8.
1o D. Bernal, On the Interpretationof X-Ray, Single Crystal, Rotation photoJ.
graphs: Proc. Royal Soc. Lonil., (A) lf3, 1926, pp. ll7-|ffi.

JOURNAL MINERALOGICAL

367

SOCIETY OF AMEMCA

plates at a distance of about 6 cm. from the crystal. llhe following
valueswere obtained:o : 3.374
b : a.MLc : 5.394
In view of the fact that de Jong had already published an o-axis
length about double that just given, special attention was given to
the possibilities of an error in this determination. Of course,it iseasy to overlook half-spaced, odd value, layer lines, and usually
any mistake made in obtaining axial lengths is in the direction of
missing these and obtaining halved axes. It is quite certain, however, that none of these appeared in any of the writer's photoAxr,u,Retror-ray determination
goniometricdetermination
Goldschmidt'saveragell
Larsen' syntheticlz

DensitYa:b:e
4.91.759:I:1.214
calculated from r-ray data
4.92
actuallydetermined.758:1:?
.758:l:1.212'7646:l:l '2176
4.g5-4.90
Dana,s ransegraphs. These photographs include not only ordinary rotation
plates placed at a distance of about 6 cm., and exposedabout 17
hours, but also longer exposuresof 40 hours, both at about 6 cm.
with flat plates, and at about 5 cm. with cylindrical film. None of
the 17 hour exposure, 15o oscillation showed any indications of
missedlayer lines, and, finally,every reflection was indexed without
difficulty, none requiring a halved a-axis reciprocal lattice (i.e.,a doubled o axis in the spacelattice).
The number of formula weights of FeSz associated with a unit
cell may be calculatedas
Volume X density
Formula weightX l.64Xl0-24(3.37){4.44X5.39) X ro-24X-4.92:2.03,

119.96X r.64X-tO-24
indicating two formula weights per unit cell.
11From Victor Goldschmidt, Winkeltabe!\en,Berl'in, 1897,pp. 232, for which
Goldschmidt says (page413), "The elementsdifier strongly accordingto various
observers.The mean of the data by Miller, Sadebeck,and Gehmacherare given."
12E. T. Allen, J. L. Crenshaw,John Johnstonand Esper S. Larsen,The Mineral
Sulphidesof Iron. Am. J. Sc.,(4) 33, 1912,p.221.

368

TH E AMERICINMIN ERALOGIST'Ihe,valuesof this axial ratio and the density calculatedfrom it
are in good agreement with the goniometrically determined ratio
and the direct density determination shown in table on page 367.
The differencesbetween the axial ratios given and those foundin the literature need not be dwelt upon. The axial ratio is unquestionably a function of the composition. The check between
Goldschmidt's average and my own values is probably fortuitous.
T.q,sr,B I
Catalog of Planes Indexed
Pinacoids

hrn

00t

200

oo2

400

040

600

060

006

Prisms and domes

510

110

240
hh0

150

7r0

MO
550

J50
260

460

190
l0t

701,or

7rr
202

h0t

103

402

303

602,or6t2

503
604, or
614

105
011
ol2
013

0r5

505,or

o2l
o22
023
o24
025

031
o32
033

041
042
043
044
045

053
055

061
062
063
064

07r
072
084
084

JOURNAL MINERALOGICALSOCIETY OF AMEMCA

369

Tlnr,r I (Contd'.)
Catalog of PlanesIndexed

tzl
122
L23

141
'142
r43
145

165
26t
262
263
264
265

152

22r
222
22s
224
225

23r
232
233

24r
242
243
2M
24s

253

I3 1 1

szL
322

331
332
333
334

341
342
343

352

3hl 1st3

lst+
421
422

43I

424

fstt

534

63r

t-

ot 622?
1612,
1ffiz
6ht I
| 613
1614,or 624

Ioo+[71], or
'"
\'o'

