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Formula: Ca3Be2(PO4)2(PO3OH)2.4H2O
Hydrated phosphate, beryllium-bearing mineral
Crystal system: Monoclinic
Specific gravity: 2.56 measured, 2.53 calculated
Hardness: 3
Streak: White
Colour: Colourless to slightly whitish
Luminescence: Not fluorescent under UV
Environments
Pegatites
Hydrothermal environments
Although fransoletite was approved in 1982, to date (October 2025) it has been reported only from the
type locality.
Localities
At the type locality, the Tip Top Mine, Fourmile, Custer Mining District, Custer County, South Dakota, USA,
fransoletite formed by late-stage hydrothermal alteration of beryl and
other phosphates in a zoned granite
pegmatite. Associated minerals include
beryl, tiptopite,
whitlockite, carbonate-rich
apatite, montgomeryite,
hurlbutite, englishite,
roscherite and quartz
(HOM).
Fransoletite from the Tip Top Mine -
Image
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