PYROBELONITE

PbMn(VO₄)(OH)
Orthorhombic

	Figure 25-33. Prismatic, pyramidal crystals of pyrobelonite from Franklin. Field of view is 0.5 mm in maximum dimension.

Pyrobelonite was first noted by Palache (1935) who described it as descloizite from Franklin; it was subsequently found to be pyrobelonite (Dunn, 1983a), which is unknown from Sterling Hill.

Description

Pyrobelonite occurs as bright red, prismatic, tapering, 0.3 mm crystals. The color is similar to that of proustite, but pyrobelonite lacks the submetallic luster of that species. The crystals taper gradually to a point (Figures 25-33 and 25-34) and on casual examination appear to be tiny zincite crystals. No physical or optical data have been obtained; the mineral was verified by X-ray methods and chemical analysis, which are suggested for verification.

Composition

Pyrobelonite is a lead manganese vanadate hydroxide mineral related to descloizite (perhaps explaining Palache’s incorrect assignment of species). A microprobe analysis yielded CaO 0.3, FeO 0.3, ZnO 0.4, MnO 18.7, PbO 54.3, SiO₂ 2.2, V₂O₅ 20.3, with H₂O from the theoretical composition at 2.3, total = 98.8 wt. %.

Occurrence and paragenesis

	Figure 25-34. Prismatic pyramidal crystals of pyrobelonite from Franklin. Field of view is 0.6 mm in maximum dimension. See figure 12-43.

Pyrobelonite occurs on willemite/franklinite ore which is encrusted with a druse of andradite and isolated crystals of tephroite (Figure 15-3), clinochlore, and willemite. Pyrobelonite occurs as a sprinkling of tiny red crystals on all these minerals and is in turn coated with hodgkinsonite of unusual habit (Figure   15-52) and barite. Few specimens of this superb assemblage (Figure 12-43) are known; the richest specimen is at Harvard University. 

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