Olivenite
Chemical formula: Cu₂(AsO₄)(OH)
Olivenite is a rare arsenic and copper mineral, characterized by its olive-green color and often occurring as small crystals or aggregates.
Description
## Characteristics Olivenite is a copper arsenate that typically forms small, acicular or prismatic crystals, often aggregated into radial or spherical clusters. Its name refers to its characteristic olive-green color, although this mineral can also occur in shades of yellow, brown, grayish-green, and even grayish-white. Olivenite crystals are usually small, but their intense color makes them easily recognizable. ## Physical Properties This mineral has a hardness of 3 on the Mohs scale, meaning it is relatively soft. It has a vitreous to adamantine luster, and its density is approximately 4.46 g/cm³. Olivenite is transparent to opaque, and its streak is olive-green to brown. ## Colors and Varieties The most typical color of olivenite is olive-green, from which its name is derived. It can also occur in shades of yellow, brown, grayish-green, and grayish-white. In transmitted light, this mineral is light green. No specific commercial varieties are distinguished. ## History and Name Olivenite was described in 1786. Its name comes from its characteristic olive-green color, which is most typical for this mineral. ## Uses Olivenite has no industrial applications due to its rarity and small crystal sizes. It is a prized collector's mineral, particularly sought after for its intense color and aesthetic crystalline forms.
Diagnostic features
## Identification Olivenite can be identified by its characteristic olive-green color, vitreous to adamantine luster, and relatively low hardness (3 on the Mohs scale). It often occurs as small, acicular or prismatic crystals forming radial or spherical aggregates. The mineral's streak is olive-green to brown. ## Distinguishing from Similar Minerals Olivenite can be confused with some copper minerals, such as malachite or azurite, but its olive color and lack of reaction with hydrochloric acid (as in the case of malachite) allow for differentiation. Libethenite can also be similar, but olivenite usually has a more intense color and a different crystalline form. ## Crystal Forms Olivenite most often occurs as small, acicular or prismatic crystals. These crystals often form radial, spherical, or reniform aggregates. Well-formed, single crystals are less common.
Geological environment
## Genesis Olivenite is a secondary mineral, formed in the oxidation zones of copper deposits containing arsenic. It forms as a result of the weathering processes of other copper and arsenic minerals in an oxygen-rich environment. ## Mineral Associations Olivenite often co-occurs with other secondary minerals of the oxidation zone, such as azurite, malachite, chrysocolla, limonite, quartz, and also with arsenic minerals, e.g., pharmacosiderite. ## Localities Known localities of olivenite include the mines in Tsumeb, Namibia, where some of the best specimens have been found. It also occurs in Cornwall, England, in the Tintic district of Utah, USA, as well as in Chile and Australia.
Rarity
Common
Collector aspects
## Quality Criteria The most prized olivenite specimens are characterized by an intense, vivid olive-green color. The aesthetics of the crystalline form are also important – well-formed, distinct crystals or attractive radial or spherical aggregates are more desirable. The size of the specimen, although usually small, also affects its value. Purity and absence of mechanical damage are crucial. ## Popular Localities The most sought-after olivenite specimens come from the mines in Tsumeb, Namibia, where they occur as well-formed crystals with intense color. Specimens from Cornwall, England, are also valued by collectors.
Care and storage
## Cleaning Olivenite is a relatively soft mineral, so it should be cleaned gently. It is best to use a soft brush and lukewarm water. Distilled water can also be used to avoid hard water deposits. ## What to Avoid Avoid using strong chemical agents that can damage the mineral's surface. Olivenite is sensitive to acids. Prolonged exposure to direct sunlight can cause color fading, so it is recommended to store it in a shaded place. High temperatures and sudden temperature changes can also be harmful. ## Storage Olivenite specimens are best stored in enclosed display cases or boxes to protect them from dust and mechanical damage. Due to its softness, avoid contact with harder minerals that could scratch it. Ideal storage is in a dry place with stable temperature.