Vanadio-oxy-dravite

Chemical formula: NaV₃+₃(Al₄Mg₂)(Si₆O₁₈)(BO₃)₃(OH)₃O

Vanadio-oxy-dravite is an extremely rare, black mineral from the tourmaline group, distinguished by its high vanadium content and known from only one locality in the world.

## Characteristics Vanadio-oxy-dravite is a member of the tourmaline group, approved as a distinct mineral species in 2012. It forms black, opaque, short prismatic crystals with a characteristic triangular cross-section typical of tourmalines. It exhibits a submetallic luster, which distinguishes it from the more typical vitreous luster of most tourmalines. It occurs as single crystals embedded in the host rock or in small, radial aggregates. ## Physical Properties This mineral is characterized by significant hardness, reaching 7.5 on the Mohs scale, which is typical for tourmalines. Its density is calculated at 3.26 g/cm³. It shows no cleavage, and its fracture is uneven to conchoidal. It is opaque in larger fragments but becomes translucent and shows a greenish tint in very thin splinters. ## Colors and Varieties The only known color of vanadio-oxy-dravite is black. No color varieties or commercial varieties have been described. ## History and Name The mineral's name directly reflects its chemical composition: the "vanadio-" prefix indicates the dominance of vanadium at a specific site in the crystal structure, "oxy-" indicates the dominance of oxygen over hydroxyl groups, and "dravite" refers to its structural kinship with dravite, another mineral from the tourmaline group. It was discovered in the Pereval marble quarry in the Slyudyanka complex near Lake Baikal in Russia, which remains its only known locality. ## Uses Vanadio-oxy-dravite has no industrial applications. Its significance is purely scientific and collectible, being an object of desire among specialists collecting rare minerals and type specimens (originating from the type locality).

Properties

Mohs hardness: 7.5
Luster: Submetallic
Streak: Grayish green
Density: 3.26
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque, Translucent in thin fragments
Crystal system: Trigonal

Diagnostic features

## Identification Helpful identification features include black color, submetallic luster, high hardness (7.5), and the typical crystal habit of tourmalines. However, a key clue is the locality – this mineral comes exclusively from the Slyudyanka complex in Russia. A grayish-green streak is an important distinguishing feature. Final and certain identification requires advanced chemical analyses (e.g., EDS) to confirm the dominance of vanadium and oxygen in the composition. ## Distinguishing from Similar Minerals Vanadio-oxy-dravite is visually indistinguishable from other black tourmalines, such as schorl, dravite, or the related vanadio-dravite, without specialized equipment. Schorl, the most common black tourmaline, usually has a lighter, white or gray streak. It can only be distinguished from vanadio-dravite, with which it co-occurs, by detailed structural and chemical analysis. ## Crystal Forms It forms short, prismatic crystals with a triangular outline. Crystal terminations are usually flat or poorly developed. It occurs as single crystals embedded in the matrix or as small, radially divergent aggregates.

Geological environment

## Genesis This mineral forms under specific conditions of contact metamorphism. Its formation environment is metasomatic rocks (skarns) formed at the contact of magmatic intrusions with carbonate rocks (marbles). It requires the presence of boron- and vanadium-rich fluids. ## Mineral Associations It most often co-occurs with calcite, diopside, titanite, pyrite, and other vanadium-rich tourmalines, such as vanadio-dravite. ## Localities The only confirmed occurrence of vanadio-oxy-dravite in the world is the Pereval marble quarry, located in the Slyudyanka geological complex, in the Irkutsk Oblast near Lake Baikal in Russia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria As an extremely rare mineral, the main criterion for value is its mere presence in a collection. Specimens with well-formed, sharp, and lustrous crystals are most highly prized, even if they are small (millimeter-sized). The attractiveness of a specimen is enhanced by its placement on a contrasting, light matrix (e.g., white calcite), which highlights the black crystals. Precise documentation confirming its origin from the type locality is also important. ## Popular Localities All known and commercially available specimens originate from a single location – the Pereval quarry in Russia. This is the only source of this mineral.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its hardness (7.5), the mineral itself is scratch-resistant, but it often occurs on a more delicate calcite matrix. Ultrasonic cleaners are not recommended, as they can cause cracks or separation of crystals from the substrate. ## What to Avoid Avoid contact with strong acids, which can damage co-occurring calcite. The mineral is stable, but extreme and sudden temperature changes should be avoided. ## Storage Store in separate, lined boxes to protect specimens from dust and mechanical damage. Due to its rarity and scientific value, each specimen should be precisely labeled with its name and locality.

Sources

IMA Mineral List (CNMNC)