1911 Encyclopædia Britannica/Jarosite

by Leonard James Spencer

JAROSITE, a rare mineral species consisting of hydrous potassium and aluminium sulphate, and belonging to the group of isomorphous rhombohedral minerals enumerated below:—

Alunite	K2	[Al(OH)2]6(SO4)4
Jarosite	K2	[Fe(OH)2]6(SO4)4
Natrojarosite	Na2	[Fe(OH)2]6(SO4)4
Plumbojarosite	Pb	[Fe(OH)2]8(SO4)4

Jarosite usually occurs as drusy incrustations of minute indistinct crystals with a yellowish-brown colour and brilliant lustre. Hardness 3; sp. gr. 3.15. The best specimens, consisting of crystalline crusts on limonite, are from the Jaroso ravine in the Sierra Almagrera, province of Almeria, Spain, from which locality the mineral receives its name. It has been also found, often in association with iron ores, at a few other localities. A variety occurring as concretionary or mulberry-like forms is known as moronolite (from Gr. μῶρον, “mulberry,” and λίθος, “stone”); it is found at Monroe in Orange county, New York. The recently discovered species natrojarosite and plumbojarosite occur as yellowish-brown glistening powders consisting wholly of minute crystals, and are from Nevada and New Mexico respectively.  (L. J. S.)