PENNANTITE-1a

Mn₅Al(Si₃Al)O₁₀(OH)₈ 
Monoclinic, a = 5.41, b = 9.40, c = 14.34 Å, b = 96.8^o

Pennantite was found at Franklin by the writer, but has not been found at Sterling Hill. The unit-cell given above is from Bayliss (1983).

Description       

Franklin pennantite occurs as thin platy layers of 1 mm crystals in several different assemblages. Some pennantite-1a appears to be epitactically grown on willemite. It is dark red, sometimes reddish-brown, with vitreous luster and a perfect cleavage. The hardness and texture is that of a chlorite. Subspherical aggregates are common. There is no discernible fluorescence in ultraviolet.

Composition

Pennantite is a manganese aluminum silicate hydroxide mineral of the chlorite group. The composition of Franklin material, determined by the writer and published by Bayliss (1983) is: SiO₂ 23.9, Al₂O₃ 19.1, Fe₂O₃ 2.6, MgO 3.4, ZnO 15.9, MnO 27.4 wt. %.

Occurrence and paragenesis

Pennantite was first described from Franklin as “a Mn-chlorite” by Dunn et al., (1983a). It coats secondary willemite crystals, and is associated with prehnite, datolite, roeblingite, charlesite, and numerous other species in a highly hydrated, recrystallized assemblage.

Copyright © 1995 by Pete J. Dunn			Website by Herb Yeates
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This page created: January 14, 2001