Fluor-dravite

Chemical formula: NaMg₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F

Fluor-dravite is a rare mineral from the tourmaline group, being the fluorine analogue of dravite, distinguished by its occurrence in magnesium-rich metamorphic rocks.

## Characteristics Fluor-dravite is a mineral belonging to the tourmaline group. It is the fluorine analogue of dravite, meaning that in its chemical structure, fluorine dominates over the hydroxyl group (OH) at a specific site. It typically forms prismatic, elongated crystals with a characteristic rounded triangular cross-section, typical of tourmalines. Crystals often exhibit vertical striations on the prism faces. Its appearance is very similar to other tourmalines, especially dravite and schorl, and definitive identification requires advanced analytical methods. ## Physical Properties Fluor-dravite is characterized by significant hardness, typical of tourmalines, measuring approximately 7 on the Mohs scale. It has a vitreous luster. It is a brittle mineral with an uneven or conchoidal fracture. Its density is similar to other magnesium tourmalines, around 3.03 g/cm³. ## Colors and Varieties Observed colors of fluor-dravite range from dark green, bluish-green to almost black. The color is often unevenly distributed, forming color zones within a single crystal. No distinct commercial or color varieties of this mineral are recognized, and its name refers strictly to its chemical composition. ## History and Name The name "fluor-dravite" directly indicates its chemical composition – it is a dravite in which fluorine is the dominant anion at a specific site in the crystal structure. It was formally described as a new mineral species and approved by the International Mineralogical Association (IMA) in 2010. Its discovery is relatively recent compared to more well-known members of the tourmaline group. ## Applications Due to its rarity, fluor-dravite has no industrial applications. It is of purely scientific significance, as an indicator of specific geochemical conditions, and collector's interest, being sought after by advanced collectors of tourmaline group minerals and rare minerals.

Properties

Mohs hardness: 7
Luster: Vitreous
Streak: White
Density: 3.03
Cleavage: None
Fracture: Uneven, Conchoidal
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identifying fluor-dravite in the field or based on visual characteristics is practically impossible. Its appearance is identical to other dark tourmalines, such as schorl or dravite. The characteristic triangular cross-section of the crystal and vertical striations, typical of tourmalines, are important clues that one is dealing with a mineral from this group. However, definitive identification requires advanced chemical analyses (e.g., electron microprobe) or spectroscopic methods to confirm the dominance of fluorine over the OH group. ## Distinguishing from Similar Minerals Fluor-dravite is most often confused with dravite and schorl. It differs from dravite by the dominance of fluorine over the hydroxyl group, and from schorl (iron tourmaline) by the dominance of magnesium over iron. Distinguishing it from these minerals without specialized equipment is impossible. It can also be confused with hornblende, from which it differs by greater hardness and the lack of typical amphibole cleavage. ## Crystal Forms Fluor-dravite forms well-developed, columnar (prismatic) crystals, typical of tourmalines. Crystals are often terminated by complex pyramid and pinacoid faces. A characteristic feature is the cross-section of the crystals, which has a spherical triangular shape. It also occurs in radial aggregates or as inclusions in other minerals.

Geological environment

## Genesis Fluor-dravite forms under conditions of regional metamorphism, in rocks rich in magnesium and boron, with the presence of fluorine in the crystallization environment. Its formation is associated with rocks such as dolomitic marbles, skarns, and some metamorphic schists that have been subjected to hydrothermal solutions saturated with boron and fluorine. ## Mineral Associations This mineral often co-occurs with other minerals typical of metamorphic rocks and skarns. The most common associations include: calcite, dolomite, quartz, phlogopite, tremolite, diopside, as well as other minerals from the tourmaline group. ## Localities As a rare mineral, fluor-dravite has been identified in only a few places worldwide. The type locality (place of first description) is the Crusin quarry, near San Piero in Campo on Elba Island, Italy. Other confirmed occurrences include: Chitwood in St. Lawrence County (New York, USA) and some localities in the Czech Republic (near Nedvědice).

Rarity

Rare

For collectors

## Quality Criteria The most valued fluor-dravite specimens by collectors are those that present well-formed, terminated, and undamaged crystals with a distinct, prismatic habit. Intense, though rare, greenish or bluish color enhances their attractiveness. Specimens on a rock matrix, showing association with other minerals (e.g., with white calcite), are generally more highly valued than single, loose crystals. However, a key factor in value is the analytical confirmation that a given specimen is indeed fluor-dravite, and not a more common dravite or schorl. ## Popular Localities Specimens from the type locality, Elba, Italy, are of particular value to collectors specializing in rare minerals and systematics. Specimens from St. Lawrence County, USA, are also known and sought after in collecting circles.

Care and storage

## Cleaning It is recommended to clean specimens using a soft brush and distilled water. A small amount of neutral soap can be used, but it must be thoroughly rinsed off. Due to its hardness, it is relatively resistant to mechanical damage during cleaning. ## What to Avoid Avoid contact with strong acids, especially hydrofluoric acid. Although it is a relatively stable mineral, rapid temperature changes, which could cause internal fractures, are not recommended. Prolonged exposure to intense sunlight could theoretically affect the color of some specimens, although this is not a documented problem for this particular mineral. ## Storage Fluor-dravite specimens should be stored in a way that protects them from dust and scratches by harder minerals (e.g., corundum, diamond). They can be displayed in enclosed showcases. Due to its brittleness, avoid placing them in areas prone to shocks or falls.

Sources

IMA Mineral List (CNMNC)