Bornite

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UNDER CONSTRUCTION


Can you help make this a better article? What good localities have we missed? Can you supply pictures of better specimens than those we show here? Can you give us more and better information about the specimens from these localities? Can you supply better geological or historical information on these localities?

Bornite Display Collections

Cu₅FeS₄ cubic and tetragonal

Though a common Cu ore, xls are quite rare. An old English name for Bornite is Horse Flesh Ore. Apparently the rose brown colour of fresh bornite resembles horse flesh. It really is amazing to watch fresh bornite tarnish quickly within a minute or so. Other old names are Peacock Ore and Erubescite alluding to the remarkable purple shades of the tarnished ore. The tarnish is a thin layer of Iron hydroxides over a layer of Blue Remaining Covellite¹. The interference colours (like gasoline on water) probably come from the layer of hydroxides.

Tarnished Bornite with Chalcopyrite 6 cm	© Carlos Medina

Bornite can be confused with tarnished Chalcopyrite, Covellite, and the much more rare Digenite. None of these are rose brown on fresh fracture. Attacking blue tarnished Chalcopyrite with a needle reveals the golden yellow Chalcopyrite underneath. Chalcopyrite and Bornite have a similar structure so one can expect an epitaxi between the two.

The structure of Bornite is based on a cubic close packing of sulfur atoms with metals in the tetrahedral sites. At temperatures higher than 228 C it crystallizes in the cubic system. At lower temperatures the metals can be disordered and there are several varieties. The lowest temperature variety is tetragonal. All crystallized Bornites with distinct xls show isometric forms.

Since the 1700's Cornwall in England has produced the most crystallized specimens which are still highly regarded and now dispersed world wide. Cornwall today produces little if any of the calbre of the old timers.The crystals on Cornish specimens frequently exceed 1 cm in size. Rarely, they were as large as 1.5 cm. The best specimens came from the mines along the foot of Carn Brea and Carn Entral, between Camborne and Redruth: Carn Brea, Tincroft, Dolcoath, and Cook's Kitchen. On old labels, locality is often just given as "Redruth", and in mostt cases, attribution to a specific mine is impossible. Good ones also came from the "United Mines" at Gwennap (another generic name, which may refer either to the St Day United Mines or to the Gwennap United Mines, both in Gwennap parish, but independent on each other), and from Botallack. (Peter Haas 2010)

Cornwall Bornite 17 cm	©

Exceptional bornites, some might say the finest, to over 2 cm were recovered here from an alpine cleft (!) in the 19th century.[www.mindat.org]

The Butte mines produced sharp crystals to a couple of cm. Messina in South Africa produced bigger crystals, but they are not quite so sharp. They get at least 5cm in size and probably get bigger than that. (David Von Bargen 2010)

The Mangula Mine in Zimbabwe I believe produced the world's finest bornite crystals. The ore was mainly massive bornite in coarse limestones. The crystals occurred as isolated, floater, very sharp, rhombic dodecahedrons with faintly striated faces and a submetallic lustre in coarsely crystaline white to buff white calcite and reached up to 7-8cm diameter. The largest I ever saw was in the Messina Mines office at Messina in 1974. It was the size of an orange. This crystal together with an 8 x 2 cm chalcocite xtl from Messina, which were both in the mine office display case, vanished when the Messina Mine shut down. I bought my crystal which is about 5cm diameter with some matrix attached from a chemist in Nairobi in 1976 who had worked in Mangula. The specimen is on display in the Branner Library at Stanford University. Apparently the University of Witwatersrand collection also had some single crystals. (Demetrius Pohl 2010)

Mangula Bornite Intergrown Trapezohedra 7cm	©

Recently some of the best ones have come from Dzhezkazgan. There were clean sharp dodecs and trapezohedrons to several cm.

1) Vaughan D J, Tossell J A, Stanley C J (1987) The surface properties of bornite, Mineralogical Magazine, 51, 285-293

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Edited 23 time(s). Last edit at 12/13/2010 10:30PM by Rob Woodside.

