Orthopinakiolite

Chemical formula: Mg₂Mn₃+O₂(BO₃)

Orthopinakiolite is a rare, black borate mineral of the orthopinakiolite group, found as elongated, prismatic crystals.

## Characteristics Orthopinakiolite is a rare borate mineral belonging to the orthopinakiolite group. It forms characteristic, elongated, prismatic or bladed crystals, often aggregated into radial or chaotic clusters. Its color is uniformly black, and its luster is metallic, giving it an appearance similar to some manganese oxides. ## Physical Properties This mineral is characterized by a hardness of 6 on the Mohs scale. It is opaque, and its density is approximately 3.94 g/cm³. The luster is described as metallic. ## Colors and Varieties Orthopinakiolite occurs exclusively in black. No colored or commercial varieties are known. ## History and Name The mineral's name refers to its orthorhombic crystal system and its similarity to pinakiolite. It was first described in 1960 based on specimens found in the Långban mine in Sweden, which is its type locality. ## Uses Orthopinakiolite has no industrial applications. It is of scientific and collector's interest only, as a rare and well-formed mineral.

Properties

Mohs hardness: 6
Luster: Metallic
Streak: Black
Density: 3.935
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Orthopinakiolite can be identified by its black color, metallic luster, and characteristic form of elongated, prismatic crystals, often forming radial aggregates. Hardness (6 on the Mohs scale) is also a helpful feature. ## Distinguishing from Similar Minerals It can be confused with other black, acicular manganese minerals, such as pyrolusite or hollandite. Differentiation often requires advanced research methods, such as X-ray diffraction (XRD), although crystal form and hardness can be helpful in preliminary identification. ## Crystal Forms Crystals are typically strongly elongated in one direction, forming prismatic, acicular, or bladed shapes. They often occur as radial or haphazardly arranged aggregates embedded in the host rock.

Geological environment

## Genesis Orthopinakiolite is a metamorphic mineral. It forms as a result of contact metamorphism of iron and manganese ore deposits in skarns and carbonate rocks (dolomitic marbles). ## Mineral Associations This mineral co-occurs with other minerals typical of metamorphosed manganese deposits, such as magnetite, hausmannite, tephroite, ludwigite, and other rare borates. ## Localities The most important and classic occurrence of orthopinakiolite is its type locality - the Långban mine in the Värmland region of Sweden. This site is known for the occurrence of many rare and unique minerals. Beyond Sweden, its presence has been reported in several other locations worldwide, but specimens from there are much rarer.

Rarity

Very rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp, and undamaged crystals, forming aesthetic, radial aggregates. Contrast with a light host rock (e.g., white marble) significantly enhances the visual appeal and value of the specimen. The size of the crystals and the entire aggregate is also an important factor. ## Popular Localities By far the most sought-after and commonly found specimens on the collector's market come from the Långban mine in Sweden. This is the classic and most important locality for this mineral.

Care and storage

## Cleaning Orthopinakiolite specimens should be cleaned very carefully, using a soft brush to remove dust. Compressed air from a safe distance is permissible. Avoid washing in water, especially with detergents. ## What to Avoid Avoid contact with acids and other chemicals that can damage the mineral's surface. Brittle crystals are sensitive to impacts and vibrations. Do not subject it to ultrasonic cleaning. ## Storage Due to their fragility and rarity, collector specimens of orthopinakiolite are best stored in "membrane box" type display cases or in foam-lined mineral boxes to protect them from mechanical damage and dust.

External references

https://www.mindat.org/min-3030.html