3.9" Red-Brown Jarosite Crystals on Barite - Colorado Mine, Utah
This is a cluster of reddish-brown jarosite crystals that formed on bladed barite crystals. This mineral association was collected from the Colorado Mine in the Tintic District of Utah. There is a small aggregation of calcite crystals along one edge of this cluster.
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, with larger crystal formations being considered relatively rare. The crystals are most often found with tabular and/or pseudo-cubic structures.
Barite, commonly spelled baryte, is well-known for its great range of colors and varied crystal forms and habits. It is a heavy mineral consisting of barium sulfate, and typically has the chemical formula of BaSO4. The barite group consists of baryte, celestine, anglesite and anhydrite. It's generally white to colorless and is the main source of barium.
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.