Lapeyreite
Chemical formula: Cu<sup>2+</sup><sub>3</sub>O[As<sup>5+</sup>O<sub>3</sub>(OH)]<sub>2</sub>·H<sub>2</sub>O
A very rare, secondary copper arsenate, forming characteristic, platy aggregates of olive-green color.
Properties
- Luster
- Vitreous to Pearly
- Streak
- Pale green
- Density
- 4.26
- Cleavage
- Perfect on {100}
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features include its olive-green color, unique form as spherical aggregates composed of flexible lamellae, and its origin from the type locality. Identification usually requires microscopic magnification. ## Distinguishing from Similar Minerals Lapeyreite can be confused with other secondary, green copper arsenates, such as geminite, lavendulan, or olivenite. However, it is distinguished by its characteristic, platy and flexible habit, whereas other minerals most often form acicular crystals, crusts, or fibrous forms. ## Crystal Forms It does not form well-developed, single crystals. It occurs exclusively as spherical or fan-shaped aggregates, which consist of sub-millimeter, thin, and flexible lamellae oriented radially from the center.
Geological environment
## Genesis It is a secondary mineral, forming in the oxidation zones of hydrothermal gold deposits that are rich in sulfides and arsenides. It forms as a result of the weathering of primary ore minerals in a copper and arsenic-rich environment. ## Mineral Associations It most often co-occurs with other rare, secondary arsenates. At the type locality, it was found in association with geminite, lavendulan, pharmacolite, arsenolite, and native arsenic. ## Localities The only confirmed and described occurrence in the world is the historic Salsigne gold mine, located near Carcassonne in the Aude department, France. This is the type locality for this mineral.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens by collectors are those that display well-formed, spherical aggregates of intense, olive-green color, clearly contrasting with the host rock. Due to its microscopic size, the value of a specimen is determined by its photogenicity and aesthetics under magnification. A complete, compact aggregate form is more important than its size. ## Popular Localities The only source of collector specimens is the Salsigne mine in France. Material from this locality is the absolute standard for the species, and every lapeyreite specimen on the market originates from there.
Care and storage
## Cleaning Dry cleaning is recommended, using a soft brush or non-contact cleaning with a photographic blower to remove dust. Contact with water, ultrasound, and any chemical agents must be strictly avoided. ## What to Avoid The mineral is sensitive to changes in temperature and humidity, which can lead to partial dehydration and alteration of properties. It should be protected from direct sunlight, high temperatures, and humidity. Due to its arsenic content, caution should be exercised during handling, and hands should be washed after each contact. ## Storage Lapeyreite specimens should be stored under stable room conditions, preferably in tightly sealed "micromount" boxes. This protects the delicate lamellae from mechanical damage, dust, and humidity fluctuations.