Millerite

Millerite structure

Millerite-44389

Calcite-millerite association

Millerite is a nickel sulfide mineral with the chemical formula NiS. It is known for its distinctive needle-like crystals and is named after William Hallowes Miller, a British mineralogist who first described the mineral in 1845. Millerite is an important ore of nickel and is found in hydrothermal veins, often associated with other nickel-bearing minerals such as pentlandite. It can also occur in meteorites and as a secondary mineral in nickel-rich serpentinites.

Properties

Millerite forms in trigonal crystal system, exhibiting long, slender, and often radiating needles. These needles can be bright yellow to brass-colored, which makes millerite easily distinguishable from other minerals. The hardness of millerite on the Mohs scale of mineral hardness is 3 to 3.5, making it relatively soft. Its specific gravity is about 5.3 to 5.5, which is considered high, indicating a dense mineral.

Occurrence

Millerite is commonly found in hydrothermal vents and sedimentary rocks, particularly in limestone where it fills cavities and fractures. It is also present in meteorites and ultramafic rocks, and is often associated with minerals such as chalcopyrite, pyrite, and pentlandite. Major deposits of millerite have been found in Germany, Wales, South Africa, and the United States, particularly in the states of Kentucky, Missouri, and Wisconsin.

Uses

The primary use of millerite is as an ore of nickel. Nickel is a significant industrial metal used in stainless steel production, batteries, and various alloys. Despite its relatively rare occurrence compared to other nickel ores, millerite is valued for its high nickel content.

Environmental and Health Concerns

Handling millerite, especially in powdered form, requires caution due to its nickel content. Nickel compounds can be toxic and carcinogenic, posing risks to human health upon prolonged exposure. Environmental concerns also arise from mining activities, which can lead to habitat destruction and water pollution.

See Also

• Nickel
• Mineral
• Ore
• Hydrothermal vent

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