Greenwoodite

Chemical formula: Ba₂-x(V³⁺OH)xV³⁺₉(Fe³⁺,Fe²⁺)₂Si₂O₂₂

Greenwoodite is a very rare silicate group mineral, found as tiny, black, hexagonal crystals in manganese deposits.

## Characteristics Greenwoodite is an extremely rare mineral, occurring as very small, tabular crystals with a hexagonal outline. Its crystals rarely exceed 0.2 mm in diameter. It is black and opaque, with a metallic or submetallic luster. It usually forms single, scattered crystals or small aggregates on the surface of other minerals. ## Physical Properties This mineral is characterized by a metallic luster and black color. Its hardness and density have not been precisely measured due to the small size of the crystals. It is brittle. ## History and Name Greenwoodite was named after Hugh Greenwood (born 1931), a professor of petrology at the University of British Columbia in Canada, for his contributions to mineralogy and petrology. It was approved as a new mineral by the IMA in 1992. ## Uses Due to its extreme rarity and microscopic size, greenwoodite has no commercial or industrial applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals (so-called micromounts).

Properties

Mohs hardness: 5
Color: Black
Luster: Metallic
Streak: Black
Density: 4.81
Cleavage: {001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of greenwoodite is practically impossible. It requires specialized analytical methods, such as chemical analysis using an electron microprobe (EDS/WDS) and X-ray diffraction (XRD). Visually, it can be suspected based on its characteristic locality (Hoskins mine, NSW, Australia), black color, metallic luster, and tiny, hexagonal crystals. ## Distinguishing from similar minerals It can be confused with other tiny, black minerals with a metallic luster, such as hematite, magnetite, or some spinels. Certain differentiation is only possible using advanced analytical techniques. ## Crystal forms It forms very small, thin, tabular crystals with a hexagonal outline. Crystals occur as single, isolated flakes on the surface of the host rock.

Geological environment

## Genesis Greenwoodite forms as a result of metamorphic processes within manganese and iron ore deposits. It occurs in rocks rich in quartz, hematite, and barium minerals. ## Mineral associations This mineral co-occurs with minerals such as quartz, hematite, celsian, hyalophane, richterite, namansilite, and norrishite. It is most often found on quartz or hematite crystals. ## Localities The only confirmed occurrence of greenwoodite in the world is its type locality - the Hoskins mine in Gowen County, New South Wales, Australia.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of greenwoodite specimens is primarily assessed based on the presence of well-formed, sharp, and undamaged crystals, even if they are microscopic in size. The most desirable specimens are those where the black greenwoodite crystals contrast with a lighter background, such as white quartz. Crystal size, although always small, is also important - larger (above 0.1 mm) and well-formed crystals are more highly valued. ## Popular localities The only source of specimens is the Hoskins mine in New South Wales, Australia. All specimens available on the collector's market come from this single locality.

Care and storage

## Cleaning Specimens containing greenwoodite, which are typically micromounts, should not be cleaned mechanically or chemically. The safest method for dust removal is to use compressed air designed for cleaning optics or electronics, applied from a safe distance. ## What to avoid Avoid contact with any chemicals, including water and acids. The crystals are extremely small and brittle, so avoid vibrations, shocks, and touching the specimen's surface. ## Storage Specimens should be stored exclusively in specialized micromount boxes that protect them from dust, moisture, and mechanical damage. Store in stable room conditions, away from heat and moisture sources.