Pinakiolite
Chemical formula: (Mg,Mn²⁺)₂(Mn³⁺,Sb⁵⁺)O₂(BO₃)
Pinakiolite is a rare magnesium and manganese borate, forming characteristic, elongated, almost black crystals with a metallic luster.
Properties
- Mohs hardness
- 6
- Color
- Black; deep reddish brown in transmitted light
- Luster
- Metallic
- Streak
- Brown-gray
- Density
- 3.88
- Cleavage
- On {010}.
- Fracture
- Uneven
- Transparency
- Translucent,Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Pinakiolite can be identified by its characteristic appearance: black, highly lustrous, elongated crystals with a bladed habit, often forming radial aggregates. Perfect cleavage in one direction and high density are also important diagnostic features. ## Distinguishing from Similar Minerals Pinakiolite is sometimes confused with other black, elongated minerals from manganese skarns, such as ludwigite, tourmaline (schorl), or pyroxenes. It is often distinguished from ludwigite by a more metallic luster and slightly different crystal forms. It differs from schorl by its habit (bladed, not prismatic with a triangular cross-section) and significantly higher density. Pyroxenes usually have a weaker luster and different cleavage. ## Crystal Forms Crystals are monoclinic, but often appear orthorhombic (pseudo-orthorhombic). They have the form of flattened, elongated blades or needles. They occur as single crystals embedded in the host rock or as radial, stellate, and chaotic aggregates.
Geological environment
## Genesis Pinakiolite is a metamorphic mineral, formed as a result of contact metamorphism of iron and manganese ore deposits in skarns that have been modified by metasomatic processes involving boron. It forms at high temperatures in the presence of magnesium, manganese, and boron. ## Mineral Associations It most commonly co-occurs with other minerals typical of manganese skarns from Långban, such as hausmannite, tephroite, berzeliite, manganostibite, magnetite, dolomite, and calcite. ## Localities The most important and classic locality for pinakiolite in the world is the Långban mine in the Värmland region of Sweden, from where the best specimens originate. It is also known from several other geologically similar localities, such as the Jakobsberg mine (also in Sweden) and the Tary-Ekan deposit in Tajikistan.
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, sharp, highly lustrous crystals, forming aesthetic, radial aggregates on a contrasting background (e.g., on white calcite). The size of the crystals and entire aggregates also significantly affects the value. Specimens from the classic Långban locality are particularly sought after. ## Popular Localities By far the most desirable and historically important locality is Långban in Sweden. Specimens from there are considered exemplary for this species and fetch the highest prices on the collector's market.
Care and storage
## Cleaning Pinakiolite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, compressed air can be used. Avoid washing in water, especially with detergents, as moisture can penetrate cleavage planes. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage the mineral. Pinakiolite is brittle, so it should be protected from impacts and falls. It does not require special protection from light, but extreme temperature changes should be avoided. ## Storage It is best to store specimens in closed display boxes, lined with soft material, to prevent mechanical damage and dust accumulation. Due to its perfect cleavage, other minerals should not be placed on top of it.