Khesinite
Chemical formula: Ca₄(Mg₂Fe³⁺₁₀)O₄(Fe³⁺₁₀Si₂)O₃₆
Dark brown to black, rare mineral of the aenigmatite group, found in calciphyres in the Lake Baikal region of Russia.
Properties
- Mohs hardness
- 6
- Color
- Black to dark brown
- Luster
- Metallic, Sub-Metallic
- Streak
- Brown
- Density
- 4.097
- Cleavage
- None
- Fracture
- Irregular/Uneven
- Transparency
- Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification Amateur identification of khesinite is practically impossible. It requires advanced analytical methods, such as chemical analysis (EDS/WDS) and X-ray diffraction (XRD). It is distinguished by its black color, metallic luster, and co-occurrence with other minerals within calciphyres. ## Distinguishing from Similar Minerals It can be confused with other black, opaque minerals from the aenigmatite group (e.g., aenigmatite, krinovite) or other iron and titanium oxides (e.g., ilmenite). Differentiation requires specialized laboratory tests to determine the exact chemical composition and crystal structure. ## Crystal Forms Khesinite forms small, poorly formed (subhedral) crystals with a tabular or short-prismatic habit. It most often occurs as granular aggregates, embedded in the rock.
Geological environment
## Genesis Khesinite forms under conditions of high-grade contact metamorphism (sanidinite facies). It forms in calciphyres – metamorphic rocks resulting from the alteration of impure limestones or marls, in contact with basic rock intrusions. ## Mineral Associations This mineral co-occurs with minerals such as: calcite, diopside, forsterite, monticellite, perovskite, titanite, spinel, apatite, as well as rarer minerals like tazheranite, sharyginite, and lakargiite. ## Localities The only confirmed locality of khesinite in the world is its type locality: the Tazheran (Tazheranskoye) deposit in the Tazheran massif, near Lake Baikal, in the Irkutsk Oblast, Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria As a mineral of primarily scientific importance, specimens with the best-formed and largest crystals, whose identification has been analytically confirmed, are most valued. Rich association with other rare minerals from this locality is also crucial. ## Popular Localities The only source of khesinite specimens is the Tazheran massif in Russia. Collector material is extremely rare and practically unavailable on the open market.
Care and storage
## Cleaning Due to its brittleness and small crystal size, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water or chemicals is inadvisable due to a lack of data on its reactivity. ## What to Avoid Avoid contact with acids and other chemicals. The mineral is brittle, so it should be protected from impacts, scratching, and vibrations. It should not be subjected to ultrasonic cleaning. ## Storage Khesinite specimens, being rare and typically small, should be stored in stable conditions, in enclosed "micromount" boxes, protecting them from dust and mechanical damage.