Tertschite

Chemical formula: Ca<sub>4</sub>B<sub>10</sub>O<sub>19</sub>·20H<sub>2</sub>O

Tertschite is a very rare, hydrated calcium borate, forming colorless or white, acicular crystals and aggregates.

## Characteristics Tertschite is a mineral from the borate group, chemically a hydrated calcium borate. It occurs extremely rarely, forming small, acicular or bladed crystals, which often arrange into radial or tangled aggregates. Individual crystals are usually colorless or white and can reach up to 2 mm in length. ## Physical Properties Tertschite crystals are characterized by a vitreous luster. They are transparent to translucent. This mineral is relatively soft, with a Mohs hardness of approximately 2. It is also quite light, with a density close to 1.89 g/cm³. ## History and Name The mineral was first described in 1953 by Heinz Meixner. The name was given in honor of Franz Tertsch (1884–1960), an Austrian mineralogist and crystallographer, professor of mineralogy at the University of Vienna. ## Uses Due to its extreme rarity and small crystal size, tertschite has no commercial or industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
White
Density
1.89
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Tertschite is difficult to identify visually without specialized equipment. It is recognized by its habit – in the form of small, acicular or bladed crystals forming radial aggregates. Its occurrence in a specific geological environment, in association with other borates, is also characteristic. ## Differentiation from Similar Minerals It can be confused with other rare, white, acicular borates, such as gowerite or ulexite. Ulexite often exhibits a characteristic fiber-optic effect (the so-called "television stone"), which is absent in tertschite. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Crystal Forms Crystals are elongated in the form of needles or blades, often flattened. They usually occur as radial or haphazardly tangled clusters and aggregates.

Geological environment

## Genesis Tertschite is a mineral of sedimentary origin. It forms in evaporite basins (salt lakes) in dry and hot climates, as a result of precipitation from solutions rich in boron and calcium. It is a product of the late stage of evaporation. ## Mineral Associations It co-occurs with other borate minerals, such as colemanite, hydroboracite, gowerite, ulexite, as well as gypsum and calcite. ## Localities The only confirmed and most important locality of tertschite in the world is the borate deposits in the Bigadiç region, in Balıkesir Province, Turkey. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the size and quality of the formed aggregates are most important. Specimens with distinct, radial clusters of acicular crystals, contrasting with the rock matrix, are most valued. Due to the microscopic size of the crystals, specimens are usually small (so-called microminerals). ## Popular Localities The only source of tertschite specimens is the Bigadiç region in Turkey. All specimens available on the collector's market come from the borate mines there.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using a soft brush to remove dust. Due to its water solubility, contact with water and other liquids should be avoided. Wet cleaning is absolutely not recommended. ## What to Avoid Avoid contact with water and any chemicals that could damage or dissolve the mineral. It is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. Due to its low hardness, it is very susceptible to mechanical damage. ## Storage Tertschite specimens should be stored under stable conditions, preferably in closed, airtight containers (e.g., "perky box" type), to protect them from dust, moisture, and physical damage. Avoid storing in places with fluctuating air humidity.

Sources

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