44r
M2
M3
44
M5

s2r
532

721,or
7tl

271
282
2U
381

36t
362
363
374

345

[31s

181
r72
164

[2rt
l2r2
zkt l2r3
l-_
[zrs

Istz

t6r
t62
163

131
132
133
134
135

542
543

JOJ

471
462

453
455

370

THE AMERICANMINERALOGISTTHE SPACE GROUPINDEXING.Following Bernal,13 the planes giving rise to reflections
have been indexed by allowing the crystal to oscillate through definite 15° ranges, with an overlap of 2° between range settings. Setsof photographs were thus made for oscillations about the a, b, and caxes, recording being accomplished on flat plates at about 6 em.
crystal-to-plate distance. The planes so indexed are listed in heavy
type in Table 1. The chance of mis-indexing among these planes isvery slight, for most of them appeared on all three axial sets of oscillations, and were therefore checked twice, while all but a very
few appeared on at least two axial sets of oscillations.
In order to fix the sulfur parameters more closely, it was necessary to obtain reflections from planes of higher index than those recorded on the 3t X 4t plates at about a 6 em. plate distance. For
this purpose, a complete new set of oscillation and rotation photographs was made using a cylindrical camera of about a 5 em. radius. All plates so indexed are listed in Table I in ordinary type. It isbelieved that the indexing is correct except for possibly some of thevery high index planes where the oscillation range aUowed a choice
between two possibilities. In most cases, the doubt and choice havebeen indicated in the table.
The plane 006 alone was indexed from a complete rotation photograph by correlation of reflection sequence.
DETERMINATIONOF SPACE GROUP.An analysis of the recorded
reflections indicates that all classes of pyramid planes (hkl) arepresent regardless of the values of h+k, h+l, k+l, or h+k+l.
Hence the space lattice can not be (OOl)-centered, (010)-centered,(100)-centered, face-centered, or body-centered. It must therefore
be the simple orthorhombic lattice roo This eliminates all orthorhombic space groups except:
C2vl_C2vlO, Vl- V\ Vhl- Vh16,
by reflections actually appearing.
Of the pinacoids, prisms, and domes, the reflection of the foUowing classes of plap.es only are absent:(a) (hkO) when h+k is odd(b) (hOl) when h+l is odd
13op.

c-it.

JOURNAL MINERAINGICALSOCIDTY OF AMERICA

J/

I

Origin

,(z)
ilY)
Space
Group
Frc. 3. Perspective view of space group tr/r,12,
with both conventional space grouporientation and conventional marcasite orientation indicated. The symmetry elements are as follows: horizontal reflection planes; vertical glide planes with diagonal
glides; vertical 2-fold rotation axes; horizontal 2-fold screw axes; and syrnmetry
centers.

Fro. 4. Projection of some of the symmetry elements oI V n12
on the lower reflec*tion plane of Fig. 3, illustrating the derivation of the coordinates of the general
position by the use of the reflection planes, the (010) spacesroup diagonal glide
planes, and 2-fold axes.

372

TIIE AMERICANMINERALOGIST(c) (h00) when Z is oddl(d) (0k0) when fr is odd I specialcasesof (a) and (b)(") (@l) when I is oddj

Reflection of all other classesof planes are present. This eliminates
all of the above spacegroups except:
Cz,r, Czr7,C2,ro,VrrVzrV',V4,V612,Vf3,
by reflections actually appearing.
In the rather complete list of reflecting planes available, noclassesof planes (a) and (b) appeared, in spite of the fact that thedimensions and setup of the apparatus would have recorded, if
present and if sufficiently intense:
at least 23 of the class (hk0) where h*k is odd, including thespecial cases.
at least 17 of the class (h0l) where h*I is odd, including thespecial cases.
It may reasonably be concluded, therefore, that these planes areabsent because the classesare absent, and not because of some
fortuitous condition. This eliminates 4ll spacegroups but Czoloand
Vf2, boLh of which have absent classesidentical with those observed. Czolois hemimorphic, so, granting marcasite is holohedral,its space group is tr/112.
In order to transform from the conventional space group orientation to the conventional marcasite orientation, the o and c axes
are interchanged, together with the corresponding h and I indices.
Eeurvar,Br.rr PosrrroNs or Vnr2. A perspective view of spacegroup I/r,12is given in Fig. 3. In Fig. 4, some of the elements of thegroup are shown projected on the lower, horizontal reflection planeof the perspective view of the space group. By introducing an assymmetric exploring "molecule" in a general position, the multiplication of this general "molecule" by the symmetry elementsof thegroup can be studied for the purpose of derivingthe equivalent positions of the group.
For coordinates,it is convenient, for x-ray intensity work, to usephase angles, in terms of which the length of any axis of the unit
cell is 360" or 2zrrhalf.the length 180oor z-, or, in general, any portion of the length is d,. The origin of coordinates used here is a symmetry center. By placing the "molecule" IRu in a general position,

SOCIETY OF AMERICAJOURNAL MINERALOGICAL

J r.)'I'ableII' Other elethese elements reproduce it as indicated inments than the particular ones chosen as generators in the tables
could be used for deriving these equivalent positions' The symbols used in the projection can be comprehended from the fol'molecule', which islowing illustration: dRd signifies "the 6th
Right handed, and pointing down". It is convenient to conceive of"molecules" I,2,3, and 4 as being clusteredabout the origin [[000]]
and associated with the lower horizontal reflection plane, and of"molecules" 5, 6,7 , and 8 as being clusteredabout [[rrr]l=fi$i]]l
and associatedwith the next plane above. The dotted "molecules"
are below the plane with which they are associated,the others are
TasLE II.
DrnrvarroN

Symmetry
operation

ol CociaorNerss or Gnrtenar PostrroN ot V*toperated
upon

Designation of
resulting"molecule'

