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

Acuminite
General
CategoryHalide mineral
Formula
(repeating unit)
SrAlF4OH·(H2O)
IMA symbolAcu[1]
Strunz classification3.CC.10
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 13.223, b = 5.175
c = 14.251 [Å]; β = 11.61°; Z = 8
Identification
ColorWhite
Crystal habitClusters of acute dipyramidal Spearhead shaped crystals
TwinningContact on {100}
CleavagePerfect on {001}
Mohs scale hardness3.5
LusterVitreous
DiaphaneityTransparent
Specific gravity3.295
Optical propertiesBiaxial (+)
Refractive indexnα = 1.451 nβ = 1.453 nγ = 1.462 - 1.463
References[2][3][4]

Acumenite has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.[2]

See also

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Handbook of Mineralogy
  3. ^ Mindat.org
  4. ^ Webmineral data