Alunite is a hydroxylated aluminium potassium sulfate mineral, formula KAl<sub>3</sub>(SO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>. It was first observed in the 15th century at Tolfa, near Rome, where it was mined for the manufacture of alum. First called aluminilite by J.C. Delamétherie in 1797, this name was contracted by François Beudant three decades later<!--page 109 and 110 in the book about his travel to hungary [https://archive.org/details/travelsinhungary00beudiala] name the mineral already alunite and this book is from 1818 --> to alunite.

left|thumb|Alunite from Slovakia

Alunite crystals morphologically are rhombohedra with interfacial angles of 90° 50', causing them to resemble cubes. Crystal symmetry is trigonal. Minute glistening crystals have also been found loose in cavities in altered rhyolite. Alunite varies in color from white to yellow gray. The hardness on the Mohs scale is 4 and the specific gravity is between 2.6 and 2.8. It is insoluble in water or weak acids, but soluble in sulfuric acid.

See also

  • Acid mine drainage
  • Alum
  • Jarosite

References

  • Mineral Galleries