POWELLITE

CaMoO₄
Tetragonal

Powellite, a calcium molybdate mineral and the molybdenum analogue of scheelite, occurs at both Franklin and Sterling Hill. It is commonly colorless to very light greenish-yellow with greasy to adamantine luster and fluoresces with a moderate yellow color in shortwave ultraviolet and a weaker yellow in longwave. It occurs as alterations of molybdenite crystals at both deposits.

At Franklin, powellite is associated with microcline, willemite, apatite, molybdenite, and calcite, in a light-colored rock. Semiquantitative analysis of two specimens from this Franklin occurrence yielded, respectively and approximately, CaO 24 and 23 wt. %, WO₃ 31 and 43 wt. %, and MoO₃ 41 and 31 wt. %, showing that this material has Mo > W in both specimens and is a tungstenian powellite. A possibly distinct assemblage of powellite with scapolite and molybdenite has also been found on the Buckwheat Dump.

At Sterling Hill, powellite occurs in several assemblages. It is found with epidote and sphalerite on a thin vein in gneiss. Semiquantitative analysis of this material yielded a composition of approximately CaO 25 wt. %, WO₃ 29 wt. %, and MoO₃ 44 wt. %. It was also found with hedenbergite, molybdenite, calcite, and red-fluorescing feldspar in the hanging wall of the black-willemite ore on the 430 level; this material has not been chemically analyzed by the writer. In 1990, powellite with 70 mole % of the end-member was found on the 340 level at Sterling Hill with wollastonite (P. Modreski, pers. comm.).

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