White or gray mineral

Wikipedia Word definitions in Wikipedia
Leucite is a rock -forming mineral composed of potassium and aluminium tectosilicate K[AlSiO]. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 1821, they are not optically isotropic, and are therefore pseudo-cubic. ...

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Leucite \Leu"cite\ (l[=u]"s[imac]t), n. [Gr. leyko`s white: cf. F. leucite.] (Min.) A mineral having a glassy fracture, occurring in translucent trapezohedral crystals. It is a silicate of alumina and potash KAlSi2O6 . It is found in the volcanic rocks ...

Wiktionary Word definitions in Wiktionary
n. 1 (label en mineralogy) A mineral of silica-poor igneous, plutonic and volcanic rocks. Chemically, leucite is a potassium feldspar with insufficient silica to satisfy the chemical bonds. Because of the unfilled bonds, leucite weathers rapidly and can ...