Glass-(Yb)

Chemical formula: YbCu(AsO₄)(OH)

A very rare ytterbium-copper arsenate, named after the collector Charles Glass, discovered in the Tsumeb mine in Namibia.

## Characteristics Glass-(Yb) is an arsenate belonging to the adelite-descloizite group. It forms elongated, prismatic crystals up to 0.2 mm long, most often occurring as radial or divergent aggregates. Its color is typically pale yellowish-green. It is a secondary mineral, found in voids within tennantite-quartz ore. ## Physical Properties This mineral is characterized by a hardness estimated at approximately 5 on the Mohs scale and a calculated density of 6.01 g/cm³. The luster is vitreous to greasy. It is brittle, and its crystals are translucent. ## Colors and Varieties The only known color of this mineral is pale yellowish-green. No varieties have been distinguished. ## History and Name The mineral's name honors Charles Glass (1827–1863), an American mineral collector and dealer. The suffix -(Yb) indicates the dominance of ytterbium in its chemical composition. It was officially approved by the International Mineralogical Association (IMA) in 2022 under number IMA2022-055. ## Applications Due to its extreme rarity and microscopic size, Glass-(Yb) has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromount mineral collectors.

Properties

Mohs hardness
~5
Luster
Vitreous to greasy
Streak
Light greenish yellow
Density
6.01
Cleavage
None
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Visual identification is impossible. Reliable identification requires advanced analytical methods, such as energy-dispersive spectroscopy (EDS/WDS) to confirm its unique chemical composition (dominance of Yb, presence of Cu and As) and X-ray diffraction (XRD) for crystal structure analysis. ## Distinguishing from Similar Minerals It can be confused with other rare, secondary arsenates from Tsumeb, especially other greenish members of the adelite-descloizite group. Final differentiation from minerals such as zincolivenite, duftite, or conichalcite requires chemical analysis to show the dominance of ytterbium. ## Crystal Forms It forms tiny, prismatic crystals that combine into characteristic, radial aggregates.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zone of a polymetallic hydrothermal deposit. It crystallizes in small voids and fissures in ore composed mainly of tennantite and quartz. ## Mineral Associations It co-occurs directly with tennantite and quartz, which form the matrix for its crystals. ## Localities The only confirmed locality in the world is its type locality – the famous Tsumeb mine in the Oshikoto region of Namibia.

Rarity

Extremely rare

For collectors

## Quality Criteria For "micromount" minerals such as Glass-(Yb), specimens with sharp, well-formed crystals creating aesthetic aggregates are most highly valued. The size and richness of these aggregates on the matrix, as well as minimal damage, are also important. Due to its rarity, any specimen with visible crystals is considered valuable. ## Popular Localities The only source of specimens is the Tsumeb mine in Namibia, which is currently closed. The material comes exclusively from historical collections.

Care and storage

## Cleaning Micromount specimens should be cleaned with the utmost care, preferably using compressed air from a safe distance to remove dust. Avoid contact with water and any chemicals. Do not use ultrasonic cleaners. ## What to Avoid As an arsenate, the mineral is toxic – avoid inhaling dust and contact with the mouth. The crystals are very small and brittle, susceptible to mechanical damage. Protect from high temperatures and sudden changes in temperature. ## Storage The safest way to store it is in a tightly sealed "micromount" box, protecting it from dust, moisture, and mechanical damage. Each specimen should be properly labeled.

Sources

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