CONTRIBUTIONS TO THE MINERALOGY OF STERLINGHILL, NEW JERSEY: MORPHOLOGY OF GRAPHITE,ARSENOPYRITE. PYRITE. AND ARSENIC
Cnnnres PAr-Acue,
H ar var d, (Jnitsersit y, C ambr i d.ge, M ossachuselts-*
GnepurrB
No satisfactory data for the morphological determination of the symmetry and elements of graphite have hitherto been published. Goldschmidt (1913), unable to decide between Kenngott's hexagonalinterpretation of his meager data and the monoclinic interpretation of Nordenskjtild, gives both in the Atlas.The former has, however, been accepted by most authors and the mineral has been described as hexagonal-rhombohedral, the triangular striations commonly to be seen on
the base determining its rhombohedrai classification. Recent studiesof the structure cell by tc-raymethods lead to the conclusionthat graphite
is hexagonal (Bragg, 1937) and not rhombohedral, although a trigonal
symmetry classis not excluded.
The measurementspresented in the following pages' made on graphite
crystals from Sterling Hill, New Jersey, seem to the writer to yield adefinite and unambiguous solution of this problem. Graphite is hexagonalwith full symmetry.
The graphite crystals from Sterling Hill occur in crystalline limestone in an association to be described on a Iater page. I am indebted
for them to Mr. L. H. Bauer of Franklin, New Jersey, who found thematerial and isolated the best crystals. They are scalesup to 1 or 2 rrrm'
in diameter, the best ones, however, not exceeding0.5 mm. The base isextremely brilliant, hexagonal in outline, with edges showing many
facets, often very plane and bright, although striated edgesare the rule.
Of the hundreds of crystals studied, ten were completely measured andyielded the forms and angles shown in Table 1. Four of these crystals
were very simple in form and gave closely agreeing measurements forthree forms only besidesthe basal pinacoid, which are regarded as definitely proving the hexagonal symmetry of graphite. They are summarized in Table 2.
But one of these crystals showed measurable faces at the lower end,
and it was unfortunately lost in attempting to reverse it on the goniometer. Figures 1,2 and.3 representrespectivelycrystals 1, 3 and 4 of
Table 2 in approximately their actual development.
* Contribution from the Department of Mineralogy and Petrography, Harvard Universitv. No. 248.

709

7r0

CHARLES PALACHE
Tanr,n 1, Greprrrtr: Musunro

ANcr,rs. 10 Cwsrnrs

Calculated
p

,n
d
e

10T0
1018
10f5

30'14' 90000'
30 53 20 49+
30 31 32 03

0"00,_|"22,
90'00'o 1 6 - 1 2 9 20"49',-20"50', 21 l0
0 0 0 - 1 3 2 30 38-33 14
32 26+

107
2l
43

t
r
o

lo14
tOI3
lO12

30 t2 38 24
30 29 46 59
30 13 57 48

0 1 0 - 01 4 37 48-39 00
0 0 2 - 0 4 0 45 49 -48 30
0 0 4 4 2 2 57 10-58 30

s8 28
46 39
57 49

22
84
t26

w

2023
4045
10T1

30 26 64 43
30 16 69 07
30 00 72 32

0 0 4 - 1 2 4 63 40 -65 45
0 0 0 - 0 4 0 68 23 -69 46
0 0 0 - 0 0 5 72 2l -72 50

64 M
68 31+
7232

43
43
184

2021
1126
1123

30 20 81 10
0 38 42 35
0 59 61 28

0 1 5 - 0 2 5 80 20*82 00
0 0 7 - 1 1 0 42 1542 55
o 0 7 - 2 0 9 59 00 -64 30

81 03+
42 32
61 24+

22
2l

1122
2243
rr21

0 09 70 02
1 05 7440
0 30 79 52

0 0 3 - 1 3 3 69 15-70 40
0 0 0 - 3 1 6 7s 47-7s 40

7002
744s+
7952

61
44
11

p

v
o

a
T

Teern 2. MresunnunNrs

Crystal 1
p 101rCrystal2

p r0rro 1012Crystal 3
p t0rlo 1012Crystal 4
p 101ro ll22oF 4 CRysrArs oF GRAprrrrE