Coordinates of resulting "molecule"Spacegrouporientation

Marcasiteorientation

originall[e"ebosl

llofizodl
Vertical2
rotation axis
through
Lower, horizontal reflection planetlsioi"lllo"obPf,lllofiziz1l
Vertical glide
plane witl

n|lb

r-02, t-1sl

r-Ln,

r-1u

r*lf,fr-0en102, r-

r-0o,

rlfiu

n'flo]ldiagonal

327Lu

ln-01, r!02, r!03]
nllu

r-02,

rlls]

fn*0", r*0u
rl0o, r-06, rf1"ll374

TH E AM ERICAN MINERALOGIST

6ln-.Y

d

d

EEH:E
g
5
'f O H*F€'r p tr.9
r d o'd

\r{
=

5'n

(€

zE28

H

a
cd

l=*
irN
u

= = i l N

S
-lS

trr

iid

F

r'l^

"lS o E'
dlN

:i

itN

j *

:

itd
^

C)

A

O
O

i-a

drn
ilN

OAR
*lN O

-

==

.-i.-!

a

€o

F
@

o

z

|
ilN

|

s

.!_?
A,ei
a

+l
F
^

F
-

6
E
Ots

SSe-.':=l-i-

6E

==

OF
ots

>t

o

a

'.1
Fi

bo(q
9li
cd.:

sto_
sLs

ts ts
: j.

OF

oh
ots

-.l-l

<i

cO

-r -r

rS.4aoN

N+\or

HN4\O

do4\o

++++

++++

N<r\ooo

++++

ON

++
N\O

++

<r@

-r -r

or
T-r

N\O

++

<r oO

$oo

+
+
N\O
++

N\O

+
+
aQr

+
+
rDN

++
++

a
o

N=

.ts h

:o

N :

: @

U) ^-.

:E

^X

"qq
5?.

=r"l x.; =

oO

o d=
=!Y

>
: !

-x
I

f,x
a --

ov

iX
a!

Q€

ai
=l

=i

E'

;z -

:x

i^h

o9
=o
r?tr
qtr

=o
= F

.v

>l

ET

JO\]RNAL MINERALOGICALSOCIETY OF AMEMCA

J/J

above the plane. By putting the exploring "molecule" lRu, on theseveral symmetry elements of the spacegroup instead of in a general, symmetryless position, it coalesceswith one or more of its
above seven derivatives, giving rise to the special positions listed inTable III.
A discussionof the space group and its equivalent positions has
been given in some detail, for the following reasons:
1. In the most complete table of equivalent positions, that of
Wyckofi,ra there is no explicit meansof knowing, so far as I can discover, what point has been used as the origin of coordinates' Thismay be obtained by a study of Wyckofi's figures, but only after the
space group itself has been thoroughly visualized from some othersource. When this has been done, the coordinates can be easily
written down by inspection.
2. Mark, who published a list of equivalent positions,ls lists
positions identical with Wyckoff's, giving as the origin a symmetry
center. This is incorrect. Both Wyckofi's and Mark's origins areevidently on 2-fold rotation axes halfway between symmetry centers. Hopeless confusion results if Mark's stated origin is relied
upon for the deductions given beyond.
3. Schieboldrogives his origin of Vntz as "on a twofold axis ll[001] in intersection with a reflection plane ll (001)," i.e., on a symmetry center. He gives correct analytical positions of the reflection
planes, glide planes, and 2-fold axes,but then fails to give any symmetry center at the origin or in equivalent positions. In fact,
Schiebold's symmetry centers and screw axes are incorrectly Iocated. Needlessto say, this representation of the group is very misleading.
The best description of the spacegroup and its equivalent positions is to be found in Niggli's work.17
1aRalph W. G. Wyckoff, The Analytical Dxpression of the Results of the Theoryof Space Groups: Carnegie Institution oJ Washi'ngton, Publication tr[o' 318, secoud
edition, 1930.
16Hermann Mark, Hanilbuch der angettand'ten physi'holi.schenChernie; Bd' 14'
Die Verwendung der R<intgenstrahlen in Chemie u. Technik: Leipzig, 1926, pp'46(H6t.
16Ernst Schiebold, Uber eine neue Iferleitung und Nomenklatur der 230 kristallographischen Raumgruppen: Abhanil!,ungen iler mathematisch-physi'schenKlosse iler
Siichsischen Akailemie il,er WissenschaJten,Yol.40, No. 5, 1929, p. 88'
17Paul Niggli, Geometrische Kristallographie des Discontinuums, Lei'pzi'g,1919,
pp. 198-199.

376

THE AMEKICAN MINERALOGIST

PossrsrB AnnalrcBuBNTS FoR Mnncesrrn'. Since there are two
formula weights of FeSzper unit cell, two iron atoms and four sulfur atoms must be associatedwith each cell. Space group 7a12has
only 2-fold, 4-fold, and 8-fold positions available, therefore theiron and sulfur must be distributed as follows:
Irons in one of the four 2-fold positions, @,b, c, or d,
I by t*or in the remaining 2-fold positions,o,b,c,ord,
I
Sulfurs either: i
I or by fours, in one of the three 4-fold positions,e,f,org.
I
The total possible marcasite arrangements are therefore thoseshown in Table IV. Not all of thesestructures are different however.
By changing the origin of coordinates of each of the sets of coordinate positions by r in the three axial directions, it becomesevident
that a number of these combinations are identical, leaving only thefollowing independent :OneparameterTwoparameter

13

oe

t4
15
16

rJ
be
bl

2l
22
23
24

ag
bg
cg
dg

Finally, by allowing the variable s 0o,06, and 0. to assumeall values
between 0 and 2tr, it can be shown that all possible marcasite
structural possibilitiescan be representedby:
TwoparameterThis makes a total of no more than six possiblestructures.

