Polyhalite

Symbol	K2Ca2Mg(SO4)4·2H2O

A naturally occurring evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium, used once crushed directly as a multi-nutrient fertiliser (marketed as POLY4) without further chemical processing.

Mines

Mine	Region	Worked
Woodsmith Mine	North Yorkshire	from Under construction since 2017 (not yet in production)