JAROSITE, a mineral species consisting of hydrous potas sium and aluminium sulphate, and often occurring as incrustations of minute indistinct crystals with a yellowish-brown colour and brilliant lustre. The best specimens, consisting of crystalline crusts on limonite, are from the Jaroso ravine in the Sierra Al magrera, province of Almeria, Spain, from which locality the mineral receives its name. It appears to be a common product
of decomposition of sulphides in mineral veins, and one variety, from Nevada and New Mexico, plumbojarosite, contains lead.