6 faces+2+'
29"57+',+p+ 5'
72o27'

5 faces
3 faces

2 95 r + 1 4
2 95 0 + 1 2

7237+95 7 1 8+ 1 8

4 faces
6 faces

2 95 0 + 1 3
2 95 0 + 1 3

7 23 9 + 2 r
57 42++12

6 faces
6 faces2955 + 7
0 40 +51

7 23 2 + 2 07002 +38

The other measured crystals were more complex. Figure 4 illustrates
one of them and it is evident that individual forms are irregularly developed, no one pyramid having all its six faces present. But the distribution in this and in every crystal is not systematically trigonal but
random. It is also true that other reflections were obtained from somecrystals which were not in the dominant zones and which could not be

CONTRIBATIONS TO MINERAINGYOF STERLING HILL, N. J.

simply indexed in the projection. But these were always subordinate to
the prevailing hexagonal distribution.
From the mean values for the position angles shown in Table 1 theelements were calculated, using 69 faces of 11 forms on 10 crystals. The
resulting value, ps:3.1780, c:2.7522, is taken for the calculationof theangle table, Table 3.
TLsrn 3. Gnepsrrn: Altcr,n T.q.sre
Hexagonal, Dihexagonal-dipyramidal 6/ m 2/ m 2/ na : c : 1 : 2 . 7 5 2 2; p o :r n : 3 . 1 78 O :1.
Az

Forms
0000'
90 00
2t 10

90'00'
60 00
79 36

90"00'
90 00
90 00

3226+

r 101-3

30 00
30 00
30 00

7+ 26+
7l 54
68 41

90 00
90 00
90 00

o lO12w 2O23x 4O45

30 00
30 00
30 00

57 49
6444

64 58
63 07
62 16

90 00
90 00
90 00

2 1011y 2021
r 1126

30 00
30 00
000

8103+
42 32

61 31
60 24
90 00

90 00
90 00
70 14+

p tt2361 24+
70 02
74 4s+

90 00
90 00
90 00

63 37+
61 58
610e+

79 42

90 00

60 32

r 0001m 1610d 1018e 1015t ro1430000'
30 00

o

zz+J

000
000
000

r

ll2l

000

6 rr22

38 28
46 39

6831+
1.1 JLThe elements calculated from r-ray measurements are po:3.170,
c:2.745. The commonly acceptedelementsof graphite based on Kenngott's (1854) original measurementsare, if c be doubled, ps:3.2006,
c:2.7718, but regardingthis value seethe remarks on a later page.
Confirmation of the results obtained from these measurements wasfound on a single crystal of graphite from Ticonderoga, New York, shownin Fig. 5. Although of much poorer quality than the Sterling Hill crystals,
it gave mean angles for two forms which are comparable:

p r01ro 1012o
6 faces
2 faces

29"57',
29 54

p

72"s6+',
5739

712

CHARLES PALACHE

.t -l

t:
6

Frc. 1. Plan of gtaphite crystal from Sterling Hill, N J., showing the forms
c[0001]and 2{1011}.
Frc. 2. Plan of graphite crystal from Sterling Hill, N. J., showing the formsc [ 0 0 0 1p] ,[ r 0 T r la n do { 1 0 f 2 } .

Frc. 3. Plan of graphite crystal from Sterling Hill, N. J., showing the formsc [ 0 0 0 1] , r ' [ 1 0 1 1] , a n d .6 { 1 1 2 2 \ .
Frc. 4. Plan of graphite crystal from Sterling Hill, N. J., showing irregulardisposition of faces of the forms.
Frc. 5. Graphite crystal from Ticonderoga, N. Y., showing full hexagonal
symmetry with the forms c{0001}, mll010l, otl012l and p[10T1].

