Derriksite

Chemical formula: Cu<sup>2+</sup><sub>4</sub>(U<sup>6+</sup>O<sub>2</sub>)(Se<sup>4+</sup>O<sub>3</sub>)<sub>2</sub>(OH)<sub>6</sub>

Derriksite is a rare uranyl copper selenite, forming tiny, tabular crystals of an intense green color.

## Characteristics Derriksite is a secondary mineral from the selenite group, occurring in the oxidation zones of uranium-selenium deposits. It forms very small, tabular or bladed crystals, rarely exceeding 1 mm in length. It usually appears as dispersed aggregates, coatings, or thin crusts on the host rock. Its intense green color is characteristic and results from the presence of copper and uranyl ions in its structure. ## Physical Properties Derriksite crystals exhibit a vitreous luster. The mineral is translucent. Due to the small size of the crystals, many of its physical properties, such as hardness or density, have not been precisely determined. ## Colors and Varieties Derriksite occurs in a uniform, emerald-green or simply green color. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1971 by Michel Deliens and Paul Piret. Its name commemorates Jean-Marie François "Rik" Joseph Derriks (1912-1990), a Belgian geologist and general manager at Union Minière du Haut Katanga, for his contributions to the study of uranium deposit geology in the Democratic Republic of Congo. ## Uses Derriksite, due to its extreme rarity and microscopic crystal size, has no industrial application. It is solely an object of scientific interest and is valued by specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Light green
Density
4.74
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Derriksite can be identified by its characteristic, intense green color, tabular crystal habit, and occurrence in association with other secondary uranium and selenium minerals. Due to its microscopic size, definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) or EDS spectroscopy. ## Distinguishing from Similar Minerals It can be confused with other green, secondary uranyl minerals such as cuprosklodowskite, torbernite, or brochantite. It differs from cuprosklodowskite and torbernite in crystal habit (derriksite forms tabular crystals, not needles or square plates). It is distinguished from brochantite by the presence of selenium and uranium, as well as significantly higher radioactivity. Chemical composition analysis is key. ## Crystal Forms Derriksite crystals are very small, usually up to 1 mm in length. They take the form of thin, rectangular tablets or blades, often with oblique terminations. They occur as single, dispersed crystals or form small, radial aggregates.

Geological environment

## Genesis Derriksite is a secondary mineral, formed in the oxidation (weathering) zone of hydrothermal uranium-selenium deposits rich in copper. It crystallizes as a result of reactions of solutions containing selenium, uranium, and copper, originating from the weathering of primary ores, under low temperature and pressure conditions. ## Mineral Associations This mineral co-occurs with other secondary selenites and sulfates. It is most often accompanied by demesmaekerite, marthozite, guilleminite, cuprosklodowskite, as well as chalcomenite, malachite, and brochantite. ## Localities The most important and also the type locality for derriksite is the Musonoi mine near Kolwezi, in Lualaba province (formerly Katanga) in the Democratic Republic of Congo. This is the only confirmed and well-documented locality for this mineral in the world.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of derriksite primarily depends on the quality and size of the crystals, which is a rarity for this mineral. The most prized specimens are those with well-formed, sharp, undamaged crystals of an intense green color, standing out clearly from the host rock. A rich association with other rare selenites, such as demesmaekerite or marthozite, is also important. ## Popular Localities The only source of collector specimens of derriksite is its type locality – the Musonoi mine in the Democratic Republic of Congo. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Derriksite specimens are extremely delicate and usually microscopic in size. They should not be cleaned mechanically or chemically. Any attempts at cleaning risk irreversible damage to the mineral. If dust removal is necessary, it can be done very carefully with a soft brush or a photographic air blower, avoiding direct contact with the crystals. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and sudden temperature changes. The mineral is radioactive and should be handled with appropriate precautions, avoiding inhalation of dust and direct skin contact. ## Storage Specimens should be stored in stable conditions, away from sunlight, moisture, and heat sources. The safest form of storage is specialized "micromount" boxes, which protect delicate crystals from mechanical damage and dust. Due to radioactivity, specimens should be stored in appropriately labeled containers, away from areas of constant human presence.

External references

Sources

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