Acuminite: General Information with Properties

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.

The term acuminite was coined from the Latin word acuminis, meaning sharp point, or spear head, to denote the characteristic shape of the crystals in the mineral. It is an aluminum complex salt. It has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.

General information:

  • Category: Halide mineral
  • Formula: SrAlF4(OH)·(H2O).
  • Strunz classification: 3.CC.10
  • Crystal system: Monoclinic

Acuminite occurs in a small cavity in a specimen from a strontium-rich portion of a cryolite deposit. It is often associated with minerals such as pachnolite, fluorite, ralstonite, gearksutite, celestine, jarlite, and thomsenolite.

Physical properties

  • 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

How to identify:

Acuminite can be identified in the field by its colorless structure, with white streak, and vitreous luster. The densityis 3.295 g/cm³, with a hardness of 3.5 – approximate to a copper penny.

Health Risks: No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

 

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