Paramolybdomenite

Chemical formula: Pb₂+Se₄+O₃

Paramolybdomenite is a rare lead selenite, an orthorhombic dimorph of molybdomenite, forming small, colorless to pale yellow crystals.

## Characteristics Paramolybdomenite is a rare secondary mineral from the selenite group. It forms very small, thin, tabular or bladed crystals, rarely exceeding a few millimeters in length. They usually occur as small aggregates, coatings, or druses on the host rock. The mineral is characterized by a strong, adamantine or resinous luster, which is typical for minerals with high lead content. ## Physical Properties It is a very soft and brittle mineral. Its Mohs hardness is about 2.5-3. It has an exceptionally high density of approximately 6.46 g/cm³, which makes even small specimens surprisingly heavy. It is transparent to translucent. ## Colors and Varieties Paramolybdomenite is most often colorless, white, grayish, or pale yellow. It does not form color varieties or commercial varieties. ## History and Name The mineral was first described in 1953 by G.F. Claringbull. Its name comes from the Greek word *para* (παρά), meaning "beside" or "near", and the name of the mineral molybdomenite. This name refers to the fact that paramolybdomenite is a dimorph of molybdomenite – both minerals have the same chemical formula (PbSeO₃) but crystallize in different crystallographic systems (paramolybdomenite in orthorhombic, and molybdomenite in monoclinic). ## Uses Due to its rarity and small crystal size, paramolybdomenite has no industrial application. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 2.5-3
Luster: Adamantine to resinous
Streak: White
Density: 6.46
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification The most important diagnostic feature of paramolybdomenite is its very high density, unusual for a mineral with a non-metallic appearance. A strong, adamantine luster is also characteristic. Certain identification is mainly possible based on chemical and X-ray diffraction (XRD) analysis, which will confirm the composition and crystal structure. ## Distinguishing from similar minerals Paramolybdomenite is visually indistinguishable from its dimorph, molybdomenite, without advanced studies. It can be confused with other secondary lead minerals, such as cerussite (PbCO₃) or anglesite (PbSO₄). However, it differs from them in its environment of occurrence (association with other selenites) and usually smaller crystal sizes. Wulfenite (PbMoO₄) usually has more intense colors (yellow, orange) and a different crystal form. ## Crystal forms Crystals are usually very small, thin-tabular, bladed, or acicular. They often form radial aggregates, rosettes, or thin coatings and crusts on rock surfaces.

Geological environment

## Genesis Paramolybdomenite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in selenium and lead. It forms as a result of the alteration of primary selenium minerals and lead sulfides under low temperature and pressure conditions. ## Mineral associations It most often co-occurs with other rare selenites and selenates, such as molybdomenite, olsacherite, chalcomenite, as well as with more common secondary minerals like cerussite and anglesite. ## Localities The type locality is Cerro de Cacheuta in Mendoza Province, Argentina. Other known occurrences include the Tsumeb mine in Namibia, the Pacajake deposit in Bolivia, and the Organ Mountains region in New Mexico, USA.

Rarity

Very rare

For collectors

## Quality criteria Specimens with well-formed, sharp, and transparent crystals are most valued by collectors, even if they are small. Rich crystal aggregates on a contrasting rock matrix are highly prized. The value of a specimen significantly increases if it occurs in association with other rare selenite minerals. ## Popular localities Specimens from the type locality in Argentina and from the Tsumeb mine in Namibia, which was famous for its exceptional secondary minerals, are considered the best in the world. However, specimens from these locations are historical and very difficult to acquire.

Care and storage

## Cleaning Paramolybdomenite specimens are very delicate and brittle. For dusting, it is best to use a soft, dry brush. Wet cleaning should be avoided; if absolutely necessary, a small amount of distilled water can be used, and the specimen should be thoroughly dried immediately. ## What to avoid The mineral is sensitive to acids and other chemicals. Ultrasonic cleaners or steam cleaning should not be used. As a lead-containing mineral, it is potentially toxic – hands should be washed after each contact with the specimen. Inhaling dust should be avoided. ## Storage It is recommended to store specimens in closed, padded boxes or display cases to protect them from mechanical damage and dust. Exposure to extreme temperatures and humidity should be avoided. Tweezers are best used when handling.

Sources

IMA Mineral List (CNMNC)