(mineralogy) Amineral usually occurring infibrous masses, of a brick-red color, being tinged with iron, and consisting chiefly of the sulphates oflime,magnesia, andsoda.
2019 October, James Abbott, “Esk Valley revival”, inModern Railways, page76:
Shafts are now being sunk at Sirius Minerals' Woodsmith mine to extractpolyhalite for use as an agricultural fertiliser, with much of the output exported.
