What is Kalsilite?
Kalsilite is a potassium aluminium silicate of silica-undersaturated volcanic rocks, a specialist mineral that reveals the chemistry of alkaline magmas.
Mineralogy and crystal structure
Reference formula: KAlSiO4. Kalsilite has a hexagonal feldspathoid framework and is chemically related to nepheline, but its ordering and symmetry differ. It is often fine-grained, so the host lava and analytical context are important. Kalsilite is classified with silicates and has a hexagonal crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 2.6–2.7.
Colour, lustre and habit
Typical colours include colourless, white, grey, yellowish. The usual granular, prismatic, massive habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Kalsilite forms in or is associated with nepheline-bearing lavas, alkaline volcanic rocks and high-temperature feldspathoid assemblages. Important documented localities include Italy, Uganda, Tanzania, Canada, Russia and the United States.
A specialist feldspathoid with a strong volcanic story
Kalsilite is a rewarding choice for a collection that goes beyond familiar quartz and feldspar. Its quiet appearance opens a route into alkaline volcanism, silica undersaturation and the unusual framework structures formed by potassium and aluminium.
Collecting and care
Protect small grains and matrix surfaces from abrasion; retain locality information because hand specimens can be visually understated.
