Calciopetersite

Chemical formula: Cu²⁺₆Ca(PO₄)₂(PO₃OH)(OH)₆·3H₂O

Calciopetersite is a rare secondary mineral from the mixite group, forming blue-green, acicular crystals and radial aggregates.

## Characteristics Calciopetersite is a hydrated copper and calcium phosphate, belonging to the mixite group. It occurs as fine, acicular or capillary crystals, which often form radial, spherical aggregates or crusts. Its structure is delicate, and individual crystals rarely exceed a few millimeters in length, giving specimens a characteristic fibrous appearance. ## Physical Properties Calciopetersite crystals exhibit a vitreous luster. Due to their small size and acicular form, hardness is difficult to measure precisely but is estimated to be around 3 on the Mohs scale. It is a relatively light mineral, with a density of approximately 3.25 g/cm³. ## Colors and Varieties This mineral is characterized by a vibrant, blue-green or turquoise color. No distinct varieties have been identified. ## History and Name Calciopetersite was first described in 1983 by Japanese mineralogists (Matsubara, Kato, Tiba, Saito). Its name refers to its chemical composition – the presence of calcium (Latin: *calcius*) – and its structural relationship to petersite, another mineral from the same group. The name petersite, in turn, honors Thomas A. Peters (1948–), curator of mineral collections at the Paterson Museum in New Jersey, USA. ## Uses Calciopetersite has no industrial applications. It is solely a mineral of scientific and collectible interest.

Properties

Mohs hardness
3
Color
Olive green
Luster
Vitreous
Streak
Light olive green
Density
0
Cleavage
None
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Characteristic features of calciopetersite include its blue-green color, acicular crystal habit, and the formation of radial aggregates. Its occurrence in the oxidation zones of copper deposits is also an important indicator. ## Distinguishing from Similar Minerals Calciopetersite is visually almost impossible to distinguish from other minerals of the mixite group, such as mixite itself, agardite, or petersite-(Y). Positive identification requires advanced chemical analyses (e.g., EDS) or X-ray diffraction (XRD). It can also be confused with other secondary copper minerals of similar color and form, such as chalcanthite (which is water-soluble) or tyrolite. ## Crystal Forms Crystals are very fine, elongated, acicular, or capillary. They typically occur as radial or stellate aggregates, as well as fibrous crusts on the host rock.

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal polymetallic deposits rich in copper. It forms as a result of reactions between phosphate-bearing solutions and primary copper minerals. ## Mineral Associations It often co-occurs with other secondary copper minerals and phosphates, such as pseudomalachite, libethenite, pyromorphite, as well as with quartz and goethite. ## Localities The most important localities yielding well-formed specimens are the Tsumeb mine in Namibia and the Majuba Hill mine in Pershing County, Nevada, USA. The mineral has also been identified in Japan (Hisanichi mine, Akita Prefecture - type locality) and in several places in Europe, e.g., in Germany (Sauerland).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens are those with well-defined, radial aggregates of intense, blue-green color, contrasting with the host rock. The size of the aggregates and the absence of damage to the delicate needles are also important. Due to the microscopic size of the crystals, specimens are most often intended for "micromount" collections. ## Popular Localities Specimens from the Tsumeb mine in Namibia are considered the best in the world, distinguished by the size and quality of their crystals. Finds from the Majuba Hill mine in Nevada, USA, are also highly valued.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Contact with water is not recommended due to the risk of damaging delicate crystals and potential solubility. ## What to Avoid Avoid all chemicals, including acids and detergents. The mineral is sensitive to ultrasound, high temperatures, and vibrations. Fragile needles can be destroyed even by touch. ## Storage It is recommended to store specimens in closed, padded "micromount" boxes to protect them from dust, mechanical damage, and sudden changes in humidity.

External references

Sources

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