Alunite, or alumstone, is a
mineralthat was first observed in the 15th centuryin Monti della Tolfa, north to Rome, where it was mined for the manufacture of alum. First called "aluminilite" by J.C. Delametherie in 1707, this name was contracted by François Beudant in 1824 to alunite.
crystals of alunite are rarely found in cavities in the massive material. Alunite crystallizes in the hexagonalsystem with crystals forming trigonalpyramids that resemble rhombohedra with interfacial angles of 90 50', so that they resemble cubes in appearance. Minute glistening crystals have also been found loose in cavities in altered rhyolite. Alunite varies in color from white to yellow gray. The hardnessis 4 and the specific gravityis between 2.6 and 2.8. The mineral is a hydrated aluminium potassium sulfate, KAl3(SO4)2(OH)6. Sodium substitutes for potassium and when high in sodium it is called natroalunite. It is insoluble in water or weak acids, but soluble in sulfuric acid. Jarositeis an iron analogue in which Fe3+ replaces the aluminium. It occurs as a secondary mineral on iron sulfate ores.
Alunite occurs as veins and replacement masses in
trachyte, rhyolite, and similar potassium rich volcanic rocks It is formed by the action of sulfuric acidbearing solutions on these rocks during the oxidationand leaching of metal sulfide deposits. Alunite also is found near volcanic fumaroles. The white, finely granular masses closely resemble finely granular limestone, dolomite, anhydrite, and magnesitein appearance. The more compact kinds from Hungary are so hard and tough that they have been used for millstones.
Historically extensive deposits were mined in
Tuscanyand Hungary, and at Bulahdelah, Australia. Currently found at Tolfa, Italy. In the United States it is found in the San Juan district of Colorado; Goldfield, Nevada; the ghost townof Alunite, Utahnear Marysvale; and Red Mountain in Patagonia, Arizona. The Arizona occurrence lies appropriately above a canyon named "Alum Gulch". Alunite is mined as an ore of both potassium and aluminium at Marysvale. Some of the oredeposits were located by airborne and satellite multispectral imaging.
*cite book|last=Hurlbut|first=Cornelius S.|year=1966 |title=Dana's Manual of Mineralogy|edition=17th ed.|id=ISBN 0-471-03288-3
*cite book|last=Hurlbut|first=Cornelius S.|coauthors =Cornelis Klein|year=1985|title=Manual of Mineralogy|edition=20th ed.|id=ISBN 0-471-80580-7
* [http://mineral.galleries.com/minerals/sulfates/alunite/alunite.htm Mineral Galleries]
* [http://webmineral.com/data/Alunite.shtml Webmineral]
* [http://www.mindat.org/min-161.html Mindat]
Wikimedia Foundation. 2010.