Another old name is "erubescite", alluding to the purple shades of the tarnished ore. In modern times, the best ones certainly came from Dzhezkazgan. There is, however, at least one historic locality which produced outstanding specimens:

[www.mindat.org]

Exceptional bornites to over 2 cm were recovered here from an alpine cleft (!) in the 19th century. Since this appears to have been a very limited find, it is unlikely that we will get a photo. Perhaps, the museum at Vienna still keeps specimens and Uwe might be able to at least tell us about them ?

The crystals on Cornish specimens frequently exceed 1 cm in size. Rarely, they were as large as 1.5 cm. The best specimens came from the mines along the foot of Carn Brea and Carn Entral, between Camborne and Redruth: Carn Brea, Tincroft, Dolcoath, and Cook's Kitchen. On old labels, locality is often just given as "Redruth", and in mostt cases, attribution to a specific mine is impossible. Good ones also came from the "United Mines" at Gwennap (another generic name, which may refer either to the St Day United Mines or to the Gwennap United Mines, both in Gwennap parish, but independent on each other), and from Botallack.

The Butte mines produced sharp crystals to a couple of cm. Messina in South Africa produced bigger crystals, but they are not quite so sharp. They get at least 5cm in size and probably get bigger than that.

Thanks Peter and David.
I went to Vienna in 1987, learned the meaning of Geschlossen Dienstag, and spent an extra day in expensive Vienna in hopes of seeing that Bornite. When I got into the museum on Wednesday there were wonderful treasures that made the lost day very well worth it. However that Bornite was on loan to some provincial museum and I missed it. Min Rec has a photo of it and Maybe Uwe does too. It would make a needed addition to the article. How many of the Bornites were found I only know of the Vienna one?

English bornite single xls to 1.5 cm?!! live and learn!!!.

I'll add you material and try to flesh it out and find some pictures. I'm mathering about a paragraph on the xl structure. I recall something about high and low temp forms but must look this up.

The Mangula Mine in Zimbabwe I believe produced the world's finest bornite crystals. The ore was mainly massive bornite in coarse limestones. The crystals occurred as isolated, floater, very sharp, rhombic dodecahedrons with faintly striated faces and a submetallic lustre in coarsely crystaline white to buff white calcite and reached up to 7-8cm diameter. The largest I ever saw was in the Messina Mines office at Messina in 1974. It was the size of an orange. This crystal together with an 8 x 2 cm chalcocite xtl from Messina, which were both in the mine office display case, vanished when the Messina Mine shut down. I bought my crystal which is about 5cm diameter with some matrix attached from a chemist in Nairobi in 1976 who had worked in Mangula. The specimen is on display in the Branner Library at Stanford University. Apparently the University of Witwatersrand collection also had some single crystals.

Thank you very much Demetrius. Are their any photos?

Rob,
About the large Alpine Bornites (up to 5kg crystals, with gold on them!); They were found at the Virschnitzscharte in East-Tirol by the strahler Jestl from Virgen. After his great find he became crazy and destroyed the best specimens. So, it's probably uncertain how many were found.

Thanks Harjo. I've got to get back to this and will insert what you said. Any photos of that material?

Hi Rob and all.

Kipushi in R.D.C. produced in the late 50's some excellent bornites.
Unfortunately they where quite rare but I managed to get one.
Here it is : [www.mindat.org]

I have a good specimen from Tsumeb too and will take a pic and post it here.

I hope this helps.

Take care and best regards.

Paul.

Thanks Paul. I will certainly use that. In Fact I think it is in the long list of photos I've culled from the gallery and should go through for a proper write up.

I'd love to see the Tsumeb piece.

Hey Rob,

Remember the double crystal from Mangula I had at the Pacific Mineral Museum? I'll have to see if I have a photo of it somehwere. I think someone had also posted a photo of it online after I showed it at the 2003 Tucson show.

Mark

Hi Mark. See you in Seattle at Bart's Show later this month?

It would be great if you could find that photo.Theonly Mangula Bornite photo we have is Rock's:




Do you know anything more about the locality?, Number of Specimens produced?, etc?

Rob,

Both Park City and Tintic produced bornite crystals to 1cm. I think I have a couple of Park City Specimens that I can photograph and add. I have seen some nice tintic ones over the years but I don't think I own one.

Rick
I know I am in my own little world, but everyone knows me here.

Thanks Rick. I must get back to this. A photo would be great.