Raisaite

Chemical formula: Cu<sup>2+</sup>Mg[Te<sup>6+</sup>O<sub>4</sub>(OH)<sub>2</sub>]·6H<sub>2</sub>O

Raisaite is a very rare, blue copper, magnesium, and tellurium mineral, forming acicular crystals in Californian gold deposits.

## Characteristics Raisaite is a hydrated copper and magnesium tellurate. It occurs as small, radial aggregates or acicular and bladed crystals. Its characteristic feature is an intense, bright blue to bluish-green color, which distinguishes it from the host rock. ## Physical Properties Raisaite crystals are transparent to translucent and exhibit a vitreous luster. It is a soft mineral, with a Mohs hardness of approximately 2-3. Its density is low, estimated at about 2.66 g/cm³. ## Colors and Varieties This mineral does not form color varieties. Its color is stable and ranges from light blue to greenish-blue hues, depending on subtle differences in chemical composition and crystallization conditions. ## History and Name Raisaite was first described in 2000 by G.E. Dunning and co-workers. Its name honors Raisa I. Organova (born 1930), a Russian crystallographer specializing in the study of tellurium minerals. ## Applications Due to its extreme rarity and occurrence as microscopic crystals, raisaite has no industrial applications. It is solely an object of interest for collectors and scientists.

Properties

Mohs hardness
2-3
Luster
Vitreous
Streak
Light blue
Density
2.66
Cleavage
Perfect on {010}
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Raisaite is identified by its characteristic light blue color, acicular crystal habit forming radial aggregates, and its occurrence in paragenesis with other rare tellurates. ## Differentiation from Similar Minerals It can be confused with other blue secondary copper minerals, such as chalcanthite, linarite, or azurite. However, it is distinguished by its specific geological environment (tellurium deposits) and co-occurrence with other tellurates. Final identification requires advanced analytical methods, such as XRD or EDS. ## Crystal Forms It forms slender, acicular or bladed crystals, often grouped into radial, stellate, or chaotic aggregates. Single, well-formed crystals are extremely rare.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones of hydrothermal gold and tellurium deposits. It crystallizes as a result of the weathering of primary tellurides in the presence of solutions rich in copper and magnesium. ## Mineral Associations It co-occurs with other rare tellurium minerals, such as quetzalcoatlite, dugganite, frankhawthorneite, ottoite, as well as native gold, quartz, and manganese minerals. ## Localities The main and best-known occurrence is the type locality - the Otto Mountain mine in San Bernardino County, California, USA. This is one of only a few confirmed localities for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those with rich, dense aggregates of intensely blue crystals, contrasting with the rock matrix. The presence of other well-formed associated minerals, especially gold, is also important. ## Popular Localities Almost all collectible specimens come from a single location - the Otto Mountain mine in California. This locality is known worldwide for providing the best specimens of raisaite and other rare tellurates.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Any contact with water or chemicals is highly risky. ## What to Avoid Avoid ultrasonic cleaners, all chemical solvents, acids, and detergents. The mineral is very soft and brittle, susceptible to mechanical damage. It should be protected from high temperatures and direct sunlight, which can cause dehydration and color change. ## Storage It is recommended to store specimens in specialized "micromount" boxes, protecting them from dust, shocks, and sudden changes in humidity.

Sources

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