JOARNAL MINERALOGICALSOCIETY OF AMEKICA

377

Terrn IV. Mexncuu Nmmrn or Possram Mance,srrr Srnucrunrs
INotcarEo sv SpacE Gx.oup
Combination
numberIron
positionsSulfurpositions
bc
bd
cil

1

a

a

a

J

a

4
5
6
7
8
9
10
l1
t2

D

ac

b

oil'
cd
ab
dd
bd
ab
ac
bc

IJ

a

e

t4

a

T

l.)

b

t6

o

o

a

d
a

J

tt

18
t9
20
2l
22
23
24

12 symmetry-fixedstructures.
Sulfurs on s)ammetrycenters

8 one-parameter structures,
Sulfures on 2-fold rotation axes

J
d
d
a

J
6

b

c
c

4 two-parameterstructures
Sulfurs on reflectionplanesd24possible
structures
INrBnsrrv CoNsrrnnerroNs
PuasB FuNcrrox oF Vnrz.The amplitude of a wave scattered bya set of atoms in a unit cell, as a function of the positions of theatoms, may be represented by
p :l*e2 ; ; (h,h * k,0zI l, 0s)
where, I, indicates a summation over the n atonrsconsideredin the cella is the baseof natural losarithms..i:\/i

378

TH E AM ERICAN MIN ERALOGIST

09 02,0xarethephasecoordinatesof an atomh', k', and.l'are the indexnumbersof ttreplanereflecting.
If the crystal consideredhas a center of symmetry, the phase function may be more conveniently put into the following form bysumming over half the total number of atoms, taking the coordinates in centrosymmetrical pairs:
P :1,12 2 cos (h'fu *k'02 *l'li.
The particular form of the phase function for Vnr2is then obtainedby substituting the coordinatesof general positions I,2,6, and 7(each one with its centrosymmetrical derivative understood) inthis relation, which gives:
P : 2 I cos (h'0tl h' 0zll' 0) I cos(- h' 0t- h | 02+I' Os)! cos(h' lr - 0tl-l k' lr I 0zW I' lr - 0 el){ cos(h' [r - 0r]l k' lr I 0zl1-l.'b * 0r))l,using spacegroup orientation. This may be reduced to:falr : l + Icos(h.0")'cos(h0) 'cos(1,0"),whereh*k*tr is evennlzJand(ho").sin(ft').sin(ra"),
cos
where &*fr*l,:is odd,f,iltransformed to marcasite.""rar"u,"r.{X} indicates that coefficientlz)

8, 4, or 2 should be used corresponding to the number of atoms in
the equivalent position considered.
RBlrccrrom fxrnNslrrns. The actual amplitude contribution of
a set of atoms to the reflection of a plane is given bys: F.P
where P is the amplitude given previously and 1r is the scattering
ability of the atom as a function of the angle between the incident
and reflected beam. The P values used for the calculations involved
in determining the structure of marcasite are given in Fig. 5. The

JOURNAL MINERALOGICALSOCIETY OF AMERICA

379

curve for iron has been drawn directly from the data of Bragg
and WestJ8 The sulfur curve has been calculated by the method
indicated by these authors.le The sulfur curve probably does not

F

v

.7oo
.60o
.1oo
.5oo
sii. aFro.5.TheF valuesof iron (uppercurve)and sulfur(lowercurve)usedin the
detbrminationof the structureof marcasite.
.roo

zoo

fall off as rapidly as it should, but for the relatively small values of
sin 0 employed in most of the calculations, it has given very satisfactory service.
The amplitude contribution of all the atom speciesto the plane,or the structure factor, isp : F i,on.p i,oo{2F. psulrur
S :fs :!f'"u1rur
18W. LawrenceBraggandJ. West,A Techaiquefor the X-ray Examinationof
p. 139.
CrystalStnrctureswith manyParameters:
Zeit.fih Krist.r 69, 1928-1929,
LsOp.cit.,p. t37.

380

TH E AMERICANMI NERALOGIST

summed over all the atorn species,in this caseover iron and sulfur.
The intensity of the reflection of a plane is'given by20,-

r - . l t c o s z 2 o:.
s" , 1 . o . s ,

K2

sin20

K2'

where K is a constant for a given apparatus and crystal specimen.
Er,rurNarroN ol fltpossrsl,E MARcASrrs Srnucrunps
INrBNsrrv Colrpanrsows. The iron atoms of marcasite occupy
symmetry-fixed positions, and the sulfur atoms occupy positions of
no more than two undetermined parameters. It is possible, therefore, to calculate the intensities of reflections of various orders
to be expectedfrom one pinacoid for the two parameter strqctures,for two pinacoids for the one parameter structures, and for all
three pinacoids from the symmetry-fixed structures. Comparison
with the intensities actually observed then allows structures to beeliminated which do not give sequencesof intensities indenticalwith those observed. The observed orders of intensities for thepinacoids are as follows:
2A0
strongmediumweakr-"0#,-'J:? "f,'"1,t-:J',X-t'ffJ","""K

In Table II, the intensities (in the convenient torm I,fVIl),ealculated for the different possible arrangements, are comparedwith those observed. Only the two parameter structures,

l'l

I rl
2l-24: l]l .g""tt,., give intensity orders not in conflict witfr thosel0llali.o"actually observed. Since aII these structures are identical, t[ey may
be representedby the singlestructure @iron'gsuuur.
80W. LawrenceBraggandJ. West,op.cit,,p. 125.

