Cornubite
Chemical formula: Cu<sup>2+</sup><sub>5</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>4</sub>
Cornubite is a rare copper arsenate, forming characteristic apple-green aggregates and crusts.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- Light green
- Density
- 4.64-4.66
- Cleavage
- None
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Triclinic
Diagnostic features
## Identification Cornubite is primarily identified by its characteristic apple-green color and mode of occurrence - most often as crusts, earthy aggregates, or radial aggregates. Its origin from the oxidation zones of copper and arsenic ore deposits is also key. ## Distinguishing from Similar Minerals Cornubite is difficult to distinguish from other green, secondary copper minerals, such as Cornwallite, Pseudomalachite, or Tyrolite. Cornwallite is its monoclinic polymorph and often has a darker, emerald-green hue. Reliable differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Cornubite is an amorphous mineral or occurs as very fine, poorly formed crystals that create radial, spherulitic, botryoidal aggregates, as well as massive and earthy crusts.
Geological environment
## Genesis Cornubite is a secondary mineral, forming in the oxidation (weathering) zones of copper ore deposits that also contain arsenic-rich minerals. It forms as a result of surface water action on primary sulfides and arsenides. ## Mineral Associations It most often co-occurs with other secondary copper and arsenic minerals. Its typical associated minerals include: Cornwallite, Olivenite, Chenevixite, Tyrolite, Malachite, Azurite, as well as Quartz and iron oxides (e.g., Goethite). ## Localities The most important cornubite localities in the world are the historical mines in Cornwall (Great Britain), from which it takes its name. It is also found in other locations, such as the Clara mine in the Black Forest (Germany), in the Příbram area (Czech Republic), and in small quantities in some mines in Arizona and Utah (USA).
Rarity
Rare
For collectors
## Quality Criteria The most valued specimens by collectors are those where cornubite forms well-defined, radial aggregates or spherulites of intense, apple-green color. The contrast with the rock matrix and the presence of rare associated minerals are also important. Due to its microcrystalline nature, the size of individual "crystals" is not a key criterion; rather, the aesthetics and richness of the entire aggregate are important. ## Popular Localities Classic and most sought-after specimens come from the historical mines of Cornwall in Great Britain. Specimens from the Clara mine in Germany are also highly valued in the collector's market.
Care and storage
## Cleaning Cornubite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its possible reactivity, wet cleaning is not recommended, and if absolutely necessary, a small amount of distilled water should be used, and the specimen immediately and thoroughly dried. Always wash hands after contact with the mineral due to its arsenic content. ## What to Avoid Avoid contact with all chemicals, especially acids, which can damage it. The mineral is sensitive to high temperatures and humidity. It should not be exposed to prolonged direct sunlight. ## Storage Cornubite specimens are best stored in closed, dry containers or display cases, away from sources of moisture and sudden temperature changes. It is advisable to isolate it from other minerals that could scratch it.