*** Welcome to piglix ***

Bornite

Bornite
Bornite-Quartz-135210.jpg
Lightly iridescent bornite crystal on quartz needles from Kazakhstan (size: 3.6 x 2.2 x 1.2 cm)
General
Category Sulfide mineral
Formula
(repeating unit)
Cu5FeS4
Strunz classification 2.BA.10
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pbca
Unit cell a = 10.95 Å, b = 21.862 Å,
c = 10.95 Å; Z = 16
Identification
Formula mass 501.88 g/mol
Color Copper red, bronze brown, purple
Crystal habit Granular, massive, disseminated - Crystals pseudocubic, dodecahedral, octahedral
Twinning Penetration twins on [111]
Cleavage Poor on [111].
Fracture Uneven to subconchoidal; brittle
Tenacity Brittle
Mohs scale hardness 3 - 3.25
Luster Metallic if fresh, iridescent tarnish
Streak grayish black
Specific gravity 5.06 - 5.08
Refractive index Opaque
Pleochroism Weak but noticeable
Other characteristics Magnetic after heating, iridescent
References

Bornite, also known as peacock ore, is a sulfide mineral with chemical composition Cu5FeS4 that crystallizes in the orthorhombic system (pseudo-cubic).

Bornite has a brown to copper-red color on fresh surfaces that tarnishes to various iridescent shades of blue to purple in places. Its striking iridescence gives it the nickname peacock copper or peacock ore.

Bornite is an important copper ore mineral and occurs widely in porphyry copper deposits along with the more common chalcopyrite. Chalcopyrite and bornite are both typically replaced by chalcocite and covellite in the supergene enrichment zone of copper deposits. Bornite is also found as disseminations in mafic igneous rocks, in contact metamorphic skarn deposits, in pegmatites and in sedimentary cupriferous shales. It is important as an ore for its copper content of about 63 percent by mass.

At temperatures above 228 °C (442 °F), the structure is isometric with a unit cell that is about 5.50 Å on an edge. This structure is based on cubic close-packed sulfur atoms, with copper and iron atoms randomly distributed into six of the eight tetrahedral sites located in the octants of the cube. With cooling, the Fe and Cu become ordered, so that 5.5 Å subcells in which all eight tetrahedral sites are filled alternate with subcells in which only four of the tetrahedral sites are filled; symmetry is reduced to orthorhombic.


...
Wikipedia

...