Acuminite

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Acuminite
General
Category Halide mineral
Formula
(repeating unit)
SrAlF4OH·(H2O)
Strunz classification 03.CC.10
Crystal symmetry Monoclinic 2/m or m
Unit cell a = 13.223 Å, b = 5.175 Å, c = 14.251 Å; β = 11.61°; Z = 8
Identification
Color White
Crystal habit Clusters of acute dipyramidal Spearhead shaped crystals
Twinning Contact on {100}
Cleavage Perfect on {001}
Mohs scale hardness 3.5
Luster Vitreous
Diaphaneity Transparent
Specific gravity 3.295
Optical properties Biaxial (+)
Refractive index nα = 1.451 nβ = 1.453 nγ = 1.462 - 1.463
References [1][2][3]

Acuminite is a rare halide mineral of with chemical formula: SrAlF4(OH)·(H2O). Its name comes from the Latin word acumen, meaning "spear point". Its Mohs scale rating is 3.5.

Acumenite has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.[1]

References[edit]