Vanadio-oxy-chromium-dravite
Chemical formula: NaV³⁺₃(Cr³⁺₄Mg₂)(Si₆O₁₈)(BO₃)₃(OH)₃O
Vanadio-oxy-chrom-dravite is a very rare mineral from the tourmaline group, distinguished by its unique chemical composition with vanadium and chromium.
Properties
- Mohs hardness
- 7.5
- Color
- Emerald green
- Luster
- Vitreous
- Streak
- Pale green
- Density
- 3.3
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Translucent in thin fragments, Opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Identification of this mineral is almost exclusively possible using advanced analytical methods, such as energy-dispersive spectroscopy (EDS/WDS) to confirm its unique chemical composition (presence of Na, V, Cr, Mg, Si, B). Visually, it is a dark green to black tourmaline with a vitreous luster. ## Distinguishing from similar minerals It can be confused with other dark tourmalines, such as schorl, dravite, chromo-alumino-povondraite, or vanadio-dravite. Certain differentiation requires chemical analysis, as physical characteristics (color, hardness, habit) are very similar within the entire group. ## Crystal forms It forms columnar, prismatic crystals with a trigonal cross-section, often terminated by a pyramid. They occur as single, euhedral (well-formed) crystals or in the form of radial aggregates.
Geological environment
## Genesis Vanadio-oxy-chrom-dravite forms under specific conditions of low-grade metamorphism. It occurs in quartz-calcite veins cutting sericite-chlorite schists with graphite. Its formation is associated with the presence of primary sedimentary rocks rich in organic matter and heavy minerals, which supplied vanadium and chromium. ## Mineral associations This mineral co-occurs with quartz, calcite, chlorite, muscovite (sericite variety), titanite, rutile, apatite, pyrite, and other tourmalines, such as dravite and vanadio-dravite. ## Localities The only confirmed occurrence of this mineral in the world (type locality) is an abandoned quarry near the village of Crni Vrh in the Pohorje Mountains in Slovenia.
Rarity
Extremely rare
For collectors
## Quality criteria The collector's appeal of vanadio-oxy-chrom-dravite specimens primarily depends on the quality and development of the crystals. The most valued are single, sharply terminated, lustrous crystals with a distinct prismatic form, set on a contrasting matrix (e.g., white quartz or calcite). The size of the crystals, even if exceeding 1 mm, significantly increases the value of the specimen. The aesthetics of the entire "micromount" are also important. ## Popular localities The only source of specimens is the type locality in Slovenia. Material from this location is extremely limited, and finding new material is practically impossible, making each specimen unique.
Care and storage
## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the brittleness and small size of the crystals, mechanical cleaning, including brushes, should be avoided. Contact with water or other liquids is not recommended. ## What to avoid Avoid contact with chemicals, especially acids, which can damage the mineral. The crystals are brittle, so they should be protected from impacts and vibrations. They should not be subjected to ultrasonic cleaning. ## Storage Specimens of vanadio-oxy-chrom-dravite, usually in the form of "micromounts," should be stored in dedicated, sealed perky boxes that protect them from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight, although there is no evidence of fading.