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KCa4Si8O20(F,OH).8H2O
Tetragonal
Fluorapophyllite occurs at Franklin and was first described (as apophyllite) by Palache (1935). Frondel (1972) reported a Sterling Hill occurrence of apophyllite, undifferentiated as to species; this material has not been examined.
Fluorapophyllite occurs as euhedral, highly lustrous crystals, up to 15 mm in size, tabular on [001], and as clusters of such crystals slightly offset from one another. It is white to pink to off-white and has a perfect cleavage on {001}, which exhibits a pearly luster; it has a vitreous luster on crystal faces and fracture surfaces. No physical or optical measurements have been made. The material resembles common fluorapophyllite in every way. There may be no discernible fluorescence in ultraviolet.
Fluorapophyllite is a potassium calcium silicate fluorine hydrate mineral. Partial microprobe analysis of the crystals described above yields: SiO2 50.9, CaO 24.6, K2O 4.2, Na2O 0.4, F 1.9, less O=F 0.8 wt. %, indicating that this material is near the fluorine end-member in the fluorapophyllite-hydroxyapophyllite series.
Franklin fluorapophyllite was described by Palache (1935) as occurring in the gneissic footwall of the Palmer Shaft at 600 feet on the incline. Bauer’s catalogue indicates the specimens were found in 1907. Much of this material has been preserved, and it is found in many local collections. The matrix for most specimens is hedenbergite and epidote, associated with pyrite, ferroaxinite, zircon, natrolite, calcite, and other minerals. The assemblage is described in detail by Betancourt (1989).
Other occurrences may exist, but have not been studied. Lovely 6 mm clusters of light pink crystals, undifferentiated as to species, are labeled in the Harvard collection as being from the 910 pillar, 900 level, 35 feet from the footwall and near the Palmer Shaft. Fine 1-2 mm light pink crystals were found in 1990 on the 340 level at Sterling Hill; they have not been analyzed for fluorine or water.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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