Molybdomenite

Chemical formula: Pb²⁺Se⁴⁺O₃

Molibdomenite is a rare lead selenite, forming colorless to white, tabular crystals with a pearly or vitreous luster.

## Characteristics Molibdomenite is a lead selenite, belonging to rare minerals. It occurs as small, flattened or tabular crystals, often forming rosette-like or fan-shaped aggregates. It can also be found in the form of lamellar and scaly masses. It is a brittle mineral, and its crystals rarely exceed a few millimeters in length. ## Physical Properties Molibdomenite crystals exhibit a hardness ranging from 2.5-3.5 on the Mohs scale. They have a pearly luster on cleavage surfaces and a vitreous luster on other faces. They are transparent to translucent. The mineral's density is high, approximately 6.95 g/cm³. ## Colors and Varieties Molibdomenite is typically colorless or white, sometimes with a yellowish or grayish tint. No colored or commercial varieties are distinguished. ## History and Name The mineral's name comes from the Greek words *molybdos* (μόλυβδος) meaning "lead" and *mene* meaning "moon," in reference to its lead and selenium content (selenium named after the Greek moon goddess Selene). The mineral was first described in 1877 by Antoine François Alfred Lacroix based on samples from Cerro de Cacheuta in Argentina. ## Uses Molibdomenite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals.

Properties

Mohs hardness
3.5
Color
Colorless to white, yellowish white.
Luster
Pearly, Vitreous
Streak
White
Density
7.07
Cleavage
On {001} and {h0l}, good.
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Molibdomenite can be identified by its characteristic white or colorless, tabular crystals with a pearly luster, high density, and occurrence in the oxidation zones of selenium deposits. It is very soft and has perfect cleavage in one direction. ## Distinguishing from Similar Minerals It can be confused with other secondary lead minerals, such as cerussite or anglesite. It is distinguished from them by its lower hardness, perfect cleavage, pearly luster, and chemical tests for the presence of selenium. Unlike cerussite, it does not react with hydrochloric acid. ## Crystal Forms It forms thin, tabular crystals with a hexagonal or octagonal outline. Crystals often arrange into fan-shaped, radial, or rosette-like aggregates. It also occurs as lamellar and scaly masses.

Geological environment

## Genesis It is a secondary mineral formed in the oxidation (weathering) zones of ore deposits containing selenium, mainly in paragenesis with other selenites and selenates. It forms under low-temperature conditions as a result of the oxidation of primary minerals, such as clausthalite (PbSe). ## Mineral Associations It most commonly co-occurs with other rare selenites, such as chalcomenite, cobaltomenite, and ahlfeldite. It is also accompanied by ore minerals like clausthalite, as well as malachite, azurite, and clay minerals. ## Localities The most important localities worldwide include the discovery site in Cerro de Cacheuta in Mendoza Province (Argentina) and the Tsumeb mine (Namibia). It also occurs in Bolivia (El Dragón mine), USA (Eagle mine, Colorado), as well as in Germany (Harz Mountains) and the Czech Republic (Příbram).

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals forming aesthetic, rosette-like or fan-shaped aggregates are most valued by collectors. The size of the crystals, their transparency, and contrast with the rock matrix are also important. Specimens from classic localities, such as Argentina or Bolivia, are particularly sought after. ## Popular Localities The most famous specimens, considered the best in the world, come from the El Dragón mine in the Potosí Department, Bolivia, where large, well-formed aggregates were found. Specimens from Cerro de Cacheuta in Argentina are also historically important.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to its softness and perfect cleavage, avoid washing with water and mechanical cleaning. ## What to Avoid Avoid contact with water, acids, and other chemicals. The mineral is very soft and brittle, susceptible to scratches and mechanical damage. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in stable conditions, in closed collector's boxes, away from dust, humidity, and direct sunlight. It should be isolated from harder minerals to prevent scratching.

External references

Sources

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