Scheelite

CaWO4

Bispbergs klack

Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten (W). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. Scheelite has been synthesized via the Czochralski process; the material produced may be used to imitate diamond, as it has a similar dispersion and other optical properties. Scheelite fluoresces under short-wave ultraviolet light, with the color ranging from blue to white, which is a distinctive feature that aids in its identification.

Properties

Scheelite crystallizes in the tetragonal system. It forms transparent to opaque crystals that are typically colorless or pale shades of yellow, orange, or brown. The mineral has a Mohs hardness of about 4.5 to 5 and a specific gravity of approximately 6.0 to 6.1. It exhibits high dispersion, which can give cut stones a fire similar to that of diamond. One of the most striking properties of Scheelite is its ability to fluoresce under ultraviolet light, a characteristic that is utilized by geologists and miners to locate and identify the mineral.

Occurrence

Scheelite is found in igneous and metamorphic rocks and particularly in skarn deposits, where it is formed by the action of silica-rich fluids on calcium-bearing rocks in the presence of tungsten. It is often associated with minerals such as quartz, calcite, and garnet. Major producers of scheelite include China, Russia, and Bolivia, with significant deposits also found in Austria, Korea, and Portugal.

Uses

The primary use of scheelite is as a source of tungsten, a metal critical for the manufacture of hard metals and alloys, electrical contacts, high-speed steel, and other applications requiring materials with high melting points, strength, and hardness. Tungsten extracted from scheelite is essential for the production of the filament used in incandescent light bulbs, although this application has diminished with the advent of LED lighting.

Synthesis and Imitation

Scheelite can be synthesized for various purposes, including research and the creation of gemstone imitations. Synthetic scheelite is produced using the Czochralski process, which allows for the growth of large, high-quality crystals that can be cut into gems. These synthetic versions are used to imitate more expensive gemstones like diamond due to scheelite's similar optical properties, such as dispersion.

Environmental and Health Concerns

The mining and processing of scheelite can lead to environmental degradation if not managed properly. Tungsten mining operations can result in the contamination of water sources with heavy metals, leading to potential health risks for local communities. Proper management and remediation efforts are essential to minimize these impacts.

See Also

• Tungsten
• Mineral
• Skarn
• Gemstone
• Fluorescence

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