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Cogwheel Shaped Bournonite

The Mineral bournonite

Bournonite has the distinction of being known as "cogwheel ore", due to the unique twinning habit where crystals form in a rough cruciform form with pitted, deeply striated edges. The early German miners called this mineral "radelerz" or wheel ore, describing the cogwheel habit. Bournonite can be very lustrous, with a bright metallic luster, though it sometimes develops a dulling tarnish.

Bournonite was positively identified in 1804 by French mineralogist and crystallographer Count Jacques Louis de Bournon (1751–1825), founder of the Geological Society of London. The name given by Bournon for this mineral was Endellione (later Endellionite), after the Cornish locality where it was first described, but subsequently the name was changed to Bournonite in Bournon's honor.
Chemical Formula PbCuSbS3
Composition Lead and copper antimony sulfide, often with some arsenic
Variable Formula PbCu(Sb,As)S3
Color Steel gray to black. May also be iridescent with a colorful metallic film.
Streak Dark gray to nearly black
Hardness 2.5 - 3
Crystal System Orthorhombic
3D Crystal Atlas
(Click for animated model) 
Crystal Forms
and Aggregates
In short and distinct prismatic or tabular crystals, usually deeply striated. Also in groups of parallel or penetrating crystals. Often in repeated twins that form a very unique "cogwheel" or cross-shaped formations. Also columnar, as rectangular blades, grainy, and massive.
Transparency Opaque
Specific Gravity 5.8 - 5.9
Luster Metallic
Cleavage 2,1;3,2
Fracture Subconchoidal to uneven
Tenacity Brittle
In Group Sulfides; Sulfosalts
Striking Features Distinct crystal and twinning habits.
In mesothermal vein deposits.
Rock Type Sedimentary, Metamorphic
Popularity (1-4) 2
Prevalence (1-3) 3
Demand (1-3) 1

Bournonite AUCTIONS
Cog Wheel Ore

Bournonite is a minor ore of copper and lead. It is a highly desirable mineral among collectors, with well-formed crystals, especially the twinned "cogwheels", highly valued among collectors. Good examples from classic European localities such as Cornwall command exceptionally high prices for collectors.

A classic locality that once produced outstanding Bournonite crystals is the Herodsfoot Mine, Lanreath, Liskeard District, Cornwall, England. The old type locality for Bournonite is also in Cornwall at Wheal Boys, Port Isaac. Excellent crystal clusters of thick crystals have come from France at the Les Malines District, Saint-Laurent-le-Minier, Gard. Fine Bournonite has also come from the Georg Mine, Willroth, Altenkirchen, Rhineland-Palatinate, Germany; and from Příbram, Bohemia, Czech Republic. Several of the Transylvanian ore mines in Maramureș Co., Romania have produced good forms of this mineral, especially Baia Sprie and Cavnic (Kapnik), where the Bournonite occurs in dense crystal clusters.

A relatively recent find of exceptionally large and lustrous Bournonite crystals is the Yaogangxian Mine, Yizhang, Hunan Province, China. This locality has set a new standard for this species, with some of the largest and most lustrous crystals ever found. Nice crystal groups have come from the Chichibu Mine, Nakatsugawa, Saitama Prefecture, Japan.

Excellent Bournonite crystals, often tabular with a squared shape, are well known from the Machacamarca District, Potosí Department, Bolivia. Several of the silver ore deposits in Peru have produced fine crystal clusters, especially the Quiruvilca Mine, La Libertad Department; the Pachapaqui District, Ancash Department; the Casapalca Mine, Lima Department; and Cerro de Pasco, Pasco Department. In Mexico, good Bournonite crystals have come from the Noche Buena Mine, Mazapil, Zacatecas; Conception del Oro, Zacatecas; and Naica, Chihuahua. Good Bournonite is very rare in the U.S, where its most prominent locality is the Silver King Mine, Park City, Summit Co., Utah.

Quartz, Pyrite, Tetrahedrite, Siderite, Dolomite, Sphalerite, Chalcopyrite, Galena, Barite

Enargite - Slightly lower specific gravity, doesn't form in unique twins; otherwise difficult to distinguish.

bournonite PHOTOS
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