Faustite

Chemical formula: Zn<sup>2+</sup>Al<sub>6</sub>(PO<sub>4</sub>)<sub>4</sub>(OH)<sub>8</sub>·4H<sub>2</sub>O

Faustite is a rare hydrated zinc and aluminum phosphate, a zinc analogue of turquoise, valued for its characteristic apple-green coloration.

## Characteristics Faustite is a mineral from the turquoise group, in which zinc predominates over copper. It usually occurs in the form of microcrystalline aggregates, earthy masses, crusts, or as fillings of small veins. It rarely forms small, hemispherical aggregates with a radial structure. Its appearance is very similar to turquoise, but it is distinguished by a characteristic apple-green or greenish-blue hue, often lighter than typical turquoises. ## Physical Properties This mineral is characterized by a hardness of about 4.5 on the Mohs scale, making it relatively soft. Its luster is waxy to earthy, and in compact masses, it can be dull. It is an opaque mineral. The density of faustite is approximately 2.92 g/cm³. ## Colors and Varieties Faustite most often exhibits colors ranging from apple-green and yellowish-green to greenish-blue. The color depends on the zinc-to-copper ratio in its structure – a higher zinc content favors green hues. No distinct commercial varieties are distinguished, and its name is directly related to its chemical composition. ## History and Name The mineral's name honors Dr. George Tobias Faust (1908-1985), an American mineralogist and geologist who worked for the U.S. Geological Survey. Faustite was first described in 1953 based on material found in the Copper King mine in Eureka County, Nevada, USA. ## Uses Due to its rarity, faustite is primarily a mineral of collector's interest. It is sometimes used as an ornamental stone, similar to turquoise, but its lower hardness and rarity limit such use.

Properties

Mohs hardness
4.5
Luster
Waxy to earthy
Streak
White to greenish
Density
2.92
Cleavage
Perfect on {001} and good on {010}
Fracture
Conchoidal to granular
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification The key diagnostic feature of faustite is its apple-green color, distinguishing it from the usually bluer turquoise. It occurs as microcrystalline masses, crusts, and veins. However, final confirmation requires chemical analysis to ascertain the dominance of zinc over copper. ## Distinguishing from Similar Minerals Faustite is most often confused with turquoise, of which it is a zinc analogue. It differs mainly in color (more green) and slightly lower hardness. It can also be similar to variscite, which, however, usually has a different shade of green and does not contain copper or zinc. It is distinguished from chrysocolla by its higher hardness. ## Crystal Forms Well-formed crystals are extremely rare. Faustite primarily forms compact, massive, earthy aggregates, as well as spherical and reniform aggregates with a radial structure. It often occurs as thin veins and crusts on the host rock.

Geological environment

## Genesis Faustite is a secondary mineral, forming in the oxidation zones of ore deposits, in sedimentary or volcanic rocks rich in aluminum and phosphorus. Its formation is associated with low-temperature hydrothermal solutions that supply zinc. It forms under arid and semi-arid conditions. ## Mineral Associations This mineral often co-occurs with turquoise, variscite, quartz, kaolinite, montmorillonite, as well as minerals from the alunite-jarosite group. At its discovery site (Nevada, USA), it was accompanied by pyrite, chalcopyrite, and sphalerite in the host rock. ## Localities The most important and type locality for faustite is the Copper King mine in Eureka County, Nevada, USA. It is also known from several other localities worldwide, including the Shanshan mine in Hami Prefecture (Xinjiang, China) and the Bisbee mine in Arizona, USA. Occurrences have also been reported in Germany and Brazil.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with an intense, uniform, apple-green color. Well-formed spherical aggregates or veins with a distinct color, contrasting with the host rock, enhance attractiveness. The purity of the material and the absence of brown or black inclusions of iron and manganese oxides also affect its value. ## Popular Localities Classic and most sought-after faustite specimens come from the type locality – the Copper King mine in Nevada. Material from this mine is considered exemplary for this mineral. Specimens from China also appear on the collector's market.

Care and storage

## Cleaning Faustite specimens should be cleaned very carefully, using only a soft, dry brush to remove dust. If necessary, a slightly dampened (with distilled water) soft cloth can be used, immediately drying the specimen. Ultrasonic and steam cleaners should be avoided. ## What to Avoid Faustite is a porous and chemically sensitive mineral. Contact with acids, detergents, perfumes, cosmetics, and oils, which can permanently alter its color, must be strictly avoided. It is also sensitive to high temperatures and prolonged exposure to intense sunlight, which can lead to dehydration and fading. ## Storage Faustite specimens are best stored in separate, padded boxes or bags to prevent scratching by harder minerals. They should be protected from moisture, sudden temperature changes, and direct sunlight.

External references

Sources

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