Ferroschallerite

Physical character
Ferroschallerite is found only in coarse grains having perfect cleavage in a single direction. One such grain shows a rudely hexagonal outline in such relation to the cleavage as to indicate a prismatic form and pinacoidal cleavage; hence there is little doubt that the mineral is hexagonal. The grains reach a maximum diameter of half an inch.

Ferroschallerite is yellowish-brown to clove-brown, with a pearly luster on the cleavage. Some grains are clear and glassy. The hardness is about 5, and the specific gravity is 3.44. It is optically uniaxial and negative; w = 1.718, e = 1.700.

Composition
The chief difference between schallerite and ferroschallerite chemically is that in the latter mineral ferrous iron takes the place of about half the manganese of the former. Hence the two are related chemically much as are friedelite and pyrosmalite. The formula of ferroschallerite derived from the analysis is (Mn,Fe,Zn)₈[(SiO₃)₆(OH)(As₂O₅).₇₅].3H₂O in which Mn is to Fe as 2 to 1.

**Analysis of ferroschallerite**
	1	2
SiO₂	31.12	31.38
MnO	29.22	30.94
FeO	17.12	15.69
MgO	0.12
ZnO	3.63	3.55
As₂O₅	12.46	12.94
H₂O	6.42	5.50
	100.09	100.00

1. Ferroschallerite, Franklin. L. H. Bauer (273), analyst.

2. Composition computed from the formula adopted.

Occurrence
All the specimens of ferroschallerite known seem to have been collected by the late George Stanton in 1925 in the mine at Franklin, in pillar 1597, about 50 feet south of the old Trotter shaft. There are three types of association—as coarse clear grains with coarse prisms of zinc cummingtonite in calcite, as a layer of grains between zinc cummingtonite and fibrous gray willemite, and as a layer of grains between coarse crystals of zinc cummingtonite and granular feldspar. The specimens suggests the contact phases of one of the abundant pegmatite masses of that part of the mine.


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	This page created: January 12, 2001 6:15 PM