page_title: Cobalt
section_title: Characteristics
hierarchical_section_title: Cobalt / Characteristics
caption_attribution_description: Deutsch: Kobalt, Stück aus einer Elektrolytplatte, Reinheit 99,9&#160;% English: Cobalt, Piece of an electrolytically made plate, 99.9&#160;% pure
context_page_description: Cobalt is a chemical element with the symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.
  Cobalt-based blue pigments have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought to be due to the known metal bismuth. Miners had long used the name kobold ore for some of the blue-pigment-producing minerals; they were so named because they were poor in known metals, and gave poisonous arsenic-containing fumes when smelted. In 1735, such ores were found to be reducible to a new metal, and this was ultimately named for the kobold.
  Today, some cobalt is produced specifically from one of a number of metallic-lustered ores, such as cobaltite. The element is, however, more usually produced as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo and Zambia yields most of the global cobalt production.
context_section_description: Cobalt is a ferromagnetic metal with a specific gravity of 8.9. The Curie temperature is 1,115 °C (2,039 °F) and the magnetic moment is 1.6–1.7 Bohr magnetons per atom. Cobalt has a relative permeability two-thirds that of iron. Metallic cobalt occurs as two crystallographic structures: hcp and fcc. The ideal transition temperature between the hcp and fcc structures is 450 °C (842 °F), but in practice the energy difference between them is so small that random intergrowth of the two is common.
  Cobalt is a weakly reducing metal that is protected from oxidation by a passivating oxide film. It is attacked by halogens and sulfur. Heating in oxygen produces Co₃O₄ which loses oxygen at 900 °C (1,650 °F) to give the monoxide CoO. The metal reacts with fluorine (F₂) at 520 K to give CoF₃; with chlorine (Cl₂), bromine (Br₂) and iodine (I₂), producing equivalent binary halides. It does not react with hydrogen gas (H₂) or nitrogen gas (N₂) even when heated, but it does react with boron, carbon, phosphorus, arsenic and sulfur. At ordinary temperatures, it reacts slowly with mineral acids, and very slowly with moist, but not with dry, air.
caption: A block of electrolytically refined cobalt (99.9% purity) cut from a large plate
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