tantalum (tănˈtələm) [key] [from Tantalus], metallic chemical element; symbol Ta; at. no. 73; at. wt. 180.94788; m.p. 2,996°C; b.p. 5,400±100°C; sp. gr. 16.65 at 20°C; valence +2, +3, +4, or +5. Tantalum is a rare, hard, blue-gray metal with a body-centered cubic crystalline structure. Its chemical characteristics resemble those of niobium, the element above it in Group 5 of the periodic table. Pure tantalum is extremely ductile and can be drawn into a very thin wire. It is malleable and highly resistant to common acids and to corrosion at temperatures below about 150°C. Tantalum is obtained chiefly from the mineral tantalite, although it also occurs in euxenite, samarskite, and some other rare minerals. The major sources of tantalum ore are Australia, Brazil, and Canada. Tantalum is almost always found in association with niobium; separation of the two metals is difficult. Major uses of tantalum include electrolytic capacitors, chemical equipment, and parts for vacuum furnaces, aircraft, and missiles. Tantalum was used in the filaments of electric light bulbs and electronic tubes but has been largely replaced by tungsten for these uses. It is often alloyed with other metals; it imparts strength, ductility, corrosion resistance, and a high melting point. Because it is unaffected by body fluids and causes no adverse tissue reactions, it is used in dental and surgical instruments and prostheses. Useful tantalum compounds include the carbide TaC2, an abrasive that is almost as hard as diamond; and the oxide Ta2O5, used in making special highly refractive glass. Tantalum was discovered in 1802 by A. G. Ekeberg but for some time was confused with niobium.