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The Mineral millerite

Millerite on Stilpnomelane

Millerite is known for its interesting crystal habit of slender brassy crystal growths and hair-like tufts. It frequently forms inside geodes and vugs where it has the room to develop its interesting crystals. Millerite was named in honor of William Hallowes Miller (1801 – 1880), a prominent Welsh mineralogist  responsible for laying the foundations of modern crystallography. The miller indices relating to crystallography are named after him.

Chemical Formula

NiS

Color

Metallic yellow, bronze, silvery-gray. May display an iridescent tarnish.

Crystal System

Hexagonal

Properties

Streak
Greenish black
Hardness
3 - 3.5
Transparency
Opaque
Specific Gravity
5.3 - 5.5
Luster
Metallic
Cleavage
1,2
Fracture
Splintery, uneven
Tenacity
Brittle. Slender crystals slightly flexible and elastic.

Crystal Habits

In dense needle growths and hair-like tufts, acicular groups of thin needles, capillary, radiating, as botryoidal masses of needles, in thick radiating veins, plumose, and massive.

3D Crystal Atlas

Additional Information

Composition
Nickel sulfide, sometimes with iron, copper, and cobalt
In Group
Sulfides; Simple Sulfides
Striking Features
Crystal habit and mode of occurrence
Environment
In hydrothermal replacement deposits, nickel-rich orebodies, and in limestone and dolomite pockets and cavities.
Rock Type
Sedimentary, Metamorphic

Uses

Millerite is an ore of nickel. It is an uncommon mineral and good crystals are highly valued by collectors.

Noteworthy Localities

Germany contains many old and classic localities for Millerite, with the best being the Friedrich Mine, Wissen, Siegerland (unusually thick crystals) and Ramsbeck, North Rhine-Westphalia. Other worldwide localities include the Glamorgan area, Wales, UK; Kladno, Bohemia, Czech Republic; the Perseverance Mine, Leinster, Leonora Shire, Western Australia; and the Pafuri Nickel Deposit, Limpopo Province, South Africa.

In the U.S., dense Millerite needles in geodes are well-known at the Route 27 Roadcut, Halls Gap, Lincoln Co., Kentucky. Highly aesthetic acicular sprays in vugs with Stilpnomelane were found in the Sterling Mine, Antwerp, Jefferson Co., New York, which is another classic locality for this mineral. Thick Millerite mats in geodes come from Ollie, Keokuk Co., Iowa; and Millerite embedded inside Calcite crystals from Keokuk, Lee Co., Iowa. Botryoidal Millerite aggregates formed from radial needles have come from the Gap Mine, Lancaster Co., Pennsylvania; and aesthetic sprays from Estabrook Park in the city of Milwaukee, Milwaukee Co., Wisconsin. Hairy Millerite masses have been found at the Wallace Quarry, Pigeon, Huron Co., Michigan; and tree-like formations of densely interconnected crystals create an aesthetic form of this mineral at the Meikle Mine, Elko Co., Nevada.

In Canada, radiating Millerite balls and veins have come from the Thompson Mine, Manitoba; and massive Millerite with Chalcopyrite was mined in Levack Township, Sudbury, Ontario.

Common Mineral Associations

Calcite, Chalcopyrite, Siderite, Quartz, Hematite


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