Kainite, formula- [KMg(SO4)Cl·3H2O] is an evaporite mineral in the class of “Sulfates (selenates, etc.) with additional anions, with H2O” according to the Nickel-Strunz classification. It is a naturally occurring double salt, hydrated potassium, and magnesium sulfate-chloride. It is a natural salt consisting of a hydrous sulfate and chloride of magnesium and potassium that is used as a fertilizer and as a source of potassium and magnesium compounds.
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 forms monoclinic crystals.
- Category: Sulfate minerals
- Formula: [KMg(SO4)Cl·3H2O]
- Crystal system: Monoclinic
- Crystal class: Prismatic (2/m) (same H-M symbol)
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.
- Color: Colorless; yellow, brownish, greyish-green, red, violet, blue
- Crystal habit: Crystal aggregates, fibrous, massive
- Fracture: Splintery
- Tenacity: Brittle
- Mohs scale hardness: 2.5-3
- Luster: Vitreous
- Streak: White
- Diaphaneity: Transparent
- Specific gravity: 2.15
Kainite was discovered in the Stassfurt salt mines in today’s Saxony-Anhalt, Germany in 1865 by the mine official Schöne and was first described by Carl Friedrich Jacob Zincken.
Kainite is a typical secondary mineral that forms through a metamorphosis in marine deposits of potassium carbonate and is also occasionally formed through resublimation from volcanic vapors. It is often accompanied by anhydrite, carnallite, halite, and kieserite.
Association: Sylvite, halite, carnallite, kieserite, polyhalite, langbeinite, picromerite
Uses – Kainite is used as a source of potassium and magnesium compounds, as a fertilizer, and as gritting salt.