JOURNALIIIINERALOGICALSOCIETYOF AMERICA

381

From the above considerations it
TsB MlncesrrE STRUCTuRE.
is evident that the iron atoms occupy symmetry centers while thesulfurs lie in reflection planes. The structure can be representedby
the following coordinates:
Irons at [[000]l and lbrzrrll
Sulfurs at [[0d6d.]1,[ltr,zr 067r! 0)], f[tr7r* 0a7r 0"]i'[[0db0"]1,
It remains now to determine the values of the parameters 0a and0".
DnrnnurNerroN oE Panaunrnns
The two parameters,0oand 0"have been fixed by independently
finding a value of each, for which all planes not involving the othervariable give calculated intensities in the same order as the observed intensities. All intensity comparisons' except as specificallyT.lnln V. OssntvEoPrnacoo lNrrNsrrv Onarns Couperru wns
ConnrsportorrcIxmNsrtm'sCercur-lrnoron Possrsr,E
Mer.cesrrpSrnucturrs
CalculatedIntensities lKy'I I
Plane

200
400

Arrangements

Arrangements

r-tz

13-20

t39
56

Variablewith

Arrangements
2L-24

Observed
Intensities

139

Strong

56

Medium

28

Weak

0n

600

28

020

186

Absent

186

040

83

83

060

45

45

002

225

225

004

107

lo7

006

61

61

Variablewith0t

MediumWeak
StrongVariablewith
0"

AbsentMediumTE E AMERICANMI NERALOGIST

noted beyond, were made on a single c axis, complete rotalion
photograph using a cylindrical camera (Fig. 6). This allows all
intensities to be compared with one another.
In a preliminary way, it is evident from the intensity order:110
verystrongmediumweakabsentFrc.6.Print of marcasite
c axisrotationphotograph.
Thefoggingisdueto r-rays
scatteredbackwardby thepapercoveringof the fiIm dutinga verylongexposure.
that 0amust lie in the general region near 70o,or in its centrosymmetrical region near 290". The centrosymmetrical region may be
temporarily neglected, since it simply indicates the position of thecentrosymmetricalatom.
The variable dais more closely fixed as indicated in Fig. 7, where
the intensities of all planes not involving the other parameter,0",
are plotted as functions of the variable da.At the bottom of the fig_ure, some of the intensity relations which tend to limit the value ofthe parameter are indicated. dais thus fixed at about 73oor 74o car_
respondingto u6:.203 or .205, to within less than a percent of the

JOURNAL MINERALOGICAL SOCIETV OF AMERICA

383't
total possible variation. It is interesting to note that thrs uln" i,almost a6: $ within the limits of accuracy of fixing 06.
As an indication of the correctness of the value of 0u, the intensities calculated (graphically) at0o:73" are listed in TableVI
in comparison with the order of intensities observed on the c axis
rotation photograph. The check is very satisfactory.
An additional check is had by studying the list of planes indexed(Table I). By examining the columns corresponding to the pyramids(h|l),a type permitted by the space group for all values of
it is evident that only such
h,h,l, h+k, h+1, k+1, and hlkll',
planes reflect as have h+h+|, even. Out of at least ten chancesfor
raslevr'core'q'nrsoNT":1#;T"":J|,"^*::1::'ono'nsorrnrexstrros

lrVt I Plane

Observedorder

272

110

110

Very Strong

r39

200

2ffi

Strong

I IJ

150

150

Strong998580V
310,240,350,0410,
400

Medium550

550

Moderately

leol
640l

V

J/

56
52
34
32
31
29
28
,,4

10

460'l
710i
6001

o60J
13ol

o

190,640, 4ffi , 710,600, 060

Weak

V

A

3
2
2
0
0

130,330,020,530,220,420,620,170Absent

17o)

Weak

381

TII E A M ERICA N MI N ERALOGISTKVl'l'lieItrc. 7.
variations of intcnsity Ior all resolved planes within the dimensionsof the apparatus for the r axis rotation and not involving 9", plottedlas functions of
the parameter da. The notation2XhhO indicates that there are lzuapairs of planesin the form reflecting to the same spot on the photograph.

