Bornite
Bornite is a popular mineral for collecting but rarely available as a gem that is faceted. It is typically found as massive, opaque, metallic material with a copper-red color on fresh exposures which quickly tarnish to an iridescent purple after exposure to atmosphere and dampness. Bornite may be confused with tarnished Chalcopyrite.
Bornite is an copper that is important mineral along with other copper ores such as Chalcopyrite, Covellite, Cuprite, Digenite and Tetrahedrite. Good crystals are rare and so Bornite is commonly known simply as a mineral ore that is massive. It really is popular among children in souvenir shops where it’s offered as “peacock ore” or “peacock copper” due to its colorful tarnish that is iridescent. The colors are from an iridescent tarnish that forms on Bornite upon experience of air. The tarnish is constructed of assorted copper oxides or hydroxides that form a really layer that is thin the Bornite. In the event of Bornite, the tarnish may have a purplish, violet or color that is blue. The peacock ore could have many colors ranging from purple to blue to green to yellowish because bornite is often intergrown with Chalcopyrite which tarnishes to more greens and yellows.
Essential localities for fine crystals include: in the united states, from Butte, Silver Bow County, Montana, and at Bristol, Hartford County, Connecticut. In England, from the Carn Brea mine, Illogan, and elsewhere in Cornwall. Large crystals from the Mangula mine, Lomagundi district, Zimbabwe. From the Frossnitz Alpe, eastern Tirol, Austria. At Dzhezkazgan, Kazakhstan. In the N’ouva mine, Talate, Morocco.
| Chemical Formula: | Cu5FeS4 |
| Copper Iron Sulfide | |
| Molecular Weight: | 501.84 gm |
| Composition: | Iron | 11.13 % | Fe | ||
| Copper | 63.31 % | Cu | |||
| Sulfur | 25.56 % | S | |||
| 100.00 % |
| Crystallography: | Orthorhombic – Dipyramidal |
| Crystal Habit: | Crystals pseudocubic, dodecahedral, octahedral, to 6 cm; commonly granular, compact, or massive, disseminated. |
| Twinning: | On {111}; commonly shows penetration twins |
| Cleavage: | Poor/Indistinct; in traces on [111] |
| Fracture: | Irregular/Uneven, Conchoidal, Subconshoidal |
| Tenacity: | Brittle |
| Moh’s Hardness: | 3.0 – 3.25 |
| Density: | 5.06 – 5.09 (g/cm3) |
| Luminescence: | None |
| Radioactivity: | Not Radioactive |
| Other: | Magnetic after heating |
| Color: | Copper Red, Bronze Brown; tarnishing to an iridescent purplish surface after exposure to air and moisture |
| Transparency: | Opaque |
| Luster: | Metallic |
| Refractive Index: | R: (400) 19.9, (420) 18.8, (440) 17.9, (460) 17.6, (480) 18.0, (500) 18.8, (520) 20.0, (540) 21.3, (560) 22.9, (580) 24.4, (600) 26.0, (620) 27.5, (640) 28.8, (660) 30.2, (680) 31.6, (700) 32.7 |
| Birefringence: | None (opaque) |
| Dispersion: | None |
| Pleochroism: | Weak but noticeable |
| Anisotrophism: | Weak; Color in reflected light: Brown, Pinkish |
