Alunite

Alunite (hydrated aluminum potassium sulfate) is a naturally occurring mineral containing alum.  The name “alum” is used for several different compounds, but usually refers to the double sulfate salt of aluminum and either potassium, ammonium, or sodium.  Most commonly, it refers to potassium alum. Alum has been in use since antiquity, and it is still widely used today in industry as a mordant in dyeing, in tanning, in making paper and baking powders, as a flocculant to purify piped water, and to fireproof paper and cloth.  Alum is commonly used as a styptic to stop the bleeding of minor wounds, and an astringent. Styptic pencils and alum blocks were once common items in men’s shaving kits.