Zincrosasite
Chemical formula: (Zn²⁺,Cu²⁺)₂(CO₃)(OH)₂
Zincrosasite is the zinc analog of rosasite, forming characteristic spherical aggregates of an intensely blue or greenish-blue color.
Properties
- Mohs hardness
- 1
- Color
- White, light blue
- Luster
- Silky
- Streak
- pale blue
- Density
- 0
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification A characteristic feature of zincrosasite is its spherical, radially fibrous aggregates of blue or greenish-blue color. It reacts vigorously with hydrochloric acid, which is typical for carbonates. It often forms thin crusts on host rocks. ## Distinguishing from Similar Minerals Zincrosasite is difficult to distinguish from rosasite without chemical analysis; rosasite usually has a bluer hue due to a higher copper content. It can be confused with aurichalcite, which has similar forms and color, but is harder and has a different shade (usually more sky-blue). Distinguishing it from smithsonite or hemimorphite is possible based on its mode of occurrence – zincrosasite forms fibrous aggregates, not botryoidal or distinctly crystalline ones. ## Crystal Forms Crystals are very fine, acicular or hair-like. They almost always occur in the form of spherical or hemispherical aggregates with a radial internal structure. It also forms thin coatings and crusts.
Geological environment
## Genesis Zincrosasite is a secondary mineral, forming in the oxidation (weathering) zones of zinc and copper ore deposits. It crystallizes from aqueous solutions under conditions of low temperatures and pressures, most often in cavities and fissures of carbonate rocks (limestones, dolomites) or within zinc-lead ores. ## Mineral Associations It often co-occurs with other secondary minerals of the oxidation zone, such as: smithsonite, hemimorphite, aurichalcite, cerussite, malachite, azurite, as well as with primary sulfides like sphalerite and galena. ## Localities The most important and classic localities for this mineral are the Ojuela Mine in Mapimí (Durango, Mexico) and the Tsumeb Mine in Namibia. It also occurs in the Laurion area in Greece, in mines in Sardinia (Italy), and in several locations in the USA (e.g., Arizona and Utah).
Rarity
Rare
For collectors
## Quality Criteria The most prized zincrosasite specimens are characterized by an intense, uniform color (blue preferred) and well-formed, undamaged spherical aggregates. Specimens where the spherulites are clearly separated and deposited on a contrasting substrate (rock matrix) are highly valued. Associations with other rare secondary minerals, e.g., from the Tsumeb mine, also significantly increase collectible value. ## Popular Localities Specimens from the Ojuela Mine in Mexico and Tsumeb in Namibia are considered world-class and fetch the highest prices on the collector's market. Samples from Laurion in Greece are also valued.
Care and storage
## Cleaning Zincrosasite specimens are delicate and should be cleaned with great care. It is best to use a soft brush to remove dust. If necessary, the specimen can be very carefully rinsed in distilled water and then immediately dried. Ultrasonic cleaners should be avoided. ## What to Avoid As a carbonate, zincrosasite is sensitive to acids, which cause its vigorous dissolution (effervescence). Contact with any household chemicals should be avoided. Brittle, fibrous aggregates are susceptible to mechanical damage. ## Storage Specimens should be stored in separate, padded boxes to prevent abrasion and crumbling of delicate aggregates. They should be protected from dust and moisture. It is not sensitive to sunlight.