CONTRIBT}TIONS TO MINERAI.OGY OF STERLING HILL, N. T.

7I3

Frc. 6. Graphitecrystal from SterlingHill, N. J., showingthe forms c{0001} andp{1011},with a twin lamellaon [1121].A cleavageplanebelow.
Frc. 7. Crystal of arsenopyritefrom Sterling Hill, N. J., showing the formsm{ll0l, q{210}and nlt0ll.
Fro. 8. Crystal of arsenopyritefrom Sterling Hill, N. J., elongatedon b showing
qtzr0l, el0r2l and z [ 101| .
from SterlingHill, N' J., showingb[010], q{210},
Frc. 9. Crystalof arsenopyrite
due to striation.
el0t2\, nll}l\ and a pseudobase
Fro. 10. Crystal of arsenopyritefrom Sterling Hill, N. J., equant, with
ql2l0\, elll2l, and z[1011.
Frc. 11. Crystal of native arsenicfrom Sterling HilI, N. J., showing
and 2[0112]'c{0001},ell}I4l, J12021},

This crystal was the only one on which the faces of the lower end could
also be measured; they were so placed as to indicate a horizontal planeof symmetry.
Forms. The base {0001} is the dominant form on graphite from all
localities. Generally it has splendent luster and is invariably used fororientation of a crystal on the goniometer. [1010], the prism of firstorder, is very weak, rarely present as more than a line face, and often
quite missing, always rough. Dipyramids of the first order determine thehexagonaloutline of the scales.The forms {1011} and 11012}are about
equally common, {1013} slightly less so. The other six dipyramids aresubordinate. No one of the dipyramids is complete in most casesbut
rarely all six faces of some one may be present. The zone of these faces
is often completely striated so that a chain of overlapping signals is allthat can be observed on the goniometer. Dipyramids of the secondordernever determine the outline of the crystal. They appear as tiny facets on
the angles of the hexagonal scales or as line truncations of first order
dipyramids.
Twinning.In selectingcrystals for measurement,those whosebase wasquite free from striae were sought for. The vast majority of the crystals
showed striations on the base in one, two or three directions, always indiagonal relation to the hexagonal outline. Two were measured uponwhich a single twin lamella traversed the crystal with a sharp plane faceof the pinacoid in twin position, making an angle to the base of about
20o, as sh_ownin Fig. 6. This correspondsto a face as twin plane of theform { ll2ll , which requires an inclination of 2A%6'. A corresponding
angle,20o24',was observedby Sjdgren (1SS4)on a twin crystal. Anothermeasuredlamella gave an angle of 16"43', corresponding most nearly tothe form {4483} as twin plane, which requires an inclination of 15o31'.
Kenngott measured a face parallel to the direction of a twin lamella
making an angle of 58o to the base, but it does not appear clearly from

714

CHARLES PALACHE

his description whether this was a face of the main crystal or was upona twin lamella. He took it to be the former and made it his unit rhombohedron, but this angle correspondsto no pyramid in the second orderseries.If, however, it be regarded as a twin lamella, the angle corresponds
to the position of the base when twinned on a face of l1123l, which requires an angle of 57"11'. In short, the twinning of graphite may be defined as on a face of a second order pyramid not well determined but
most probably the form ll12ll. It is evident that twinning on such aform would be possible on six faces of the pyramid which would havetraceson the basein but three directionsat 120oand could give rise to
trigonal or hexagonalstriations. The striae are due to gliding, as has long
been recognized,and may be easily demonstrated by the slightest pressure on an untwinned crystal. Examination under the binocular of aplate deformed by pressurereveals on various parts of the surface every
sort of combination of the six gliding surfaces, single lines or pairs,
isoscelestriangles or hexagons, so that there seems no reason to doubt
the correctnessof this interpretation.
Kenngott stated that all his measurementswere approximate, particularly that of the form parallel to the basal striae which he took as unit
rhombohedron and on which he based his element. The fact that thec-axis so derived is so nearly in accord with that of our position as shown
on a preceding page is due wholly to chance. The following tabulationshows the angles of his three forms compared with the nearest calculated
angles of the two seriesof dipyramids in our position.
Kenngott

