Calcium larsenite

Character
Calcium larsenite is white and opaque, with a greasy luster, and the cleavage is indistinct. Its specific gravity is 4.421. Under the iron-are it shows a strong lemon-yellow fluorescence, more vivid than and easily distinguished from that of willemite and so strong that the mineral can be instantly detected. A specimen of hardystonite collected by Professor Wolff at the Parker shaft before 1898 was thus shown to contain calcium larsenite.

Hardly any calcium larsenite found is fresh, because it alters easily on exposure and becomes darker. The darkening is possibly due to the separation of native lead (?), which Bauer has found associated with calcium larsenite. A specimen in the Harvard collection shows a fresh core of calcium larsenite surrounded by a thick dark-brown zone of altered material.

The mineral is optically biaxial and negative. The material analyzed was almost uniaxial, as 2V = 5° , and a = 1.760 and b = g = 1.769, all ±0.001. Another sample, apparently fresher than the analyzed material, gave 2V = 40° , and a = 1.762, b = 1.770, and g = 1.774 (Berman).

Composition
Calcium larsenite is an orthosilicate of calcium, lead, and zinc.

**Analysis of calcium larsenite**
	1	2
SiO₂	24.10		0.401
FeO	0.48
MnO	0.57
CaO	16.36	0.292*	0.792
ZnO	30.61	0.376*
PbO	27.63	0.124*
MgO	0.23
H₂O	0.12
	100.10

[*figures reflected in the value 0.792 shown]

1. Calcium larsenite. L. H. Bauer (256), analyst.

2. Molecular ratio of essential constituents.

Occurrence
Calcium larsenite was found at Franklin, closely associated with larsenite, as described under that mineral. It was also found later in the 1,100-foot level in pillar 80, replacing a mixture of hardystonite and glaucochroite with franklinite.


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	This page created: August 12, 2006 5:50 PM