Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form.

It forms crystals in the isometric system very similar to normal rock salt, halite (NaCl).

[5] Sylvite is colorless to white with shades of yellow and red due to inclusions.

Massive bedded deposits occur in New Mexico and western Texas, and in Utah in the US, but the largest world source is in Saskatchewan, Canada.

Sylvite was first described in 1832 at Mount Vesuvius near Napoli in Italy and named after historical KCl designations sal degistivum Sylvii and sal febrifugum Sylvii,[7] which are named after the Dutch physician and chemist François Sylvius de le Boe (1614–1672).