Copper-bearing Austinite

Chemical formula: Ca(Zn,Cu)(AsO₄)(OH)

A copper-bearing variety of austinite, a zinc and calcium arsenate, forming characteristic acicular crystals with a color ranging from green to blue-green.

## Characteristics Cuproaustinite is a copper-bearing variety of austinite, in which copper ions partially substitute for zinc in the crystal structure. This mineral most often forms small, acicular or prismatic crystals, which frequently arrange themselves into radial aggregates, rosettes, or spherical clusters. It also occurs as crusts and coatings with a druzy texture. Its most characteristic feature is its color, directly related to its copper content. ## Physical Properties The hardness of this variety is similar to pure austinite, ranging from 4 to 4.5 on the Mohs scale, making it a relatively soft mineral. The luster is most often vitreous, and on the surfaces of aggregates, it can be silky. Crystals can be transparent to translucent. The density ranges from 4.13 to 4.16 g/cm³. ## Colors and Varieties The color of cuproaustinite is its main distinguishing feature and depends on the copper-to-zinc ratio. The spectrum of colors includes shades from pale green, through apple green, to intense blue-green. The name "cuproaustinite" is a varietal term, not the name of a distinct mineral species. This mineral forms a continuous solid solution with conichalcite, which is its end-member, purely copper equivalent. ## History and Name The name "austinite" honors American mineralogist Austin F. Rogers (1877-1957). The prefix "cupro-" (from Latin *cuprum* - copper) indicates the presence of this element in its chemical composition. This variety was first described based on specimens from the Gold Hill Mine in Tooele County, Utah, USA. ## Uses Cuproaustinite has no industrial applications. However, it is a valued and sought-after collector's mineral due to the attractive forms and colors of its crystals.

Properties

Mohs hardness: 4-4.5
Luster: Vitreous to silky
Streak: White to pale green
Density: 4.13-4.16
Cleavage: Good on {001} and {010}
Fracture: Uneven to conchoidal
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Key diagnostic features include its green to blue-green color, acicular crystal habit forming radial or spherical aggregates, and its occurrence in paragenesis with other secondary minerals of the oxidation zone, especially arsenates. ## Distinguishing from Similar Minerals Cuproaustinite is most often confused with conichalcite (CaCu(AsO₄)(OH)). These minerals form a continuous solid solution and often co-occur. Definitive distinction requires chemical analysis (e.g., EDS), as their physical properties are almost identical. Typically, conichalcite has a more grass-green color, while cuproaustinite can be lighter or have a bluish tint, though this is not a rule. It is distinguished from cuprian adamite by the lack of fluorescence under UV light. It is distinguished from malachite by the lack of reaction (effervescence) with hydrochloric acid. ## Crystal Forms The most common forms are aggregates of acicular, elongated crystals that form fan-shaped, radial, or spherical aggregates. It also occurs as fine-grained crusts covering the host rock (matrix).

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation zones (iron caps) of polymetallic ore deposits. It forms as a result of the weathering of primary minerals containing arsenic, zinc, and copper, such as sphalerite, tennantite, or enargite, in the presence of calcium-rich rocks. ## Mineral Associations It often co-occurs with other minerals of the oxidation zone, such as adamite (including its cuprian variety), conichalcite, olivenite, azurite, malachite, limonite, quartz, and calcite. ## Localities Among the most important and well-known localities for this variety are: - Gold Hill Mine, Tooele, Utah, USA - the type locality. - Tsumeb Mine, Namibia - known for the exceptional quality of many rare mineral specimens. - Ojuela Mine, Mapimí, Durango, Mexico - a classic locality for zinc and copper arsenates. - Kintore Mine, Broken Hill, New South Wales, Australia.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are characterized by an intense, blue-green color, well-formed, lustrous crystals forming aesthetic, spherical or radial aggregates. The size of the clusters, their abundance on the rock matrix, and the absence of damage are also important. Contrasting combinations with other minerals, such as white calcite, significantly increase the attractiveness of the specimen. ## Popular Localities Specimens from the Tsumeb Mine in Namibia and the Ojuela Mine in Mexico are considered world-class and fetch the highest prices on the collector's market. Specimens from the type locality in Gold Hill, Utah, are also sought after by collectors specializing in systematic minerals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water. Ultrasonic cleaners should be avoided, as they can damage delicate crystal aggregates. ## What to Avoid The mineral is sensitive to acids and strong chemicals. Due to its relatively low hardness, it is susceptible to scratching. As an arsenate, it is toxic if ingested or if dust is inhaled – hands should be washed after each contact with a specimen. Heating should be avoided. ## Storage It is recommended to store specimens in closed boxes or display cases to protect them from dust and mechanical damage. Exposure to moisture and direct sunlight should be avoided.

Sources

IMA Mineral List (CNMNC)