O'danielite

Chemical formula: Na☐Zn2+Zn2+2(As5+O4)[As5+O3(OH)]2

O'danielite is an extremely rare sodium zinc arsenate, forming purple, tabular crystals, known exclusively from the Tsumeb mine in Namibia.

Description

## Characteristics O'danielite is a rare mineral from the arsenate group, chemically classified as a sodium zinc arsenate. It forms small, thin, tabular or bladed crystals, rarely exceeding 1 mm in length. These crystals often occur as radial or subparallel aggregates, forming small clusters on the host rock surface. A characteristic feature of the mineral is its intense, purple or violet color. ## Physical Properties The mineral exhibits a vitreous luster. It is transparent to translucent. Its density, calculated based on chemical composition and unit cell parameters, is approximately 4.45 g/cm³. Hardness has not been determined due to the small size and rarity of the crystals. ## Colors and Varieties O'danielite occurs in a uniform range of colors from violet to purple. No color varieties or commercial varieties are known. ## History and Name The mineral was first described in 1981 by Paul Keller, Heinz Hess, and Pete J. Dunn. Its name commemorates Herbert O'Daniel (1903-1977), a German mineralogist and crystallographer from the University of Frankfurt am Main, in recognition of his contributions to mineralogy. ## Uses Due to its extreme rarity, o'danielite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced systematic and specialized collections.

Diagnostic features

## Identification The most important features for identifying o'danielite are its intense purple color, thin, tabular crystals forming small aggregates, and its unique locality. Vitreous luster and a pale purple streak are also helpful. However, definitive confirmation requires advanced analytical methods, such as chemical composition analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals O'danielite can be confused with other purple arsenates from Tsumeb, such as prosperite. However, prosperite forms crystals with a different habit (usually prismatic) and crystallizes in the monoclinic or triclinic system, depending on the polymorph. Visual distinction of these minerals can be difficult and often requires laboratory analysis. ## Crystal Forms O'danielite crystals are thin, tabular, elongated, and flattened. They usually occur as small, radially diverging or subparallel groups and aggregates on the surface of the host rock.

Geological environment

## Genesis O'danielite is a secondary mineral that formed in the oxidation zone of the polymetallic deposit in Tsumeb. It crystallized in vugs and fissures of heavily corroded sulfide ore, deposited in dolomitic rocks. ## Mineral Associations This mineral occurs in association with other rare secondary arsenates, primarily prosperite, gaitite, köttigite, and tsumcoite. ## Localities The only confirmed locality for o'danielite in the world is its type locality – the Tsumeb mine in the Oshikoto region of Namibia. This mine is currently closed, making the acquisition of new specimens impossible.

Rarity

Extremely rare

Collector aspects

## Quality Criteria The collector's appeal of o'danielite specimens depends on several factors. Specimens with well-formed, sharp crystals of intense, purple color are most highly valued. The size of the aggregates and the abundance of the mineral on the rock matrix are also important. Specimens with well-defined crystals, contrasting with a light host rock, and co-occurring with other rare minerals from Tsumeb, achieve the highest value. ## Popular Localities Since the Tsumeb mine in Namibia is the only known source of o'danielite, all specimens originate from this single, historic locality. Specimens from Tsumeb are classics and among the most sought-after minerals by collectors worldwide.

Care and storage

## Cleaning O'danielite specimens should only be dry-cleaned, using a soft brush to remove dust. Due to its probable chemical sensitivity, contact with water and any cleaning agents should be avoided. The crystals are very small and fragile, requiring maximum caution. ## What to Avoid As an arsenate, the mineral is toxic. Inhaling dust should be avoided, and hands should be washed after each contact with the specimen. It must not be heated or exposed to acids and other chemicals. It should be protected from prolonged exposure to direct sunlight, which may cause color fading. ## Storage It is recommended to store specimens in closed, labeled containers (e.g., micromount type) to protect them from dust, mechanical damage, and accidental contact. A stable environment with controlled, low humidity is best.