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CaMg(AsO4)F
Monoclinic
Tilasite was reported from Sterling Hill by Parker (1978); it is not known from Franklin.
Tilasite occurs as 4 mm, euhedral, milky white crystals with a slightly pearly luster. It fluoresces with a whitish-yellow color in shortwave ultraviolet. No physical or optical data exist.
Tilasite is a calcium magnesium fluorine arsenate mineral, closely related to adelite. A microprobe analysis by the writer yielded CaO 26.11, MgO 18.84, As2O5 51.51, F 6.85, less O = F 2.88, total = 100.43 wt. %.
Tilasite occurs as crystals on a reddish-brown seam of friedelite, associated with barite and calcite in red-willemite ore, and as a milky white coating mixed with white willemite on red-willemite/franklinite ore at Sterling Hill.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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Link
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This
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