PYROPHANITE

MnTiO₃ 
Hexagonal, R3, a = 5.161, c = 14.317 Å, Z = 2

Pyrophanite was first reported from Sterling Hill by Sandhaus (1981) and Craig et al. (1985) and was later reported by Valentino (1983) and Valentino et al. (1990). It has not been reported from Franklin.

Description

Pyrophanite occurs as subhedral aggregates or microscopic grains up to 2 mm in diameter, but most are much smaller. They are black, opaque, and have metallic luster. Reflectance and microhardness data were given by Craig et al. (1985).

Composition

Pyrophanite is a manganese titanium oxide mineral and the Mn-analogue of ilmenite. Craig et al. (1985) reported four closely agreeing analyses, with approximately 2.5 wt.% FeO and 1.6 wt. % ZnO and trace amounts of Si, Al, K, Na, and Ca. Valentino (1983) reported similar Zn-concentrations, but with markedly higher Fe contents; he also presented a discussion of contamination possibilities. Therefore, to date, there is little evidence of solid solution toward ZnTiO₃, such as was found in China by Suwa et al. (1987).

Occurrence and paragenesis

The occurrence reported by Sandhaus (1981) and Craig et al. (1985) was found near the 500 level of the Sterling mine. The matrix is greenish-gray Mn-bearing augite associated with gahnite, hendricksite, and calcite. Pyrophanite occurs within the augite.

Valentino (1983) and Valentino et al. (1990) reported pyrophanite exsolved in magnetite lamellae, which are themselves part of a magnetite-franklinite exsolution. His specimens were also found on the 500 level at Sterling Hill, approximately 10 feet east along the cross-cut from the west limb. The rock at this site is marble containing diopside, franklinite, gahnite, mica, and garnet.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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