Tsumebite
Chemical formula: Pb<sup>2+</sup><sub>2</sub>Cu<sup>2+</sup>(PO<sub>4</sub>)(S<sup>6+</sup>O<sub>4</sub>)(OH)
Tsumebite is a rare lead and copper phosphate and sulfate, forming characteristic emerald-green crystals, highly valued by collectors.
Properties
- Mohs hardness
- 3.5
- Luster
- Vitreous to Adamantine
- Streak
- Pale green
- Density
- 6.13
- Cleavage
- Good on {010}
- Fracture
- Conchoidal to uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Tsumebite is most easily recognized by its characteristic, intense emerald-green color, high luster, and form of small, tabular crystals. Its high density (specific gravity) is also an important indicator. Its occurrence in association with other secondary copper and lead minerals in oxidation zones is crucial for identification. ## Distinguishing from Similar Minerals Tsumebite is sometimes confused with other green secondary minerals. It is distinguished from malachite by its crystal form (malachite rarely forms distinct crystals, more often fibrous or botryoidal aggregates) and lack of reaction with hydrochloric acid. It differs from dioptase by its crystal form (dioptase forms trigonal prismatic crystals) and hardness (dioptase is harder). It is distinguished from brochantite by its brighter, more emerald color and different crystal form. ## Crystal Forms Tsumebite crystals are usually small, with tabular, wedge-shaped, or equant habits. They often form fan-like or rosette aggregates, as well as thin crusts on the host rock. Twinning is common, especially contact and penetration twins.
Geological environment
## Genesis Tsumebite is a secondary mineral, formed in the oxidation zones of hydrothermal polymetallic deposits rich in lead, copper, zinc, arsenic, and phosphorus. It crystallizes as a result of the weathering of primary sulfides (galena, chalcopyrite) and phosphates (apatite) in the presence of sulfate-rich waters. ## Mineral Associations This mineral often co-occurs with other secondary minerals of the oxidation zone. The most common associated minerals include: smithsonite, cerussite, malachite, azurite, wulfenite, mimetite, olivenite, anglesite, and duftite. ## Localities The most important and historical locality, from which the world's best tsumebite specimens originate, is the Tsumeb mine in Namibia. Other known, though much rarer, occurrences include Broken Hill in New South Wales (Australia), several locations in Arizona (USA), and the Laurion region in Greece.
Rarity
Rare
For collectors
## Quality Criteria The most highly prized tsumebite specimens are characterized by an intense, emerald-green color, high transparency, and strong luster. Crystal habit is also crucial – sharp, well-defined crystals are sought after, especially those forming aesthetic, rosette-like aggregates. Crystal size is important, although even small but perfectly formed specimens are highly valued. A contrasting matrix, such as white cerussite or smithsonite, enhances its attractiveness. ## Popular Localities The absolute classic and most desirable locality for tsumebite is the Tsumeb mine in Namibia. Specimens from this location are considered the unsurpassed standard for this mineral and fetch the highest prices in the collector's market.
Care and storage
## Cleaning Tsumebite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If wet cleaning is necessary, use distilled water and a very gentle brush, avoiding vigorous scrubbing. After cleaning, the specimen should be immediately and thoroughly dried. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral. Tsumebite is sensitive to high temperatures. Prolonged exposure to intense sunlight can cause color fading. ## Storage Tsumebite specimens, especially those with well-formed crystals, are fragile and should be stored in separate, padded boxes to prevent mechanical damage. They should be protected from dust, moisture, and sudden changes in temperature.