Calamine

Habit
Isolated crystals of calamine are rare, and none showing double termination were observed. The crystals are generally grouped in subparallel or radiate fashion, forming fan-shaped, crested, stalactitic, or mammillary aggregates. The crested masses, illustrated in plate 16, C, are coarsely to finely crystalline and form the surfaces of large flat slabs or of coarse stalactites. From their characteristic appearance they are known among the zinc miners as "maggot ore." Calamine is also found in compact fibrous and chalky coatings. Its color is snow-white in masses, but much of it is stained brown or yellow by ferruginous clay. It is rarely bluish and transparent or colorless.

No measurable crystals were discovered by the author among the many specimens examined, and the only crystallographic data on Franklin calamine, are those given by Pratt (158).

Composition
Calamine is a basic zinc silicate having a chemical structure analogous to that of clinohedrite. The white crystallized calamine is almost absolutely pure, as shown by analysis 1, below. The massive forms are mixed with clay, and the analyses (page 106) indicate that the so-called "vanuxemite" of Shepard (110) is merely a mixture of equal parts of calamine and of clay of the composition of halloysite: H₄Al₂Si₂O₉+H₂O.

Occurrence
Calamine has been found at Franklin only in minor amount, associated with the altered sphalerite in small cross veins secondary to the main ore body. In such a small vein, exposed in 1905 in the east wall of the Buckwheat open cut, radiate clusters of minute thin-tabular transparent crystals of calamine were found, attached to the limonite coated quartz of which the vein was mainly composed. Remnants of sphalerite in the cavities showed that that mineral was probably the source of the calamine. Nowhere on Mine Hill do conditions seem to have been favorable to the formation or rather to the preservation of calamine, which, however, may have been formed from the primary zinc minerals.

The great masses of calamine discovered at Sterling Hill have been fully described on pages 22-23.

**Analyses of calamine**
	1	2	3	4
SiO₂	24.15	24.95	34.50	34.25
Al₂O₃	0.19*		18.40	18.45
Fe₂O₃
ZnO	67.55	67.58	33.24	33.75
CaO	0.12
H₂O	7.95	7.47	13.67	13.55
	99.96	100.00	99.81	100.00

[* figure represents combined Al₂O₃ + Fe₂O₃.]

1. White calamine, Sterling Hill. Clarke and Steiger (182), analysts.

2. Composition computed from the adopted formula.

3. Vanuxemite, Sterling Hill. C. W. Cross (113), analyst.

4. Computed composition of a mixture of equal parts of calamine and halloysite.


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