1.7" Red-Brown Jarosite with Calcite & Quartz - Colorado Mine, Utah

This is a small cluster of reddish-brown jarosite crystals that formed in association with quartz and calcite crystals. This mineral association was collected from the Colorado Mine in the Tintic District of Utah. There is some iridescence along one edge of the specimen.

Jarosite is the most common mineral of the alunite supergroup with a base chemical formula of KFe3+ 3(SO4)2(OH)6. The crystals are usually found as brown to amber-yellow granular crusts or coatings within cavities. The crystals are often very small: larger crystal formations are considered relatively rare. The crystals are most often found with tabular and/or pseudo-cubic structures.

Quartz is the name given to silicon dioxide (SiO2) and is the second most abundant mineral in the Earth's crust. Quartz crystals generally grow in silica-rich environments--usually igneous rocks or hydrothermal environments like geothermal waters--at temperatures between 100°C and 450°C, and usually under very high pressure. In either case, crystals will precipitate as temperatures cool, just as ice gradually forms when water freezes. Quartz veins are formed when open fissures are filled with hot water during the closing stages of mountain formation: these veins can be hundreds of millions of years old.

Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.
Jarosite, Quartz & Calcite
Colorado Mine, Tintic District, Utah
1.7 x 1.3"