Definition
Conichalcite is a secondary arsenate mineral composed of calcium, copper, arsenic, oxygen, and hydrogen, with the ideal chemical formula CaCu(AsO₄)(OH). It is classified within the arsenate mineral group.
Overview
Conichalcite commonly occurs as a product of the oxidation and weathering of primary arsenic‑bearing sulfide minerals in hydrothermal veins and supergene environments. It is typically found in the oxidized zones of copper–arsenic ore deposits and can be associated with minerals such as linarite, olivenite, azurite, and malachite. Deposits are reported from localities in Europe, North America, and Australia, among others.
Etymology / Origin
The name “conichalcite” derives from the Greek word kónos meaning “cone” and the Greek word chalkos meaning “copper,” referring to its typical greenish‑copper coloration and the habit of forming acicular or fibrous aggregates that may appear cone‑shaped.
Characteristics
| Property | Description |
|---|---|
| Crystal system | Orthorhombic |
| Space group | Pbnm |
| Typical color | Pistachio‑green, dark green, blue‑green; sometimes brownish‑green due to intergrowths |
| Habit | Prismatic, acicular, fibrous, granular; often forms radial aggregates |
| Cleavage | Poor |
| Fracture | Subconchoidal |
| Hardness (Mohs) | 3–4 |
| Luster | Vitreous to greasy |
| Diaphaneity | Transparent to translucent |
| Specific gravity | Approximately 4.1 g·cm⁻³ |
| Optical properties | Biaxial positive; refractive indices nα ≈ 1.738, nβ ≈ 1.748, nγ ≈ 1.757; birefringence δ ≈ 0.019 |
| Fluorescence | Weak to moderate green fluorescence under short‑wave UV light |
Conichalcite is soluble in acids, releasing arsenic into solution, which has implications for environmental monitoring of arsenic contamination in mining areas.
Related Topics
- Arsenate minerals – A broader class of minerals containing the AsO₄³⁻ anion, including olivenite, scorodite, and adamite.
- Supergene enrichment – The geochemical process by which primary sulfide minerals are altered near the Earth’s surface, often producing secondary minerals such as conichalcite.
- Copper mineralogy – Study of copper‑bearing minerals, of which conichalcite is a minor but diagnostically useful member.
- Environmental arsenic – Issues concerning the mobility of arsenic from minerals like conichalcite in contaminated soils and water.
References: data compiled from standard mineralogical literature and the International Mineralogical Association (IMA) database.