Kalsilite: Properties and Occurrences

Kalsilite (KAlSiO4) is a vitreous white to the grey feldspathoidal mineral that is found in some potassium-rich lavas, such as from Chamengo Crater in Uganda. It is a rare mineral consisting of aluminosilicate of potassium. It has a relative hardness of 5.5.

General information:

  • Formula: KAlSiO4
  • Crystal System: Hexagonal
  • Member of: Feldspathoid Group
  • Type Locality: Kamengo, Gomba District, Central Region, Uganda

Fig: Kalsilite

Properties

  • Cleavage: {1010} Indistinct, {0001} Indistinct
  • Color: Colorless, Gray, Gray white, White.
  • Density: 2.59 – 2.625, Average = 2.6
  • Diaphaneity: Transparent to Translucent
  • Fracture: Brittle – Conchoidal – Very brittle fracture producing small, conchoidal fragments.
  • Hardness: 6 – Orthoclase
  • Luster: Vitreous – Greasy
  • Streak: white

Occurrence: In the groundmass of some potassium-rich and silica-de¯cient lavas and tu®s; rare in syenites; may be formed by the breakdown of silica-rich leucite in alkalic ultrama¯c rocks; from a granulite-facies emery deposit.

Association: Olivine, melilite, clinopyroxene, phlogopite, nepheline, leucite.