385

TOURNAL MINERALOGICAT. SOCIET'Y OF AMERICA

--v

tI
K",JI

lso

tio

A+
-

3os> oo4
qo2)

600 > lol
3os ) rol --3OS) 6@_=
4OZ)

zatoS >oozF-

to3 i2o2006202 ) lol

l
_

___l

F-lot

) 4o4

r-tol

) 2o4

^

F_-oo6)Oo4

H

F-6oo>4o2

\/r-

l7o

160

l_

2OO> 2*lOS

rO | ----------------i
F_-=---@6)

tol

Frc. 8. The variations of intensity for all resolvedplanes within the dimensionsof the apparatus for the 6 axis rotation, and not involving 0a, plotted as functionsof the parameter 0". The broken cuwes are additional intensity variations plotted forcomparisons of the reflections of certain planes not appearing on tle , axis rotation,
but present on the o axis rotation. The notation 2Xh0l irldtcates there are two pairsof planes in the form reflecting to the same spot on the photograph'

s86

TH E AMERICANMIN ERAI,OGIST

planes with h*h*l
odd to reflect, not one reflection is recordecl.
'fhereis no contribution by iron atoms to the reflections for whichh+k+l is odd, all diffracted radiation being due to the sulfur atoms.
For marcasite, the phase function, p, for the sulfur atoms, takes
the form:p:-Asin(&oo).sin(/d,).
For planes (h5l), this is more specifically:p : _ 4 sin(S0a). sin(ld,).
Evidently the right hand member vaniShes for any value of sin(50a) which is zero. This occurs when 500is 0o, 180o,360o, etc., orwhen 06is 0o, 36o, 72",108", etc. The 72osolution correspondswith
the 0a determined graphically. Any value of 96 very iear to 72owould give rise to a sulfur contribution corresponding to an intensity too small to be detected on the photograph.
The parameter, 0., has been determined graphically (Fig. g) in amanner similar to that used in the determination of 06.rn addition,
Fig. 8 shows the variation of certain planes (dotted curves) not appearing on the c axis rotation photograph, ancl whose observed in-order are given in Table VII. The correspondenceis very good,taking into consideration the following point: reflections lrom
planes located near the center of the rotation photograph, and onhigh layer lines always appear too intense, compared with calculated intensities. This is a normal condition, caused,in part, by thegreater thickness of the splinter shaped crystal traversed by thesebeams. rn no casehas this effect seriously impaired the closenessof
parameter determination.

IOURNAL MINERALOGICALSOCIETY OF AMERICA

387

Teslr VII. CoupanrsoN or Celcularno lxo OesBnvop Onnrns or INtpr'Isrrres
rcn (h0l) Pre.NEs,Ar 0c- 1350

lrvil

Plane

Obsewed order

103

Very Strong

200

Strong400, 303, 202,305

Mediumffi,402

Weak

t39
't07

200
103

s6
s6
s2
38
28
24

4ool
303f
202)
305]|
600|
4o2)

16
7

101
204)

101

s

3o1l

204,3Ot,n4

3

4O4)

Very Wea!
Absentof plane, the total diffracted radiation is due to the sulfur atoms.
In this case, the phase function takes the form
P : - 4 s i n ( f r d a ) . s i n( 4 0 " ) .
The right hand member vanishes for values of 4d, equal to 0", 180o,
360o,etc., or for values of d" equal to 0", 45o, 90o, 135", 180o,etc'
The 135osolution is identical with the value of the parameter already determined.
As frnal checks on the proposed parameters, Table VIII shows
the graphically calculated and the observed intensities of planes
not involving d", and planes not involving 06,both taken together
for comparison, and Table IX shows the calculated intensities ofaII planes having values of sin d less than .4, and not near the central portion of the photograph. To include planes of higher valuesof sin 0 would be to push the proof of accuracy of the parameters
beyond the ord.er of accuracy of their determination. The checks
are blearly satisfactory.
TsB MancnsrrE SrRUcruRE
The
DBscnrprroN.
considerations just detailed lead to a comof
thestructure of marcasite, in the following
plete description
terms:

388

TH E AMERICAN

M IN ERALOGISTUnit cell: a:337 A
b-4.44A
c : 5 . 3 9A
Spacegroup: 2612
Tesrn VIII. Cow.rnrsoN o*'Carcuurno.lwo OssrnvEn Ononns or Iw:rnxsrrrus
non (hkO) eNo(hAl Plawrs, ar
0o:73"
0":130o
Plane

Observed order

110

ll0, 103

t39

200

200

Strong

I r.)

150
103

150

StrongMedium

107
99
6J

80

31ol
2nl
3s0l
040|

4ool

310,24n,350,040,400,303,202,305

56
.)o

303I
202)
s50

V

J/

52
52
38
34
32
3T
29
28
26
24
16
10
7
6
4
3
3

0
0

Very Strong

550

:n <)

