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Pb9Ca5MnSi9O33
Hexagonal, P3, a = 9.82, c = 10.13 Å, Z = 1.
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| Figure 16-7. Tabular, hexagonal ganomalite crystals from Franklin. Field of view is 1.0 mm in maximum dimension. | ||
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Ganomalite was first reported from Franklin by Dunn (1979b), and the species was subsequently redefined by Dunn et al. (1985a); it had previously been considered an analogue of nasonite, in error. It was further discussed, within the context of the other lead silicates from Franklin, by Dunn (1985b).
Preliminary details of the crystal structure of Franklin ganomalite were given by Dunn et al. (1985a). There are four large-cation sites with octahedral coordination, and Mn is ordered in a site of rank 1.
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| Figure 16-8. Platy barysilite crystals epitactic on tabular ganomalite crystals from Franklin. Field of view is approximately 0.3 mm in maximum dimension. | ||
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Ganomalite occurs as simple hexagonal, tabular, 0.5 mm crystals, mostly in arrays in subparallel growth (Figures 16-7 and 16-8); additional morphological observations and illustrations were given by Yeates (1991).
It is colorless with adamantine luster; cleavage is indiscernible. There is no discernible fluorescence in ultraviolet. Local ganomalite is tentatively distinguished from nasonite by its tabular habit.
Ganomalite is a lead manganese calcium silicate mineral. Manganese was shown to be an essential constituent of ganomalite by Dunn et al. (1985a). There is little or no solid solution of other cations. An analysis is presented in Table 8.
At Franklin, ganomalite occurs in andradite, associated with nasonite and clinohedrite; few specimens are known. Ganomalite crystals occur freely-formed within vugs (Figure 16-7) and also enclosed within massive clinohedrite, the study of which revealed the coexistence of euhedral nasonite and ganomalite in contact. Aside from the above assemblage, ganomalite was seen in one anomalous specimen of the larsenite assemblage, associated with late-stage barysilite and larsenite in a vug.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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Link
to homepage
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This
page created: January 12, 2001 |
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