Juanitaite

Chemical formula: (Cu₂+,Ca,Fe₂+)₁₀Bi₃+(As₅+O₄)₄(OH)₁₁·₂H₂O

Juanitaite is a very rare, soft copper, bismuth, and calcium arsenate, forming small, platy crystals of a yellowish-green color.

## Characteristics Juanitaite is a very rare mineral from the arsenate group, chemically classified as a hydrated copper, bismuth, and calcium arsenate. It occurs as very small, thin, platy crystals, often forming rosetted or spherical aggregates. Typical specimens have an intense yellowish-green to olive-green color, and due to the small size of the crystals, they are best observed under magnification. ## Physical Properties This mineral is extremely soft, with a Mohs hardness of only 1, meaning it can be scratched with a fingernail. It has a resinous luster and is translucent. Its density is relatively high, approximately 3.61 g/cm³. ## Colors and Varieties Juanitaite occurs in characteristic shades of green, from yellowish-green to olive. No distinct color varieties or commercial varieties are recognized. ## History and Name Juanitaite was first described in 1971. Its name comes from Juanita, the wife of Eugene Cisneros, one of the mineral's discoverers. The type locality, from which the first described specimens originated, is the Gold Hill Mine in Tooele County, Utah, USA.

Properties

Mohs hardness: 1
Luster: Resinous
Streak: greenish yellow
Density: 3.61
Cleavage: perfect on {001} and {110}, and good on {100}
Fracture: None observed
Transparency: Translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Characteristic features of juanitaite include its extremely low hardness (1 on the Mohs scale), yellowish-green color, resinous luster, and occurrence in the form of small, platy crystals forming aggregates. A yellowish-green streak is also helpful for identification. ## Distinguishing from Similar Minerals It can be confused with other green secondary copper minerals, such as mixite or agardite. However, juanitaite is distinguished by its significantly lower hardness, specific crystal habit, and the presence of bismuth in its composition, which requires advanced analysis (e.g., EDS). ## Crystal Forms It forms very small, thin, square or rectangular crystals with a platy habit. These crystals often combine into rosetted, spherulitic, or radial aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis Juanitaite is a secondary mineral, forming in the oxidation zones (weathering) of ore deposits rich in copper, bismuth, and arsenic. It forms as a result of the alteration of primary minerals containing these elements. ## Mineral Associations At the type locality (Gold Hill, Utah), it co-occurs with minerals such as mixite, conichalcite, olivenite, malachite, azurite, barite, quartz, and iron oxides. ## Localities This is an extremely rare mineral, known from only a few localities worldwide. Besides the type locality at the Gold Hill Mine in Utah (USA), its occurrence has also been reported in the Clara Mine in the Black Forest (Germany) and in small quantities in several other locations in Europe and the USA.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, juanitaite is primarily valued for the quality and development of its microscopic crystals. The most desirable specimens are those with well-defined, sharp crystals forming aesthetic, rosetted aggregates. The intensity and purity of the yellowish-green color also contribute to the specimen's attractiveness. Contrast with the rock matrix can further enhance its visual appeal. ## Popular Localities The most classic and prized specimens come from the type locality – the Gold Hill Mine in Utah, USA. Specimens from the Clara Mine in Germany are also known and sought after by specialized collectors.

Care and storage

## Cleaning Due to its extreme softness (Mohs hardness of 1), mechanical cleaning is highly inadvisable. Dust can only be removed very carefully with a soft brush or a photographic air blower. Contact with water and any chemicals should be avoided. ## What to Avoid Juanitaite is an extremely delicate mineral. Avoid: - Touching with fingers – it can be damaged even by a fingernail. - All liquids, including water and alcohol. - Ultrasonic and steam cleaners. - Sudden temperature changes and direct sunlight. - Vibrations and shocks. ## Storage Juanitaite specimens should be stored exclusively in stable, sealed collector boxes (so-called "micromount boxes"), away from other minerals that could damage them. It should be protected from dust, light, and moisture.

External references

https://www.mindat.org/min-7123.html