Tungstenite

Chemical formula: W<sup>4+</sup>S<sup>2-</sup><sub>2</sub>

Tungstenite is a rare tungsten sulfide mineral, characterized by a metallic luster, lead-gray color, and lamellar structure.

## Characteristics Tungstenite is a tungsten sulfide (WS₂), the natural analogue of synthetic tungsten disulfide. It usually forms fine-grained or lamellar aggregates, as well as thin coatings. It rarely occurs as small, hexagonal, tabular crystals. Its appearance is very similar to molybdenite and graphite. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2.5. It has a metallic luster and is opaque. It is a very dense mineral, with a specific gravity of about 7.4 g/cm³, which clearly distinguishes it from similar minerals. It feels greasy to the touch. ## Colors and Varieties Tungstenite is lead-gray to dark gray or black. There are no distinct color or commercial varieties. ## History and Name The mineral's name, given in 1917, directly refers to its chemical composition – a high tungsten content. It was first described from specimens found in the Emma Mine in the Little Cottonwood District, Utah (USA). ## Uses As a mineral, tungstenite is primarily of scientific and collector's interest. Its synthetic counterpart is widely used as a high-performance dry lubricant, especially in vacuum and high-temperature conditions.

Properties

Mohs hardness
2.5
Luster
Metallic
Streak
Dark-gray
Density
7.4
Cleavage
Perfect on {0001}
Transparency
Opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Key diagnostic features include its lead-gray color, strong metallic luster, very low hardness (can be scratched with a fingernail), and lamellar or scaly habit. Its very high density is also characteristic. ## Distinguishing from Similar Minerals Tungstenite is most often confused with molybdenite and graphite. It is distinguished from graphite by its significantly higher density and a slightly brighter, more metallic hue. Molybdenite has a similar appearance but is lighter (density approx. 4.7 g/cm³) and often exhibits a bluish tint, which is absent in tungstenite. Final differentiation requires laboratory tests (e.g., EDS). ## Crystal Forms Crystals are rare, hexagonal, and in the form of small, thin tablets. It is most commonly found as lamellar or scaly aggregates or as fine-grained masses.

Geological environment

## Genesis It is a hydrothermal mineral, forming at low temperatures. It occurs in ore veins and in metasomatic alteration zones. ## Mineral Associations It co-occurs with minerals such as pyrite, quartz, siderite, scheelite, and especially molybdenite. ## Localities Major worldwide localities include the Emma Mine in Utah (USA), where it was discovered, as well as some deposits in Sweden (e.g., Bispberg), Japan (Kuga Mine, Yamaguchi Prefecture), and Russia.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, though usually microscopic, hexagonal crystals. Rich lamellar aggregates on a contrasting rock matrix are also attractive. ## Popular Localities Specimens of historical significance come from the type locality in Utah, USA.

Care and storage

## Cleaning Due to its high softness and perfect cleavage, tungstenite should only be dry-cleaned, using a soft brush to remove dust. Water and any chemical agents should be avoided. ## What to Avoid Avoid contact with harder minerals that could scratch it. It is sensitive to mechanical pressure, which can cause lamellae to separate. Ultrasonic cleaners or strong air jets should not be used. ## Storage Tungstenite specimens are best stored in separate, padded boxes to protect them from scratches and mechanical damage.

External references

Sources

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