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Formula: Ca4MgAl4(PO4)6(OH)4.12H2O
hydrated phosphate with hydroxyl, montgomeryite group
Crystal System: Monoclinic
Specific gravity: 2.53 measured, 2.523 calculated
Hardness: 4
Streak: White
Colour: Dark green to light green, colourless, red, yellow
Environments:
Pegmatites
Hydrothermal environments
Montgomeryite is a secondary mineral in sedimentary
phosphate nodules and a
late-stage mineral in highly oxidized
phosphate nodules in granitic pegmatites (Mindat).
Localities
At the Mount Deverell variscite deposit, Milgun Station, Western Australia,
montgomeryite
occurs coating cavities in variscite veins. The
variscite deposits are hosted by marine sedimentary rocks
(AJM 20.2.27).
At the Little Green Monster Mine, Utah, USA, montgomeryite is associated with
wardite, englishite,
gordonite, crandallite and
apatite
(Dana).
At the type locality, Clay Canyon, Fairfield, Sunshine Mining District, Utah county, Utah, USA, montgomeryite
occurs in phosphate nodules in sedmimentary rocks, associated with wardite,
variscite, gordonite,
englishite and crandallite
(Mindat).
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