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The Mineral enargite

Lustrous Striated Enargite Crystal

Enargite is a sulfosalt mineral that is an import ore of copper. Crystals are sometimes coated with a thin layer of Pyrite crystals, giving it a yellow appearance. Enargite is dimorphous with the mineral Luzonite, which forms in tetragonal crystals. Luzonite and Enargite sometimes form together in single altering crystals with different symmetry and cleavage habits.

Enargite is named for the Greek word enargos, meaning "distinct, in reference to its distinctive perfect cleavage.

Chemical Formula

Cu3AsS4

Color

Steel Gray to black. May also be iridescent with a dark red or violet metallic film, or may have a dull gray tarnish.

Crystal System

Orthorhombic

Properties

Streak
Dark gray to black
Hardness
3
Transparency
Opaque
Specific Gravity
4.4 - 4.5
Luster
Metallic
Cleavage
1,1 ; 2,2
Fracture
Uneven
Tenacity
Brittle

Crystal Habits

In prismatic and tabular crystals, with flattened, rectangular terminations or with chisel-tipped terminations that may be somewhat rounded. Crystals may be individual, interconnected, in flowering groups of crystals, and in rounded crystal masses. Also columnar, bladed, drusy, grainy, and massive. Crystals are often deeply striated.

3D Crystal Atlas

Additional Information

Composition
Copper arsenic sulfide
In Group
Sulfides; Sulfosalts
Striking Features
Color, crystal habits, and perfect cleavage
Environment
In low to moderate grade hydrothermal and epithermal vein deposits.
Rock Type
Sedimentary, Metamorphic

Uses

Enargite is a significant ore of copper. 

Noteworthy Localities

Peru has produced some of the largest Enargite crystals, in a wide range of different localities. These include the Quiruvilca Mine, La Libertad Department; the Julcani Mine, Huancavelica Department; Casapalca, Lima Department; and the Morococha District, Junín Department. Other important worldwide localities include the Jinguashi Mine, Ruifang District, New Taipei City, Taiwan; and the Furtei Mine, Medio Campidano, Sardinia, Italy.

In the U.S., the premier locality for Enargite is the Butte District, Silver Bow Co., Montana, especially at the Leonard Mine and the East Colusa Mine. Good crystals have also from the Bingham Canyon Mine, Salt Lake Co., Utah; and from the Longfellow Mine, Red Mountain District, San Juan Co., Colorado.

Common Mineral Associations

Pyrite, Quartz, Chalcopyrite, Galena, Sphalerite, Barite, Covellite

Distingushing Similar Minerals

Manganite - Greater hardness, has reddish streak.
Tetrahedrite and Tennantite - Form in different crystal habits.


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