Pyrite

MINERALS INDEX

Pyrite

FeS₂

Isometric-pyritohedral

Forms
a(100), o(111), d(110), e(210), f(310), p(221), c(433), m(411), m(311), n(211), t(421); doubtful: ?(744) and ?(655).

**Combinations on crystals of pyrite**
(Letters marked with an asterisk (*) indicate the dominant forms)
	Forms	Illustrations
1	o	Figure 4.[sic]
2	o and a, equant	Figure 5.[sic]
3	o and a, equant, and e	Krause and Scott (191), Figure 5.
4	o, a, and e, all equant	Figure 6.[sic]
5	o and e, equant
6	o and m	Figures 7 and 8.[sic]
7	o*, a, and n	Krause and Scott (191), Figure 7.
8	o, m, and m
9	o, e, a, n, m	Idem, Figure 8.
10	o, e, a, m, ?(744), ?(655)
11	a
12	a*, o, e	Idem, Figure 13.
13	a* and o*, equant, and m	Figure 9.[sic]
14	a, o, e, c, n, m
15	a and e, equant, and o, n, m, m	Idem, Figure 12.
16	e
17	e*, o, a, m	Figure 10.[sic]
18	e*, o, p, n, t	Figure 11.[sic]
19	m, a, o	Krause and Scott (191), Figure 9.
20	m*, m, o, e, a	Idem, Figure 10.
21	t, a, d*, f, e	Idem, Figure 11.

Composition
The composition of the mineral, as shown by the analysis, is normal except for the presence of cobalt in about the same proportion is in arsenopyrite from the same locality. (See page 34.)

**Average of two analyses of pyrite**
(Kraus and Scott (191), analysts)
S	53.30
Fe	45.20
Co	1.25
Ca	trace
SiO₂ (residue)	0.03
	99.78

Occurrence
Franklin: The most interesting occurrence of pyrite is in the Franklin limestone, notably in the Fowler and Furnace quarries and in that of the Franklin Iron Company. It is found in isolated crystals of brilliant luster and perfect symmetry developed on all sides, ranging from microscopic dimensions to more than 1-½ inches in diameter. (See plate 2, B.)

Figure 6 Crystal of pyrite showing the octahedron alone. Fowler quarry, Franklin.
	Figure 7 Crystals of pyrite showing the octahedron and the cube in balance. Fowler quarry.
Figure 8 Crystal of pyrite showing the octahedron, the cube, and the pyritohedron equally developed. Fowler quarry.

The habit of the crystals is extremely varied, as shown by the table of combinations. Even in crystals from the same hand specimen different forms are dominant. The octahedron, cube, and pyritohedron are the principal forms, and each occurs both alone and in combination with each or both of the others in balanced development and with all intermediate degrees. Combinations of the octahedron and the trapezohedrons, the latter forms being dominant in some crystals, are peculiarly striking, the trapezohedrons being generally striated parallel to the intersection with the octahedron, owing to the development of two forms of oscillatory combinations. In the paper by Kraus and Scott (191), in which these crystals are figured, nine types are recognized. It seems to the author, however, that the habits are endlessly varied and that the types recognized are limited only by the number of crystals examined.

Figure 9 Crystal of pyrite, showing the octahedron modified by unequally developed faces of a trapezohedron. Fowler quarry.
	Figure 10 Crystal of pyrite, showing the octahedron and trapezohedron in balanced combination, with striae. Fowler quarry.
Figure 11 Crystal of pyrite, showing the octahedron, the cube, and the pyritohedron modified by small faces of a trapezohedron.

The smaller crystals are readily removed from the limestone matrix, but the larger ones are liable to break and have to be freed by careful tool work, an art much practiced by the mineral collectors of the vicinity. Series of carefully worked out crystals of pyrite are among the most valued ornaments of the local mineral collections. Large crystals are now found rarely but seem formerly to have been abundant. They are associated, as a rule intimately, with tourmaline, phlogopite, edenite, graphite, arsenopyrite, and pyrrhotite.

Pyrite is unknown in the zinc ores themselves but is not uncommon in secondary veins traversing them. Thus it was noticed in transverse veins at and near the Trotter mine, at the Parker shaft, and in the Buckwheat mine, everywhere associated with and subordinate in amount to sphalerite. In porous dolomite in the Buckwheat mine were minute crystals of extreme brilliancy, most of them simple pyritohedrons, but a few showing the interesting combination no. 18, a coign of which is shown in Figure 12. The other occurrences noted above were in massive form or rough cubic crystals.

Figure 12 One coign of a crystal of pyrite showing the pyritohedron modified by faces of the octahedron, a trisoctahedron, and two trapezohedrons. Buckwheat mine.
	Figure 13 Crystal of pyrite, showing the octahedron and the cube modified by a trapezohedron. Fowler quarry.

Sterling Hill: Although pyrite is listed by Kemp (152) from Sterling Hill, its occurrence there could not be established either by record or by authentic specimens.


	Website © by Herb Yeates 1997-2001.
	This page created: January 12, 2001 6:47 PM