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K(Mg,Fe)3(Al,Fe3+)Si3O10(OH)2
Monoclinic
Biotite, a potassium magnesium iron aluminum silicate hydroxide mineral of the mica group, was described from Sterling Hill by Frondel and Einaudi (1968). They reported a number of analyses of zincian manganoan biotites; several of these are given in Table 13. They reported biotite associated with franklinite, rhodonite, calcite, pyroxene, apatite, and fluorite. Hendricksite and biotite, associated with many of the same minerals, cannot be visually distinguished as to species. Biotite is commonly black, with perfect {001} cleavage, and vitreous luster. It may be a constituent of silicate assemblages in the magnetite occurrences, and it is found in the local gneisses. Johnson (1990) gave the chemical composition of a biotite from the Sterling Hill gneiss zone, which was also subjected to K-Ar age dating with a result of 883 (±35) million years. Biotite has not been reported from Franklin.
Barian biotites from Sterling Hill were reported by Reilly (1983) who provided 7 analyses and found BaO values from 7-21 wt. %, the latter representing about 84 mole % of the barium analogue of biotite. This barian biotite is associated with calcite and diopside; additional data and discussion were given by Tracy (1991).
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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This
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