What is Leucite?
Leucite is a potassium aluminium silicate feldspathoid of silica-undersaturated volcanic rocks, often preserved as pale trapezohedral crystals.
Mineralogy and crystal structure
Reference formula: KAlSi2O6. Leucite is tetragonal at ordinary temperature but derives from a higher-temperature cubic framework. It is a feldspathoid rather than a feldspar, and its low density and volcanic associations help distinguish it from visually similar pale minerals. Leucite is classified with silicates and has a tetragonal crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 2.4–2.5.
Colour, lustre and habit
Typical colours include white, colourless, grey, cream. The usual trapezohedral, granular, spherical habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Leucite forms in or is associated with potassium-rich, silica-undersaturated lavas and shallow volcanic rocks. Important documented localities include Italy, Germany, Uganda, Tanzania, the United States and Canada.
A geometric feldspathoid from alkaline lava
Leucite is an excellent display mineral for showing how unusual magma chemistry changes the minerals that crystallise. Pale trapezohedral forms, a light visual presence and classic Italian localities give it understated but unmistakable collector appeal.
Collecting and care
Protect crystal faces and matrix from abrasion; retain the volcanic context because weathering can alter or replace leucite.
