Acuminite

acuminite

gearksutite

thomsenolite

cryolite

Formula:SrAlF4(OH).H2O
Halide, paramorph of tikhonenkovite. strontium-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.295 measured, 3.305 calculated
Hardness: 3½
Streak: White
Colour: Colourless, white, becomes yellow on exposure to x-rays (Mindat)
Common impurities: Ca
Environments

Pegmatites

The only reported occurrence of acuminite is at the type locality, the Ivigtut Cryolite deposit, Sermersooq, Greenland, Denmark, where occurs in a small cavity in a specimen from a strontium-rich portion of the cryolite deposit, associated with celestine, fluorite, jarlite, thomsenolite, hydrokenoralstonite, pachnolite and gearksutite (Mindat, Dana, HOM, AM 73.1492).

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