Palachepp

R:10T1n0001 58.00,
3P':1123n0001 43 00
2Pr:112t\000t
7000

1012
1126
rl22

57"49'
42 32
7002

1123
1013
1011

61 24+'
46 39
72 32

The agreement of Kenngott's angles with those of our first column isperfect, but the relation of his forms to the striae on the base makes it
impossible to accept this agreement. His values must be compared to our
secondcolumn and there the agreement is very poor. We can only blame
the quality of his crystals.
Kenngott did not figure his crystals of graphite, but in Descloizeaux
we find a figure drawn, as stated, from Kenngott's data. There is nothing
to be found in Kenngott's paper to show that the habit of this figured
crystal is true to nature. But it so happens that the crystal is drawn in theposition adopted in this paper, and the relative proportions of the forms,
especially of the secondorder pyramid, shown with three faces only since
it was regarded as a rhombohedron, is strikingly like our Fig. 4. Thus,

11NTKIBUTIONS TO MINERALOGY OF STERLING HILL, N. J.

715

also by chance,the only figure of a graphite crystal extant is now justified
by new observations.
During the progress of this study, Dr' M. A. Peacock examined the
projections of some of the Sterling Hitl crystals of graphite and afterwards drew up a projection, based on the elements determined by r-ray
stud.y. In this projection he introduced the lattice planes with greatest
spacingswhich were to be regarded as probable crystal forms. The forms
so indicated are the forms of Table 1 bearing the letters c, nc, e, t, r, o,
P, !, p, @,and r. The only form in his projection not found by any observer is the second order prism. Our list has, in addition, five forms
d,,w, Jc,zr,and a which are all weak and infrequently occurring.
The comparison of the completed form list with Dr. Peacock's projection, quite forgotten in the year or more during which the study has
extended, revealed a parallelism so close as to seem worthy of record as
an additional evidence of the correctnessof the present interpretation ofgraphite morphology.
Paragenesi.soJ the Sterling HiIl Graphite
In May 1937 there were found on the 900-foot level of the mine at
Sterling Hill, New Jersey, specimensshowing an entirely new paragenesis
for this locality. Samples were presented at that time to the Harvard
Mineralogical Laboratory by Mr. L. H. Bauer, and repeatedly in the
succeedingyears the same donor has sent selectionsof carefully isolated
crystals of the several minerals. Description of the material has been solong delayed because only recently were really decisive crystals ofgraphite found which finally solved the ptzzle of its morphology.
The specimensconsist of massive, coarsely crystalline limestone, withirregular impregnations of the following minerals: graphite, native arsenic, realgar, pyrite, arsenopyrite, diopside, and a few needlesof either
stibnite or a lead sulphantimonide. Since all of these minerals are set free
without sensibleinjury by solution of the limestone in dilute hydrochloric
acid, an abundance of the crystals of most of them can be obtained withease.Arsenic, realgar and the antimony compound are quite new to theFranklin region.
The chief interest centered in the brilliant scales of graphite whichwere found in considerablenumbers in the solution residue. The scales
range in size from minute specksto plates 2 mm. in diameter and .5 mm'in thickness. The base is extremely brilliant and the edges of the hexagonal plate show many facets. The details of their crystal form havealready been presented.Most of the graphite crystals are distorted, having suffered from movements in the embedding calcite which has caused
the development of numerous gliding-plane twin lamellae in both calcite

