It is a hydrated potassium-magnesium sulfate-chloride, naturally occurring in irregular granular masses or as crystalline coatings in cavities or fissures.

This mineral is dull and soft, and is colored white, yellowish, grey, reddish, or blue to violet.

Its name is derived from Greek καινος [kainos] ("(hitherto) unknown"), as it was the first mineral discovered that contained both sulfate and chloride as anions.

Kainite is only found in comparatively few places,[7] among them in salt mines in central and northern Germany, Bad Ischl (Austria), on Pasquasia in Sicily, in Whitby (UK), and in the Carlsbad Potash District in New Mexico, in volcanic deposits in Kamchatka[8] and in Iceland,[9] and in salt lakes in western China.

Kainite is used as a source of potassium and magnesium compounds, as a fertilizer, and as gritting salt.