Tungsten

1.

A rare element of the chromium group found in certain minerals, as wolfram and scheelite, and isolated as a heavy steel-gray metal which is very hard and infusible. It has both acid and basic properties. When alloyed in small quantities with steel, it greatly increases its hardness. Symbol W (Wolframium). Atomic weight, 183.6. Specific gravity, 18.

2.

Scheelite, or calcium tungstate.