Metaheimite
Chemical formula: Pb<sup>2+</sup>Cu<sup>2+</sup><sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)(OH)<sub>3</sub>
Metaheimeite is a rare lead and copper arsenate, forming small, tabular crystals of an intense green color.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous
- Streak
- Pale green
- Density
- 4.98
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of metaheimeite include its emerald-green color, the formation of small, tabular crystals often gathered in rosetted aggregates, and its occurrence in the oxidation zones of polymetallic deposits. Identification usually requires microscopic magnification. ## Distinguishing from Similar Minerals Metaheimeite can be confused with other secondary copper minerals, such as brochantite, malachite, agardite, or bayldonite. It differs from malachite by its crystal form (malachite rarely forms well-developed crystals, more often fibrous or botryoidal aggregates) and lack of reaction with hydrochloric acid. Distinguishing it from other green arsenates (like bayldonite) is very difficult visually and often requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms Crystals are very small, tabular or bladed, often with a hexagonal outline. They usually form radial or rosetted aggregates, as well as thin crusts and coatings.
Geological environment
## Genesis Metaheimeite is a secondary mineral, formed as a result of weathering and oxidation processes of primary ore minerals (sulfides) in polymetallic deposits. Its crystallization requires the presence of lead, copper, and arsenic in aqueous solutions under low temperature and pressure conditions, typical of the near-surface zone. ## Mineral Associations This mineral often co-occurs with other secondary minerals of the oxidation zone, such as bayldonite, duftite, mimetite, olivenite, azurite, malachite, cerussite, as well as quartz and iron oxides (goethite, hematite). ## Localities The most important and classic localities, from which well-formed specimens originate, are the Tsumeb mine in Namibia and mines in the Cornwall region of Great Britain. It also occurs in other places worldwide where suitable geochemical conditions exist, e.g., in Greece (Lavrion), Germany (Black Forest), and the USA (Arizona).
Rarity
Rare
For collectors
## Quality Criteria As a micromineral, the collector's value of metaheimeite is determined by the quality and form of the crystals visible under the microscope. Most prized are specimens with sharp, well-formed, individual crystals or aesthetic, rosetted aggregates of an intense, emerald-green color. The contrast with the matrix and the presence of rare associated minerals are also important. ## Popular Localities The most sought-after specimens by collectors come from the Tsumeb mine in Namibia, which is famous for its exceptional quality and diversity of secondary minerals. Historical specimens from Cornwall (Great Britain) are also highly valued.
Care and storage
## Cleaning Metaheimeite specimens are extremely delicate and should be cleaned with the utmost care. It is recommended to use only compressed air (from a safe distance) to remove dust. Avoid contact with water and any chemicals. Mechanical cleaning, even with a soft brush, can damage the tiny crystals. ## What to Avoid Avoid ultrasonic cleaners, all solvents, acids, and detergents. The mineral is sensitive to high temperatures and sudden temperature changes. The crystals are very brittle and susceptible to impacts and abrasions. ## Storage Metaheimeite specimens, as typical microminerals, should be stored in specialized, sealed boxes (so-called "micromount boxes") that protect them from dust and mechanical damage. Avoid exposure to direct sunlight.