Glass-(Er)

Chemical formula: Ca₂ErAl(PO₄)₄(OH)·7H₂O

Glass-(Er) is an extremely rare, radioactive erbium phosphate, occurring as microscopic, pinkish crystals in pegmatites.

## Characteristics Glass-(Er) is an extremely rare mineral from the phosphate group, chemically classified as a hydrated erbium, calcium, and aluminum phosphate. It occurs as very small, tabular or bladed crystals, rarely exceeding 0.3 mm in length. It typically forms small aggregates or rosettes. Its identification requires advanced analytical methods due to its microscopic size and rarity. ## Physical Properties The crystals are brittle and exhibit a vitreous luster. The mineral is radioactive. Due to the small size of the crystals, many physical properties, such as hardness or density, have not been precisely measured. ## Colors and Varieties Glass-(Er) is characterized by a pale, pinkish color. It has no known varieties. ## History and Name The mineral was named in honor of Jewell J. Glass (1894–1960), an American mineralogist and chemist who worked for the United States Geological Survey (USGS). The suffix -(Er) in the name indicates the dominance of erbium among the rare earth elements in its chemical composition. It was approved as a new mineral species by the IMA in 2022. ## Applications Due to its extreme rarity and microscopic size, Glass-(Er) has no practical or commercial applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Luster
Vitreous
Streak
White
Cleavage
Good on {010}
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Practical identification of Glass-(Er) is impossible without advanced laboratory equipment. Preliminary identification in the field or under a microscope relies on finding a pale, pinkish mineral with a tabular habit in a specific geological environment (granitic pegmatites) at a known locality. Final confirmation requires chemical analysis (EDS) and crystallographic analysis (XRD). ## Distinguishing from Similar Minerals It can be confused with other microscopic secondary minerals found in pegmatites, such as other rare earth phosphates. Differentiation is based on chemical composition analysis, which shows the dominance of erbium, a unique characteristic of this mineral. ## Crystal Forms It forms very small, thin, tabular crystals, often with a hexagonal or rectangular outline. These crystals group into small, rosette-like or radial aggregates.

Geological environment

## Genesis Glass-(Er) is a secondary mineral, formed in the weathering zones of granitic pegmatites rich in rare earth elements. It forms as a result of hydrothermal alteration or weathering of primary minerals containing phosphorus and rare earth elements, such as xenotime or euxenite. ## Mineral Associations It co-occurs with minerals typical of pegmatites, such as quartz, microcline, albite, muscovite, as well as rarer minerals containing rare earth elements, e.g., xenotime-(Y). ## Localities The only confirmed occurrence worldwide (type locality) is the Little Patsy quarry, located in the Jefferson Mountains in Jefferson County, Colorado, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen primarily depends on the size and development of the crystals and the richness of their occurrence on the rock matrix. Specimens with clearly visible, sharp crystals forming aesthetic aggregates are most valued. A contrasting matrix (e.g., dark smoky quartz) enhances visual appeal. The purity and intensity of the pink color are also important, although difficult to assess due to the size. ## Popular Localities The only source of specimens is the type locality – the Little Patsy quarry in Colorado, USA. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Specimens should not be cleaned mechanically or chemically. Any contaminants, such as dust, can only be removed using compressed air from a safe distance. ## What to Avoid Avoid contact with water, chemicals, ultrasound, and all forms of mechanical cleaning (e.g., brushes), which could irrevocably damage the delicate crystals. The mineral is brittle and sensitive to shocks. ## Storage Specimens should only be stored in specialized "micromount" boxes, protecting them from dust, shocks, and mechanical damage. As a radioactive mineral, it should be stored with appropriate precautions, away from other radiation-sensitive minerals.

Sources

Read more