716

CHARLES PALACHE

and graphite. Occasionally, however, the graphite has escaped all distortion or at least shows only a single twin lamella. The graphite crystals
are generally quite free but may be partly embedded in arsenopyrite, inarsenic or in diopside.
AnsBNopynrrB
Next in abundance and beauty of the isolated crystals is arsenopyrite.
The crystals, while minute, are of amazing brilliance and perfection ofform. They present few crystal forms but range in habit from needlesof
hair-like finenessto stout prisms or flattened plates. In dimensions they
commonly range from .5 by 1 mm. to I by 2 mm. They are chiefly
b o u n d e db y t h e f o r m s * m { 1 1 0 1 , q l 2 t } l , e l 0 t 2 } , a n d ,n { 1 0 1 }. O f t h e s en
is generally largely developed and the hair-like crystals are elongatedparallel to it. Commonest type has n and q alone, or with zr as in Figs.
7 and 8, the latter an attempt to delineate the hairlike needles. By
flattening parallel to one pair of planes of n the crystals take a platy
form. Another mode of flattening is by development of a striation zone
over the basal edge as in Fig. 9, producing a dull pseudobase;e is also
common and may be equally developed with n and g as in Fig. 10. Sometimes but one face of e is present. There is a strong tendency for striae
to form between e and n which is generally accompanied by a similar
striation between n and q as shown in Fig. 7. This latter is often so deep
as to eliminate the prism planes. Fig. 9 shows a rare type in which1010| truncateswhat is commonly an acute end.
other forms measured on single crystals or in single faces or pairs are{ 610}, {430}, { 111 }, { 113}, {416} and l2t2l. It is hoped that ananalysis
will be made of these exceptional crvstals of arsenopvrite.
PvnrrB
Pyrite, much lessabundant in the residuesthan arsenopyrite, is present
in model-perfect crystals of varied habit. The following combinations
w e r e n o t e d : { 1 0 0 } a n d { 1 1 1 } ; { 1 2 0 } a l o n ea n d w i t h { 1 1 1 } ; a f e w v e r yb r i l l i a n t c r y s t a l ss h o w i n g { 2 1 0 } , { 1 1 1 } , { 1 1 0 } a n d l t t 2 l .
AnsBurc
Arsenic is present in but few grains and crystals. However, one wasfound to be measurable which yielded the forms c{00011, e{tOl+1,
f { 2 0 2 1 } a n d 2 { 0 1 1 2 } a s s h o w ni n F i g . 1 1 .
Realgar is in rude prismatic individuals with ragged terminations
which admit of no measurement.
* Theforms,s;rmbols,
anddrawingsarein the newpositionrequiredby the resultsof
the studyof this mineralby Buerger(1936).

CONTRIBUTIONS TO MINERAINGYOF STERLING HILL. N. J,

7t7

Needles of an antimony compound have been mentioned. Too little
was secured to enable its satisfactory determination.
Diopside is the most abundant of the residue constituents. It forms
irregular clusters of rounded crystals, white in color and identified only
by its optical properties, since the crystals were too ill defined to beinterpreted.
In the writer's genetic classificationof the Franklin minerals (Palache,
1929) a subgroup was set up called "pneumatolytic products" which wasstated to be practically confined to the Franklin deposit. This new paragenesisappears to belong to this group and extends its range to Sterling
HiII.
RnlrnpNcns
Bnrcc, W. L., AtotnicStructoreof Minerals,54 (1937).
BUERGER,M. J., Zeits.Krist.,95,83 (1936).
(1874),Plate 44, fig.263, reproducedin Goldschmidt,,4tlas
Dnscrozrux, 4., Minero.l,ogie
4, Plate 61, fig. 5.
Gornscrnaror,Y., Atlas d,erKrysl,ol$ormen,4, 89 (1918).
KrrNcorr, 4., Acad.Wien,Ber. f3, 469 (1854).
P.arAcrn, C., Am. Mineral., L4, | (1929).
Sycicrs,N,
H., Ak. Slockholm,}Ttt.
+1, #4,29 (1884).