PARABRANDTITE

Ca₂Mn(AsO₄)₂.2H₂O 
Triclinic, P1 or P1, a = 5.89, b = 7.031, c = 5.64 Å,
a = 96.77, b = 109.32, g = 108.47^o,  Z = 1

	Figure 25-31. Parabrandtite crystals in parallel growth from Sterling Hill. Field of view is 0.4 mm in maximum dimension.

Parabrandtite, first thought to be talmessite, was described from Sterling Hill by Dunn et al. (1987c). It has not been found at Franklin.

Description

Parabrandtite occurs as stout, colorless, 1-2 mm aggregates of crystals which occur in parallel growth (Figures 25-31 and 25-32); the quality of available crystals did not permit goniometric measurement of the crystal forms.

Parabrandtite is transparent, has perfect cleavage on {010} and {110}, vitreous luster, and a density of 3.55 g/cm³ (meas.), 3.60 g/cm³ (calc.) Optically, parabrandtite is biaxial, positive, 2V = 79.9^o, with a = 1.701, b = 1.721, and g = 1.751; dispersion is weak, r > v.

	Figure 25-32. Parabrandtite crystals in parallel growth from Sterling Hill. Field of view is 1.0 mm in maximum dimension.

The optical orientation is given in detail by Dunn et al. (1987c). There is no discernible fluorescence in ultraviolet. It is best verified using X-ray and chemical methods.

Composition

Parabrandtite is a calcium manganese arsenate hydrate mineral and the Mn nalogue of talmessite. A microprobe analysis is given in Table 25, showing minimal substitution of other cations.

Occurrence and paragenesis

Parabrandtite occurs at Sterling Hill, forming crystals in a cavity in franklinite/red-willemite/calcite  ore. It is associated with sarkinite and was found but once.

Name

Parabrandtite is named for its close relation to brandtite.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 11, 2001