Intermediate Division – Bornite, Purple Copper Ore Composition
Bornite. Purple Copper Ore, etc.
Composition. Cu5FeS4 = sulfur 25.5, copper 63.3, iron 11.2. analyses of different specimens show quite a wide variation in the percentages of the elements present, copper ranging form 55 to 71 per cent. Analyses of the purest material, however, agree with the above formula.
Crystallization. Isometric. Crystals rare. Usually in rough cubes, sometimes in penetration twins. Dodecahedron and octahedron at times
Structure. Commonly massive.
Physical Properties. H. = 3. G. = 4.9-5.4. Metallic luster. Color brownish bronze on fresh fracture but quickly tarnishing on exposure to variegated purple and blue and finally to almost black. Streak grayish black.
Test. Easily fusible at 2.5. Gives odor of sulfur dioxide on charcoal or in O. T. yields a very little sulfur in C. T. Becomes magnetic in R. F. If, adfter roasting, it is moistened with hydrochloric acid an heated, it gives an azure-blue flame (copper). Easily soluble in nitric acid with separation of sulfur; solution neutralized with ammonia gives red-brown precipitate of ferric hydroxide and blue color to filtrate. Characterized chiefly by its purple tarnish.
Occurrence. An important and widely occurring ore of copper, but usually with other copper minerals and in subordinate amount. It has been found as a primary constituent in igneous rocks and in pegmatite veins. Bornite and chalcopyrite are the two common original copper minerals, from which other copper minerals have been derived through secondary action. It is also frequently, itself, a secondary mineral formed in the upper, enriched zone of copper veins through the action of desending copper-bearing solutions, upon chalcopyrite, chalcocite, enargite, malachite, azurite pyrite, etc. It frequently occurs in intimate mixture with chalcopyrite and. Found in the United Estates at Butte, Montana. It was found in unusual crystasl, associated with crystallized chalcocite at Bristol, Connecticut. Occurs at Acton, Quebec, Canada. Found in Cornwall; Monte Catini, Tuscany, and in various other European countries. An important ore in Chile, Peru, Bolivia and Mexico.
Name. bornite was named after the mineralogist von Born (1742-1791). Sometimes called horseflesh ore in reference to the color on the fresh fracture, or variegated copper ore or peacock ore because of its purple tarnish. Called for the latter reason erubescite by English mineralogists.
Use. An important ore of copper.
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