JvJ

I

V
190,640,4@,710,600,060,402

402)
101

weak

V
101

Very WeakV
130,204,330,
301,020,404,530,
220,420,620,17O

AbsentJOURNAL MINERALAGICALSOCIETY OF AMERICA

389

Iron atoms(on symmetrycenters)at: [[000]land [[]*]ll
Sulfur atoms (on reflection planes)at : flDu6v"ll, llD'iltE"ll,-v
lE,l - ut,ttu"ll, andll+,++ ub,+"ll
ut:'2031'ol*n"r. I tz" :.3 7+5 .0 1\

corresporrdinc,";:r=::=lIi{
Tesln IX. CoupantsoN ol Cercur,ernp llro Ossnnlto Ononns ol lNrerqsrrrEs roR l.rr- Pr,eNrs Hel'rNo srn 0 Urvnrn .4 aNn Posrrroxs Nor Too NEAR
CnNrrn ol Puoroonarn, lt[oo:7t'i.o,:135"

lrvil
272
226
151
147
t39
113
109
r02
99
89

Ptane

Observed order

110
t2l

rl0, l2l

23r+04r
unresolved
111
200
212
s2l
'l 77 -L77)

unresolied
310'
r3t+221V(231+041),
lll,200

Very Strong
Sfrnnounresolved

V
212,321,(132+222),03I

SfrnnrunresolvedV

unresolved

86
85
83
60
J/

37
35
t6
10
8
A

031
2N
2rl
311
040
021
n?t

101
130
t4l
301
020
220

310,(l3l+221), 24O,2ll, 040,311
unresolved

MediumVo21,032
101

Weak
Very WeakV
130,141,301,02o,220 Absent

390

TE E AM EMCAN MI N EMLOGISTfor the marcasite studied. The coordinates are referred to the conventional marcasite orientation, taking the origin at a symmetry
center.

I

L
j

f

zc

Frc. 9. (001)-plan(upperleft), (lO0)-elevation(Iowerleft), and (010)-elevation(lowerright) of marcasite.
Theiron atoms(stippled)andsulfuratomsaredrawnto
scale.The relationbetweenttre sulfur pair and iron triad is well seenin ttre lower
dght (010)elevation.The bottomthreeironsform the triad, to whichis attached,belowandin back,thebottomtwo sulfurs.The axisof the sulfurpairslopesdown
andbackawayfrom theiron triad.
A unit cell of this structure, together with a few additional atoms
to complete the picture, is shown in Fig. 9. The structure is identical with the one proposed by Huggins on grounds of atomic theory
and shown in Fig. 2. From a certain point of view, it can be easily
visualized as a stack of separate(100) planes; each plane consistsof
parallel strings of Fe-S, S-Fe-S-S- - - extending in the directionof the c axis with all the iron atoms in a straight line, but with thesulfur atom pairs nesting zigzag between these irons and causing
the crooked appearanceof the string. Adjacent threads have sulfur
pairs pointing in the same direction, but adjacent planes havethem pointing in reversed directions. Between (100) planes the fit

JOT]RNALMINERALOGICAL SOCIETV OF AMEMCA

39L

is made by contacting an iron atom of one plane with the nearest
sulfur atoms of neighboring strings in the next plane.
GBounrnrcar- PRoPERrrEs.Various important geometrical properties of the structure of marcasite can be calculated as follows:
Pairedsulfurdistance:

AB: \/@FTG -83:2.2s4.
Unpaired sulfur distances:

AE : \/Q=zffi//o\2+ Q - 2%Y: 2.s64
/b\2

,\2

/,

AC: ( (;)+(;,)+\r'"-T):3.104

.

/b
\2
/c\2
a\2
oo : t// /(t/+ \z - 2*)+ (;/ : 3 16,{

A A ' ( t w o ( 1 0 0 ) s h e e t sa P a r t ) :fron-iron

a:

3374'

a :

3.374

distances:
DD' (two (100) sheets aPart) :/ / a \z+ /1 \io':l/\z/\2/
O O z- c :1 a \,: e .ssa
\2/

5.394

DDl : \/F+W:

5.524

Iron-sulfur distances:

Ao: \/ip:r77:2.214^o-tto:,27 b\24/(;)+\t-,,)+\z-,)/c\2:2214'The structure displays 6-3 coordination. The iron atom, D issurrounded by six sulfurs at distances which are identical, within
the accuracy of measurement: two sulfurs in the same plane, C andG, centrosymmetrical with respect to the iron; two in the plane infront, .4. and.E; and two in the plane behind, centrosymmetricalwith / and.E. All these surround the iron at a distanceof'2'2I2.24 A. The sulfur atom, A, in turn, has three irons nearest it at
this distance O, in the same plane, and D and D' in the plane infront and behind.

