Luinaite-(OH)

Chemical formula: (Na,◻)(Fe²⁺,Mg)₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

Luinaite-(OH) is a very rare, dark green to black mineral from the tourmaline group, discovered in the Mount Cleveland mine in Tasmania.

## Characteristics Luinaite-(OH) is a mineral belonging to the tourmaline supergroup, specifically to the alkali group. It forms very small, prismatic crystals, usually not exceeding 0.5 mm in length, which often occur in radial or fibrous aggregates. Its color ranges from dark green to black, which is typical for iron-rich tourmalines. ## Physical Properties This mineral is characterized by a vitreous luster. It is opaque. Due to the small size of the crystals, precise determination of hardness and density is difficult; however, as a member of the tourmaline group, its hardness can be estimated at approximately 7 on the Mohs scale. ## Colors and Varieties The observed colors of luinaite-(OH) are dark green and black. No named varieties of this mineral have been distinguished. ## History and Name The mineral's name refers to its discovery locality – the Mount Cleveland mine near the town of Luina in Tasmania (Australia). The "-(OH)" suffix in the name indicates the dominance of the hydroxyl group at a specific site in its crystal structure, in accordance with tourmaline group nomenclature rules. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2017. ## Uses Luinaite-(OH) has no industrial applications. Its significance is purely scientific and collectible, as a very rare member of the extensive tourmaline group.

Properties

Luster
Vitreous
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of luinaite-(OH) is extremely difficult and impossible without advanced analytical methods, such as spectroscopy and chemical analysis (EDS/WDS). Preliminary identification based on appearance (dark, prismatic tourmaline crystals) and mineral associations at the type locality is possible, but requires laboratory confirmation. ## Distinguishing from Similar Minerals Visually, it is indistinguishable from other black or dark green tourmalines, such as schorl, dravite, or foitite. The only way to definitively distinguish it is through precise chemical analysis, which will reveal the specific combination of sodium, iron, and aluminum characteristic of luinaite-(OH), and the dominance of the (OH) group at the appropriate structural site. ## Crystal Forms It forms small, columnar or prismatic crystals, often terminated by trigonal pyramids. They usually occur as radial or tangled fibrous aggregates.

Geological environment

## Genesis Luinaite-(OH) forms as a result of hydrothermal processes. At its type locality (Mount Cleveland mine), it was found in quartz-tourmaline veins cutting sulfide deposits (mainly pyrite and pyrrhotite) within carbonate rocks. ## Mineral Associations This mineral coexists with quartz, pyrite, pyrrhotite, fluorite, cassiterite, chalcopyrite, and other tourmalines. ## Localities The only confirmed occurrence of luinaite-(OH) in the world is its type locality: Mount Cleveland mine, Luina, Heazlewood district, Tasmania, Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" mineral, the quality of a specimen is primarily determined by the abundance and development of crystals within the microscope's field of view, as well as their association with other minerals. The most desirable specimens are those with clearly formed, radial aggregates on a contrasting background, e.g., on quartz. The certainty of identification, supported by analysis, is also crucial. ## Popular Localities The only source of specimens is the Mount Cleveland mine in Tasmania. Material from this locality is extremely rare on the collector's market.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to extreme rarity and small crystal size, any mechanical (brushes) or chemical cleaning should be avoided. ## What to Avoid Avoid contact with chemicals, acids, and detergents. Do not subject specimens to ultrasonic cleaning. Protect from high temperatures and sudden temperature changes. ## Storage Luinaite-(OH) specimens are typically microscopic and fragile. It is best to store them in their original, sealed "micromount" box, protecting them from dust, shocks, and direct sunlight. Stable temperature and low humidity are recommended.

External references

Sources

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