Poughite
Chemical formula: Fe<sup>3+</sup><sub>2</sub>(Te<sup>4+</sup>O<sub>3</sub>)<sub>2</sub>S<sup>6+</sup>O<sub>4</sub>·3H<sub>2</sub>O
Poughite is a very rare, hydrated iron sulfate-tellurite, forming small, platy crystals of an intensely yellow or brownish color.
Description
## Characteristics Poughite is a mineral from the sulfate and tellurite group, valued for its appearance and rarity. It occurs as small, thin to thick, platy crystals with a square or rectangular outline. These crystals often form fan-shaped or rosette aggregates, which are most sought after by collectors. Its color is characteristic and ranges from honey-yellow, through yellowish-brown, to reddish-brown. ## Physical Properties This mineral is relatively soft, with a hardness of about 2.5 on the Mohs scale. It is characterized by a strong, adamantine luster, which gives it a vibrant appearance, especially in well-formed crystals. It is transparent to translucent. Its density is about 4.11 g/cm³, which is a relatively high value, typical for minerals containing heavy elements like tellurium. ## Colors and Varieties Poughite does not form named varieties. Its color palette is consistent and includes shades from intensely yellow to reddish-brown. The variability in coloration depends on minor impurities and crystallization conditions. ## History and Name The mineral was first described in 1967. Its name honors Frederick Harvey Pough (1906-2000), an American mineralogist and curator of mineralogy at the American Museum of Natural History in New York. The type locality, from which the research material originated, is the El Plomo mine in Honduras. ## Applications Due to its extreme rarity and small crystal sizes, poughite has no industrial applications. It is solely an object of scientific interest and a prized acquisition in advanced collections of rare minerals and micromount specimens.
Diagnostic features
## Identification Characteristic features of poughite include its platy crystal form, often in rosettes, intense yellowish-brown color, and strong, adamantine luster. A key indicator is its occurrence environment – oxidation zones of tellurium-rich deposits – and co-occurrence with other rare tellurites and tellurides. ## Distinguishing from Similar Minerals Poughite can be confused with other yellow secondary tellurium minerals, such as emmonsite or paratellurite. Emmonsite most often forms fibrous or acicular aggregates, in contrast to platy poughite. Final differentiation from similar, very rare minerals requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Poughite crystals are thin to thick-platy, with a square or rectangular outline. They most often occur as fan-shaped or radial aggregates, forming characteristic "rosettes" on the surface of the host rock.
Geological environment
## Genesis Poughite is a secondary mineral. It forms in the oxidation zones (so-called iron caps) of hydrothermal ore deposits rich in tellurium. It is formed as a result of the weathering of primary tellurides and sulfides under strongly acidic and oxidizing conditions. ## Mineral Associations This mineral often occurs in association with other secondary tellurium minerals. The most common associations include emmonsite, tellurite, as well as native tellurium, pyrite, and quartz. ## Localities It is a very rare mineral, known from only a few localities worldwide. Besides the type locality in the El Plomo mine in Honduras, high-quality specimens come from the Bambolla mine in Moctezuma (Sonora, Mexico) and the Trixie mine in the Tintic Mountains (Utah, USA). It is also known from the Kawazu mine in Japan.
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly valued poughite specimens are those with sharply defined, well-formed crystals creating aesthetic rosettes. The intensity and purity of the honey-yellow color also significantly increase its value. Due to the small size of the crystals, size is a crucial factor – larger, well-formed aggregates are extremely desirable. The value of a specimen increases if it occurs in association with other rare tellurium minerals. ## Popular Localities The best specimens in the world are considered to come from the Bambolla mine in Mexico and the Trixie Mine in Utah, USA. They are characterized by exceptionally well-formed crystals and intense color. Specimens from the type locality in Honduras are mainly of historical significance.
Care and storage
## Cleaning Poughite is a very delicate mineral and potentially sensitive to water. For dust removal, only compressed air or a very soft, dry brush should be used. Any contact with water and cleaning solutions should be avoided. ## What to Avoid Water, ultrasonic cleaners, all chemicals, acids, and bases must be absolutely avoided. The mineral is soft and easily scratched. As a hydrated mineral, it is also sensitive to high temperatures, which can lead to its dehydration and destruction of its structure. It should be protected from moisture and direct sunlight. ## Storage Poughite specimens are best stored in stable, dry conditions. It is recommended to keep them in closed containers (e.g., "perky box" type) that protect against dust, moisture, and mechanical damage. Exposure should be away from heat sources and in lighting that does not emit a large amount of heat (e.g., LED).