Iridescent Turgite

Iridescent Turgite. Iridescent Turgite. Incredible Iridescent Hematite stalactite from Graves Mountain, Georgia. Photo: Anatoly Bitny

Originally described from Turjinskii Mine (Turginsk Mine) in Russia, turgite is generally considered a variety of two more common minerals – goethite and hematite.

Turgite often referred to as a "variety" of either hematite or goethite, it is a mixture of the two minerals due to the alteration of goethite, typically found in the botryoidal habit of the "parent" goethite. It may be iridescent.
Turgite is a mixture of the two minerals due to the alteration of goethite, typically found in the botryoidal (globular) habit of the “parent” goethite; however, because it is a mixture of two minerals, it is not considered a mineral in itself.

Goethite is a common iron mineral. It often forms by weathering of other iron-rich minerals, thus is a common component of soils. It may form excellent pseudomorphs after the original minerals particularly pyrite or marcasite. Goethite may also be precipitated by groundwater or in other sedimentary conditions, or form as a primary mineral in hydrothermal deposits. When present in sufficient quantities, it constitutes an important iron ore mineral.

It apparently only occurs under specific environmental conditions because the pieces I collected in Nevada and brought home to New Mexico lost their luster and turned to dull gray hematite.

See also: The Colorful Outcrops of Turgite in New Mexico
 

Turgite coated in a cave