Coltan Ore

Tantalum is a heavy, hard gray metal. Pure tantalum is ductile and may be drawn into very fine wire. Tantalum is practically immune to chemical attack at temperatures lower than 150 °C. It is only attacked by hydrofluoric acid, acidic solutions of the fluoride ion, and free sulfur trioxide. Alkalis attack tantalum very slowly. At higher temperatures, tantalum is more reactive. The melting point of tantalum is very high, exceeded only by that of tungsten and rhenium. The melting point of tantalum is 2996 °C; boiling point is 5425 +- 100 °C; specific gravity is 16.654; valence is usually 5, but may be 2, 3, or 4.