TH E T|MERICAN MIN ERALOGIST

ll'he relation of the structure to other sLructures can best be
visuallized by separating a sulfur pair with its immediate ironenvironment. This group, as indicated in Fig. 18, is a sulfur pair
capped at each end by an iron triad. The triangles formed by theiron triads are rotated 180' with respect to one another. These
triangles are not exactly equilateral, but are rather isosceles,as ind i c a t e db y t h e d i s t a n c e s ;D D ' : 3 3 7 A ; O D a n d ,O D , : 3 . 8 8 A ; t h eacute angle is about .51foinstead of the ideal 60o. The angle which
the plane of the iron triad makes with the d.irection of the sulfur
pair is very closeto the ideal 90o. For the parameters given, it canbe calculatedas:
18oo_ tan_t(b/c)_ tan_,/;t_\:

970\z-"I

Ror-arrox ro OrHER SrnucrunBs
PvnrrB. These same units in the undistorted, ideally symmetrical condition are distinguishable in pyrite, and indeed it was on theassumption that these units carried over from pyrite to marcasitethat Huggins2l proposed a structure for marcasite. The difierence
between pyrite and marcasite is essentially one of a difierent linking of these units, at the same time satisfying the 6-3 coordination
requirement.
Table X certain geometrical properties of pyrites2are given in,Incomparison with those of the marcasite structure, to bring out theessentialidentity of this common unit.
RurrrB. The rutile structure is a special case of the marcasite
structure. The marcasite structure tends toward the rutile structure by decreaseof the distance between the sulfur atom and theplane of the iron triad. When the sulfur atom actually occupiesthe
plane of the iron triad, and the triad makes an angle of 90" with thesulfur pair, it is identical with the rutile structure type.
Proof of the close relation between the marcasite ancl rutile
groups, as well as an excellent visual check on the general correctnessof the marcasitestructure, is offeredin Fig. 10,in which stand2r Loc. cit.
22Pyrite designations anddistances taken from: p. p. Ewatd and C. Hermann.
structurbericht, 1913-1926, p. 153 (supplement to recent numbers of.zei.t. Kri.st.).

JOURNAL MINERALOGICALSOCIETY OF AMEruCA,393

ard crystal drawings of marcasite,2sltillingite,24 and rutiles are
given in the same orientation for comparison. The tetragonaloid
aspect of the marcasite group is obvious.
Tl,sLEX. Courenrsor or CnnrmNDrmmsroNsol rrm Comror UNtt ol' tgn
Pvrrrr ervoMlnc.lsrtr S:rnuctunns
PyriteJoplinmarcasite

Paired sulfur distancesd.:2.t04

AB :2.254

fron-iron distancesin triad\I:s.82

Ir:s.zz
17:s.sz

DD':3.37.
OD:3.88
OD':3.88

le:2.26

ao:2.2r

Distancesfrom sulfur to irons
in nearesttriad\ e:2.26

le:z.26

AD:2.24AD'-2.24

Distance from apex of oneiron triad to centrosymmetrical apex

lo:s.nla:s.40
lo:s.a0:5.39
c
DDz:5.52
DDz:5.52

Angle betweensulfur pair
and iron triad

90'

TUB

CUBUTCAL NATURE

I

Q70

OF MARCASITE

Rnorr ol Sur,run ANDIRoN Arorus. The geometrical properties
listed indicate that the closestiron-sulfur approach is identical withthe closestsulfur-sulfur approach, to within the limits of error of thedetermination. Slight changesin the parameters do not destroy the
essential nature of this feature. Assuming that both the iron andsulfur atoms behave like rather hard spheres,it follows that they
have the same radius, namely; about 1.12A.
B Traced from: Victor Goldschmidt, Atl,as iler Kri'stoil'l'formen,Heidelbetg,l92O,
vol. 6.
24L. H. Bauer and H. Berman, Lollingite from Franklin, New Jersey, ,424.
Mineral., t2, 1927, p. 4A.
25Habit taken from Dana's System, (1914), p. 238, Fig. 4, but redrawn so thatthe rutile c axis direction corresponds with the marcasite and ldllingite o axis direction, and the mtile at and aa axial directions corresponding with the marcasite andldllingite

D and c axial directions.

394

TH E AM ERICAN MIN ERALOGI ST

RutrleMarcasite

La//inqife

Frc. 10. Comparison of the habits of the rutile and marcasite groups. As redrawn,
the rutile c axis is parallel with the marcasite and ldllingite o axis direction. otheraxes are parallel. Corresponding faces, referred to this orientation, have identicalindices.

SrarB ol foNrzarroN. The proba.ble state of ionization of theatoms in marcasite may be investigated without any chemical assumptions whatever by considering the sulfur-iron spacing to be expected from sulfur atoms and iron atoms in various states of ionization. The situation may be appreciated at a glance, thus:26
26Radii from: V. M. Goldsmidt, Geochemische
Verteilungsgesetze der Elemente,
vol. 7: ShriJter utgitt ar Det Norske Vid.enskaps-Ahad.emii. Oslo I. Matem.-Nah.atid.
Kl.asse, 1926, No. 2, pp. 26, 34, and 43.

JOURNA,L MINERALOGICTL SOCIETY OF AMERICA

395

rite, where this distance is 2.26 A.
AcrNowr.noGEMENT

also facilitated. my work during the density determination'
I wish to thank riry colleague,Prof . B. E. Warren, for permission
to use the rotating crystal apparatus of the Department of Physics
of the MassachusettsInstitute of Technology, pending installationof suitable equipment in the Mineralogical Laboratories' Dr' Warren has also been kind enough to aid me at a number of points during my first working contact with the rotating crystal method'
This is the first of a seriesof papers dealing with the crystal structures of the marcasite group. The others, it is expected, will appear
shortly.