Otavite

Chemical formula: Cd<sup>2+</sup>CO<sub>3</sub>

A rare cadmium carbonate of the calcite group, most often forming small, rhombohedral crystals and crusty coatings with a pearly or vitreous luster.

## Characteristics Otavite is a rare mineral from the carbonate group, chemically cadmium carbonate (CdCO₃). It belongs to the calcite group, with which it shares a similar crystal structure. It most often occurs as small, rhombohedral or scalenohedral crystals, rarely exceeding a few millimeters in size. It also forms aggregates in the form of crusts, coatings, and granular masses, often on a substrate of other minerals, such as smithsonite or hemimorphite. ## Physical Properties Otavite is characterized by a Mohs hardness of 3.5 to 4. Its density is relatively high, approximately 5.03 g/cm³. This mineral exhibits perfect cleavage in three directions, parallel to the rhombohedron, which is typical for minerals of the calcite group. The luster of otavite is usually pearly on cleavage surfaces or vitreous to adamantine on crystal faces. ## Colors and Varieties Pure otavite is colorless or white. However, it is usually colored yellowish, reddish-brown, pink, or greenish due to admixtures and impurities. No named varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – it was first described in 1906 by Otto Schneider based on specimens found in the Tsumeb mine, in the Otavi Mountains in Namibia. The name directly refers to this geographical region. ## Uses Due to its rarity, otavite has no industrial significance. However, it is a highly valued and sought-after collector's mineral.

Properties

Mohs hardness
3.5-4
Luster
Vitreous, Adamantine, Pearly
Streak
White
Density
5.03
Cleavage
Perfect on {1011}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification A key diagnostic feature of otavite is its violent reaction with acids (e.g., cold, dilute hydrochloric acid), which is typical for carbonates. High density, rhombohedral cleavage, and co-occurrence with other minerals from the oxidation zone of zinc and lead deposits (like smithsonite) are also important indicators. The luster is often characteristically pearly. ## Distinguishing from Similar Minerals Otavite can be confused with other carbonates of the calcite group, such as calcite, smithsonite, or rhodochrosite. It is distinguished from calcite by its significantly higher density. From smithsonite (zinc carbonate), it can be difficult to distinguish without chemical analysis, although smithsonite more often forms botryoidal and reniform aggregates. Pink otavite may resemble rhodochrosite, but the latter usually has a more intense color and often occurs in different mineral associations. ## Crystal Forms Otavite crystallizes in the trigonal system. It most often forms small, well-formed rhombohedra and scalenohedra. Its aggregates in the form of thin crusts and coatings on other minerals, as well as granular or radial aggregates, are also common.

Geological environment

## Genesis Otavite is a secondary mineral formed in the oxidation (weathering) zones of hydrothermal ore deposits that are rich in cadmium. It forms as a result of the weathering of primary cadmium-bearing minerals, such as greenockite (cadmium sulfide), in the presence of carbonate-rich solutions. ## Mineral Associations This mineral often co-occurs with other secondary minerals of the oxidation zone, such as smithsonite, cerussite, hemimorphite, hydrocerussite, azurite, malachite, and greenockite. ## Localities The most important and classic locality for otavite is the Tsumeb mine in Namibia, from which the world's best specimens originate. Significant finds also come from the Montevecchio mine in Sardinia (Italy). Other documented localities include the Shangani mine in Zimbabwe, Broken Hill in New South Wales (Australia), as well as some sites in China (Yunnan province) and Vietnam.

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with well-formed, sharp crystals with a distinct luster. Color is also important – specimens with pink or reddish coloration are attractive. Crystal size is of great significance, as most are very small; specimens with crystals exceeding a few millimeters are rare. A contrasting rock matrix, such as dark tennantite, adds to its attractiveness. ## Popular Localities Undoubtedly, the most sought-after and highly valued otavite specimens come from its type locality – the Tsumeb mine in Namibia. Specimens from this location, especially historical ones, fetch the highest prices and are considered mineralogical classics.

Care and storage

## Cleaning Otavite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its reactivity with acids, no acidic cleaning agents should be used. ## What to Avoid Otavite is sensitive to acids – even weak ones, such as vinegar, cause it to effervesce violently and decompose. It must be protected from all chemicals, including household cleaning products. Also avoid ultrasonic cleaners and steam cleaning, which can damage delicate crystals and aggregates. ## Storage Specimens should be stored in separate, padded boxes to prevent scratching by harder minerals. It is a brittle mineral, so it requires protection from impacts and falls. It is best displayed in closed showcases, protected from dust and contaminants.

External references

Sources

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