Uvite

Chemical formula: CaMg₃(Al₅Mg)(Si₆O₁₈)(BO₃)₃(OH)₃OH

Uvite is a rare mineral from the tourmaline group, valued for its well-formed, often dark green or brown crystals with a characteristic trigonal habit.

## Characteristics Uvite is a mineral belonging to the complex tourmaline group, distinguished within this group by the dominance of calcium (Ca) in its structure. It forms well-developed, prismatic crystals with a cross-section characteristic of tourmalines, shaped like a rounded triangle. Crystals are often terminated by flat or complex faces. Typical specimens have an intense, dark color, ranging from green through brown to almost black, although lighter shades also occur. ## Physical Properties Uvite is characterized by significant hardness, measuring 7.5 on the Mohs scale, which makes it resistant to scratching. Its luster is vitreous, and depending on the purity and thickness of the crystal, it can range from transparent to almost opaque. The density of uvite ranges from 3.00 to 3.21 g/cm³. ## Colors and Varieties The dominant colors of uvite are dark green, brown, and reddish-brown, often so intense that the mineral appears black. Colorless, yellow, or pink specimens are rarer. Some crystals exhibit color zoning, where different shades are arranged in layers along the growth axis of the crystal. Some dark green, chromium-rich varieties are sometimes referred to by the trade name "chrome tourmaline," although this name is not exclusively reserved for uvite. ## History and Name The name "uvite" comes from the Uva Province in Sri Lanka, where this mineral was first identified. It was described as a distinct mineral species in 1929 by mineralogist W.A. Kuntze. As a member of the tourmaline group, it shares a long and complex classification history with them. ## Uses Due to its rarity and often dark color, uvite has limited use in jewelry. The purest and most colorfully interesting crystals are sometimes faceted for collectors. Primarily, however, uvite is a valued and sought-after collector's mineral, and well-formed crystals are an adornment to mineralogical collections.

Properties

Mohs hardness: 7.5
Luster: Vitreous
Streak: White
Density: 3.00-3.21
Cleavage: None
Fracture: Uneven, Conchoidal
Transparency: Transparent to opaque
Crystal system: Trigonal

Diagnostic features

## Identification A key diagnostic feature of uvite, as with other tourmalines, is the characteristic habit of its crystals: elongated prisms with a cross-section that is a rounded triangle. Strong dichroism (change in color depending on the direction of observation) is also typical. A hardness of 7.5 on the Mohs scale distinguishes it from many similarly appearing minerals. ## Distinguishing from Similar Minerals Uvite is difficult to distinguish from other dark tourmalines (e.g., Schorl, Dravite) without advanced chemical analysis. Dravite often occurs in similar metamorphic environments. Schorl is usually black and opaque. From other minerals, such as Smoky Quartz or Epidote, it is primarily distinguished by its characteristic crystal cross-section and higher hardness. ## Crystal Forms Uvite forms prismatic crystals, often short and thick, in contrast to the more acicular forms of some other tourmalines. The cross-section is typically triangular with convex sides. Vertical striations are often visible on the prism faces. It also occurs in the form of radial aggregates or granular masses.

Geological environment

## Genesis Uvite is a typical mineral of metamorphic rocks, rich in magnesium and calcium, such as marbles, skarns, and serpentinites. It forms under conditions of contact or regional metamorphism. It can also crystallize in granitic pegmatites, although this is a rarer environment for this particular member of the tourmaline group. ## Mineral Associations Minerals commonly associated with uvite often include Calcite, Dolomite, Diopside, Tremolite, Phlogopite, Spinel, Apatite, and other tourmalines, such as Dravite. ## Localities The most important and historical localities for uvite are Uva Province in Sri Lanka (type locality). Beautiful, well-formed crystals come from Brumado, Brazil, where they occur in association with Magnesite. Other known localities include the Zillertal Valley in Austria, regions in Pakistan and Afghanistan, as well as some localities in the USA (New York and California) and Canada (Quebec).

Rarity

Not very common

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, sharp crystals with distinct terminations. Transparency and intense, but not too dark, color are highly prized – especially vibrant shades of green and reddish-brown. Specimens on matrix, particularly in contrasting arrangements with white Calcite or Magnesite (like those from Brumado), fetch the highest prices. Crystal size also significantly increases the value of a specimen. ## Popular Localities The best specimens in the world are considered to be those from the Pedra Preta mine in Brumado (Bahia, Brazil), which yield magnificent green and brown crystals on white Magnesite. Classic, though often smaller, specimens come from Sri Lanka and Austria. In recent years, attractive specimens from Pakistan and Afghanistan have also appeared on the market.

Care and storage

## Cleaning Uvite specimens can be safely cleaned using a soft brush and lukewarm water with a mild soap. After washing, they should be thoroughly rinsed with distilled water to avoid leaving deposits, and then gently dried. ## What to Avoid Avoid cleaning with ultrasonic and steam cleaners, as sudden temperature changes and vibrations can cause cracks, especially in crystals with internal inclusions. Uvite is chemically resistant, but contact with strong acids, especially hydrofluoric acid, should be avoided. Prolonged exposure to intense sunlight can theoretically cause some colored varieties to fade. ## Storage Uvite is a hard but brittle mineral. It should be stored in a way that prevents impacts or contact with harder minerals (like diamond, corundum) that could scratch it. It is best to keep it in separate display boxes or on stands, away from specimens that it could scratch itself (e.g., Fluorite, Calcite).

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FFluor-uvite