Cualstibite

Chemical formula: Cu<sup>2+</sup><sub>2</sub>AlSb<sup>5+</sup>(OH)<sub>12</sub>

A rare copper-aluminum hydroxyantimonate, forming characteristic blue-green coatings and microcrystals.

## Characteristics Cualstibite is a rare secondary mineral from the hydroxide group, chemically classified as a copper-aluminum hydroxyantimonate. It occurs as very small, tabular or platy crystals with a hexagonal outline, rarely exceeding 0.5 mm. Most commonly, it forms rosette-like aggregates, spherical clusters, thin crusts, and coatings on rock surfaces. Its intense, blue-green color is very characteristic. ## Physical Properties Cualstibite crystals exhibit a vitreous luster. The mineral is translucent. Due to the small size of the crystals, hardness is difficult to determine precisely, but it is estimated to be around 2 on the Mohs scale. The calculated density is 3.43 g/cm³. ## Colors and Varieties Cualstibite occurs in a uniform, characteristic color, described as turquoise, bluish-blue, or blue-green. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition: "Cu" from copper (Latin: *cuprum*), "Al" from aluminum (*aluminium*), and "Stib" from antimony (*stibium*). It was first described in 1981 by P.J. Williams based on samples found in the Dome Rock Copper mine in Minginew Shire, Western Australia. This is its type locality. ## Uses Cualstibite has no industrial application. Its significance is purely scientific and collectible, being valued by collectors of rare minerals and micromounts.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Pale blue
Density
3.43
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Trigonal

Diagnostic features

## Identification Cualstibite is primarily identified based on its characteristic, intense blue-green color, its occurrence as small, rosette-like aggregates or coatings, and its specific geological environment – oxidation zones of copper and antimony ores. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals of similar color, such as turquoise, aurichalcite, cyanotrichite, or spangolite. It differs from turquoise by its significantly lower hardness and different crystal habit. From aurichalcite and cyanotrichite, it differs by its crystal habit (tabular, not acicular) and lack of reaction with acids. Spangolite forms more developed, pseudohexagonal crystals. ## Crystal Forms It forms very small, thin, tabular crystals with a hexagonal outline. These crystals often combine into rosette-like or fan-shaped aggregates. It also occurs as spherical clusters, crusts, and earthy coatings.

Geological environment

## Genesis Cualstibite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits containing copper and antimony. It forms under conditions of low temperatures and pressures, as a result of surface waters acting on primary minerals of these metals. ## Mineral Associations It most commonly co-occurs with other secondary minerals, such as malachite, azurite, chalcanthite, brochantite, antlerite, and also with antimony minerals, e.g., stibiconite and bindheimite. Quartz and clay minerals may also be associated with it. ## Localities The most important and well-known cualstibite localities worldwide include: - Australia: Dome Rock Copper mine in Western Australia (type locality). - USA: Cole mine and Bisbee mine in Cochise County, Arizona; Gold Hill mine in Tooele County, Utah. - Germany: Caspari mine in Uentrop, North Rhine-Westphalia.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, though still microscopic, crystals forming aesthetic, rosette-like aggregates are most valued by collectors. The intensity and purity of the blue-green color are crucial. Contrast with the rock matrix and the abundance of clusters on the specimen's surface are also important. Due to its microscopic nature, specimens are almost exclusively the domain of micromount collectors. ## Popular Localities Specimens from classic localities in Arizona (USA), especially from the Cole mine, which yield rich coatings of vibrant color, are considered the best. Specimens from the type locality in Australia are also sought after by specialists.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Contact with water is not recommended due to the mineral's delicacy and potential reactivity. Ultrasonic cleaners and any brushes should be avoided. ## What to Avoid Contact with acids and other chemicals, which can destroy the mineral, must be strictly avoided. It is very soft and brittle, so it must be protected from impacts and scratching. It should not be heated or exposed to prolonged moisture. ## Storage Cualstibite specimens, especially micromounts, are best stored in sealed, transparent boxes (so-called "membrane boxes" or micromount boxes) that protect them from dust, moisture, and mechanical damage. Exposure to strong light is not recommended.

Sources

Read more