Pertsevite-(OH)

Chemical formula: Mg<sub>₂</sub>BO<sub>₃</sub>(OH)

Pertsevite-(OH) is a very rare magnesium borate, forming colorless, tabular crystals in magnesian skarns.

## Characteristics Pertsevite-(OH) is an extremely rare mineral from the borate group, chemically classified as a magnesium hydroxyborate. It occurs as very small, colorless, tabular or bladed crystals, usually not exceeding 0.3 mm in length. The crystals are transparent and characterized by a vitreous luster. Due to its size and rarity, it is a mineral known primarily in scientific and specialized circles. ## Physical Properties This mineral has a hardness of approximately 5 on the Mohs scale. Its crystals are transparent and have a vitreous luster. The density calculated based on the formula and unit cell parameters is approximately 2.83 g/cm³. ## Colors and Varieties Pertsevite-(OH) is colorless. No colored varieties or trade names are known. ## History and Name The mineral's name refers to its structural and chemical similarity to pertsevite-(F), with which it forms a series. The -(OH) suffix indicates the dominance of the hydroxyl group in its chemical composition. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2002 under number IMA2002-033. Its scientific description was published in 2004 by a research team, including Igor V. Pekov.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.83
Cleavage: Good on {100} and {010}
Fracture: Uneven
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of pertsevite-(OH) is impossible without advanced analytical methods. Due to its occurrence as microscopic, colorless crystals, it requires chemical analysis (e.g., using an electron microprobe) and structural analysis (X-ray diffraction) to confirm its composition and crystal structure. It is distinguished by the presence of boron, magnesium, and the hydroxyl group. ## Distinguishing from Similar Minerals It can be confused with other colorless borates or silicates found in similar environments, such as kotoite, clinokotoite, sinhalite, or pertsevite-(F). Differentiation from pertsevite-(F) requires precise chemical analysis to determine whether the hydroxyl group (OH) or fluorine (F) predominates. Other co-occurring minerals, such as spinel or forsterite, usually have different crystal forms and higher hardness. ## Crystal Forms Pertsevite-(OH) forms small, tabular or bladed crystals, often flattened. It occurs as single, dispersed crystals or small aggregates within the host rock.

Geological environment

## Genesis Pertsevite-(OH) is a mineral of metamorphic origin. It forms in high-temperature magnesian skarns, which developed at the contact of granitoid intrusions with dolomites. It is a product of boron metasomatism in a silica-poor environment. ## Mineral Associations This mineral co-occurs with other borates and minerals typical of magnesian skarns. It is most often accompanied by: kotoite, pertsevite-(F), spinel, forsterite, calcite, dolomite, fluorite, and minerals from the humite group. ## Localities The only confirmed and described occurrence of pertsevite-(OH) (type locality) is the Snezhnoye iron and boron deposit in the Tas-Khayakhtakh massif in Yakutia (Sakha Republic), Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, pertsevite-(OH) is not evaluated according to typical criteria such as size or color. For collectors specializing in rare species (so-called "micromounts") or systematic minerals, the highest value is placed on a well-documented specimen with analytically confirmed identity. The presence of well-formed, even if tiny, crystals and a rich association of co-occurring minerals on the same sample enhance its attractiveness. ## Popular Localities The only source of specimens is the type locality – the Snezhnoye deposit in Yakutia, Russia. Material from this location is extremely difficult to obtain and appears on the collector's market sporadically.

Care and storage

## Cleaning Due to the extreme rarity and small size of the crystals, mechanical cleaning of specimens is usually neither necessary nor recommended. If there is a need to remove loose contaminants, compressed air (from a safe distance) or a very soft brush can be used. ## What to Avoid Avoid contact with acids, which can damage the mineral. Do not subject it to ultrasonic cleaning or steam cleaners. Store away from chemicals and extreme temperatures. ## Storage Pertsevite-(OH) specimens are typically microscopic and should be stored in specialized micromount boxes, protecting them from dust, moisture, and mechanical damage. Avoid exposure to conditions that could cause physical or chemical damage to the delicate crystals.

Sources

IMA Mineral List (CNMNC)