Feinglosite

Chemical formula: Pb²⁺₂Zn²⁺(As⁵⁺O₄)₂·H₂O

Feinglosite is a rare, hydrated lead and zinc arsenate with a characteristic pale olive-green color, found in the Tsumeb mine in Namibia.

## Characteristics Feinglosite is a rare secondary mineral from the brackebuschite supergroup, being a hydrated lead and zinc arsenate. It forms very small, bladed or tabular crystals, which usually occur as radial aggregates or rosettes. Its characteristic features are a pale olive-green color and a strong, almost adamantine luster. ## Physical Properties Feinglosite crystals are translucent and exhibit a hardness of 4-5 on the Mohs scale. The luster is strongly vitreous to adamantine. The streak is white. It is a relatively heavy mineral due to its high lead content. ## Colors and Varieties This mineral occurs in a uniform, pale olive-green color. No color or commercial varieties have been distinguished. ## History and Name Feinglosite was first described in 1998. Its name honors Murray Feinglos (born 1948), an American physician and mineral collector who specialized in Tsumeb minerals and was the first to notice this mineral. The type locality is the famous Tsumeb mine in Namibia. ## Uses Feinglosite has no industrial application. It is solely an object of interest for specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
4-5
Luster
Adamantine
Streak
White
Density
0
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Feinglosite can be identified by its characteristic pale olive-green color, adamantine luster, and mode of occurrence – small, radial aggregates of bladed crystals. Its association with other rare arsenates from Tsumeb is also crucial. ## Distinguishing from similar minerals It can be confused with other green arsenates from the brackebuschite group, such as arsenbrackebuschite or tsumcorite. Final differentiation requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal forms Crystals are very small, elongated and flattened (bladed), often forming fan-shaped or radial aggregates and rosettes. They rarely occur as single, well-formed crystals.

Geological environment

## Genesis Feinglosite is a secondary mineral that forms in the oxidation zones (gossans) of polymetallic deposits rich in lead, zinc, and arsenic. It forms as a result of the weathering of primary sulfides, such as galena, sphalerite, and tennantite. ## Mineral associations This mineral coexists with other rare secondary minerals, especially arsenates. At the type locality (Tsumeb), it was found in association with quartz, willemite, tsumcorite, ludlockite, leiteite, and schneiderhöhnite. ## Localities The only confirmed and described locality for feinglosite in the world is the Tsumeb mine (Ongopolo Mine) in the Oshikoto Region, Namibia. This is its type locality.

Rarity

Very rare

For collectors

## Quality criteria The most prized specimens are those with clearly formed, radial aggregates of crystals, set on a contrasting rock matrix. Due to the microscopic size of the crystals, the aesthetics of the entire cluster and the absence of damage are crucial. The color, although uniform, should be as vibrant as possible. ## Popular localities The only source of feinglosite specimens is the Tsumeb mine in Namibia. All specimens available on the collector's market come from this single, historical locality.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to potential solubility and fragility, contact with water and any chemical agents should be avoided. ## What to avoid Contact with water, acids, detergents, and ultrasonic cleaners, which can damage or destroy delicate crystals, must be strictly avoided. The mineral is brittle and sensitive to impacts and scratches. ## Storage It is recommended to store specimens in stable conditions, away from moisture and dust, preferably in a sealed "micromount" box. Avoid exposure to direct sunlight and sudden temperature changes.

External references

Sources

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