394 
DESCRIPTIVE MINERALOGY. 
Putnam County. I also refer to this species the crystals which are sometimes met with in 
the magnesian limestone of Hustis’ farm in Phillipstown. These crystals are sometimes half 
an inch in length by an eighth of an inch in diameter, and have the form of right rhombic 
prisms. They are of a pale yellow colour, and are usually very easily decomposed, being 
converted into a red oxide of iron, still retaining the crystalline form of the original mineral. 
It is quite probable that many varieties now referred to common iron pyrites, will hereafter 
be found to belong to this species. In the absence of crystalline forms, it is almost impos¬ 
sible to decide. 
The massive and fibrous varieties of white iron pyrites are found abundantly in various 
parts of Massachusetts and Connecticut. 
ARSENICAL IRON PYRITES. 
Fer Arsenical. Hauy. — Arsenical Iron. Cleaveland and Phillips. — Arsenical Pyrites. Thomson — Mispickel. 
Beudant and Shepard. — Prismatic Arsenic Pyrites. Jameson. — Prismatischer Arsenic Kies. Mohs. 
Description. Colour silver-white, inclining to and passing 
into steel-grey. Streak greyish black. It occurs regularly crys¬ 
tallized ; also massive and disseminated. Primary form a right 
rhombic prism. Fig. 467. M on M' 111° 18k Cleavage pa¬ 
rallel with M and M / , pretty distinct; traces parallel with P. 
Fracture uneven. Lustre metallic. Opaque. Brittle. Hardness 
from 5.5 to 6.0. Specific gravityform 5.70 to 6.20. Before 
the blowpipe, in a bulb tube, it gives a sublimate of metallic 
arsenic, and then fuses to a black bead, which, after a long continuance of the blast, becomes 
magnetic (Von Kobell). Soluble in nitric acid, with the separation of sulphur and arsenious 
acid. The solution gives an abundant blue precipitate with ferrocyanate of potassa. 
Composition. Iron 36.04, arsenic 42.88, sulphur 21.08 ( Stromeyer ). According to Beu¬ 
dant, the formula is FeS 2 + FeAs 2 . 
Geological Situation. In this State, arsenical iron pyrites has been found only in the 
primary rocks. 
LOCALITIES. 
Essex County. The massive variety, of a tin-white colour, is found in a narrow vein, 
associated with hornblende and other minerals, in the town of Lewis, about ten miles south 
of Keeseville. 
Orange County. Arsenical iron pyrites is found in various parts of this county. Per¬ 
haps the most interesting locality is that on Plopkins’ farm, near the village of Edenville. It 
is both crystallized and massive, but the crystals are too much broken to determine their form 
with accuracy. It melts alone on charcoal, with the evolution of arsenical fumes, and there 
remains a black magnetic globule. The associates are powdery red oxide of iron, scorodite, 
iron sinter, and gypsum in thin scales; the whole being imbedded in white limestone. This 
Fig. 467. 
