Clairite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>Fe<sup>3+</sup><sub>3</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>(OH)<sub>3</sub>·3H<sub>2</sub>O

Clairite is a very rare, hydrated ammonium iron sulfate, forming microscopic, yellowish-brown crystals in products of mine fires.

## Characteristics Clairite is a secondary mineral, occurring as very small, platy or acicular crystals, which rarely exceed 0.5 mm in length. It forms druses and coatings on rocks. Its crystals are transparent to translucent and exhibit a vitreous luster. ## Physical Properties Due to the microscopic size of the crystals, many physical properties, such as hardness or density, have not been precisely determined. The mineral is brittle. ## Colors and Varieties Clairite occurs in shades from yellow to yellowish-brown. No varieties have been distinguished. ## History and Name The mineral was named in honor of Claire Gerstmann (born 1949), an American micromineral collector and photographer, who first found this mineral. It was described and approved as a new mineral species in 1978 by Peacor, Dunn, and Simmons. ## Uses Clairite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and microminerals.

Properties

Luster
Vitreous
Streak
Light yellow
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Identification of clairite requires specialized equipment, usually a stereoscopic microscope. Identification is confirmed using advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. A characteristic feature is its occurrence in a specific environment (products of mine dump fires) and the typical form of small, platy crystals. ## Differentiation from similar minerals It can be confused with other secondary iron sulfates formed under similar conditions, such as jarosite or copiapite. Differentiation with the naked eye is practically impossible and requires chemical and crystallographic analysis. ## Crystal forms Clairite forms very small, elongated crystals with a platy or acicular habit. They usually occur in the form of radial aggregates, rosettes, or chaotic clusters and coatings.

Geological environment

## Genesis Clairite is a secondary mineral, formed as a result of fires in mine dumps (so-called fumarolic processes). It forms in lower temperature zones due to the reaction of gases released during coal combustion with clay and sulfide minerals present in the waste rock. ## Mineral associations It most often co-occurs with other rare secondary minerals formed in the same environment, such as boussingaultite, mascagnite, tschermigite, native sulfur, sal ammoniac, and lonsdaleite. ## Localities The type and best-known locality is the St. Claire coal mine in Schuylkill County, Pennsylvania, USA, where the mineral was discovered. Its occurrence has also been confirmed in several other places around the world with similar genesis, for example, in mine dumps in Kladno, Czech Republic.

Rarity

Very rare

For collectors

## Quality criteria Due to the microscopic nature of the mineral, its collector value primarily depends on the richness and aesthetics of crystal aggregates on the rock matrix. Specimens with clearly formed, undamaged crystals forming visually attractive aggregates, visible under a microscope, are most valued. The size of the crystals, although always small, is also important - larger needles are more desirable. ## Popular localities The only source of collector-grade specimens is the type locality - the St. Claire mine in Pennsylvania, USA.

Care and storage

## Cleaning Clairite specimens are extremely delicate and brittle. Any mechanical cleaning, including the use of brushes, should be avoided. Only careful dust removal with a photographic air blower is permissible. ## What to avoid The mineral is water-soluble, so contact with water and other liquids must be strictly avoided. It should be protected from moisture, high temperatures, and chemicals. ## Storage It is recommended to store specimens exclusively in sealed, closed "micromount" boxes to protect them from mechanical damage, dust, and humidity changes.

Sources

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