Magnesiokoritnigite

Chemical formula: Mg(As₅+O₃OH)·H₂O

Magnesiocoritnigite is a rare hydrated magnesium arsenate, forming colorless to white, acicular crystals, found in association with other arsenates.

## Characteristics Magnesiocoritnigite is a hydrated magnesium arsenate, belonging to the coritnigite group. It occurs as very small, acicular or bladed crystals, usually not exceeding 1 mm in length. These crystals form radial aggregates, rosettes, or are randomly scattered on the surface of the host rock. It is a colorless to white mineral with a vitreous luster. ## Physical Properties This mineral is characterized by a hardness of approximately 3 on the Mohs scale. It is brittle, and its crystals are flexible. The calculated density is about 3.06 g/cm³. It possesses perfect cleavage in one direction. ## Colors and Varieties It is usually colorless, but can take on shades of white. No varieties of this mineral have been distinguished. ## History and Name The name magnesiocoritnigite refers to its chemical composition – the dominance of magnesium (magnesio) and its structural similarity to coritnigite. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1978. It was described by German mineralogists Paul Keller, Heinz Hess, and Pete J. Dunn based on samples from the Tsumeb mine in Namibia. ## Applications Due to its extreme rarity and microscopic crystal sizes, magnesiocoritnigite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities (so-called "systematists" and "locality" collectors).

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: White
Density: 3.06
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Triclinic

Diagnostic features

## Identification Identification of magnesiocoritnigite under amateur conditions is practically impossible and requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). Preliminary identification is based on crystal habit (small, acicular, radial aggregates), colorless or white color, and co-occurrence with other rare arsenates in known localities. ## Distinguishing from Similar Minerals It can be confused with other white, acicular secondary minerals, such as gypsum, hemimorphite, or other rare arsenates (e.g., pharmacolite, coritnigite). Definitive differentiation is only possible through chemical analysis, which will show the presence of magnesium and arsenic in the absence of zinc (unlike coritnigite) or calcium (unlike pharmacolite). ## Crystal Forms Crystals are elongated along the b-axis, forming acicular or bladed habits. They typically occur as radial or disordered clusters and aggregates on the rock surface.

Geological environment

## Genesis Magnesiocoritnigite is a secondary arsenate mineral that forms in the oxidation (weathering) zones of polymetallic ore deposits rich in arsenic. It forms as a result of the reaction of arsenic-bearing solutions with magnesium-rich minerals, such as dolomite, under conditions of low temperature and pressure. ## Mineral Associations This mineral co-occurs with other arsenates. In the type locality (Tsumeb), it was found in association with coritnigite, ludlockite, prosperite, tsumcorite, zincolivenite, warikahnite, germanite, and tennantite. In Sterling Hill (USA), it occurs with franklinite, willemite, and other arsenates. ## Localities The most important and confirmed occurrences of this very rare mineral are: - Tsumeb Mine in Namibia - the type locality, from which the best-formed specimens originate. - Sterling Hill Mine in Ogdensburg, New Jersey, USA - the second confirmed locality in the world.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a magnesiocoritnigite specimen is primarily assessed based on the richness and aesthetics of the crystal aggregates. Most prized are specimens with distinct, radial clusters of acicular crystals, well-separated from each other and set on a contrasting rock matrix. Crystal size, although always microscopic, is also important – longer needles are more desirable. The absence of damage to the delicate crystals is also crucial. ## Popular Localities Specimens from the type locality – the Tsumeb mine in Namibia – are by far the most valued and sought after by collectors. Specimens from Sterling Hill are equally rare, but those from Tsumeb are considered classic for this mineral.

Care and storage

## Cleaning Specimens should only be cleaned very carefully, using compressed air to remove dust. Contact with water is not recommended due to the mineral's delicacy and potential solubility. Ultrasonic cleaners and any mechanical cleaning should be avoided. ## What to Avoid Avoid contact with all chemicals, especially acids, which can damage it. The mineral is brittle and sensitive to shocks and temperature changes. It should not be exposed to direct sunlight. ## Storage Magnesiocoritnigite specimens, as microminerals, should be stored in specialized "micromount" boxes that protect them from mechanical damage, dust, and moisture. Avoid storage in areas with fluctuating humidity.

Sources

IMA Mineral List (CNMNC)