Antimony was recognized in compounds by the ancients and was known as a metal at the beginning of the 17th century and possibly much earlier. It is not abundant, but is found in over 100 mineral species. The yellow form, obtained by oxidation of stibine, SbH3, is probably impure, and is not a distinct form. Natural antimony is made of two stable isotopes, 121Sb and 123Sb. Forty four other radioactive isotopes and isomers are now recognized.
Metallic antimony is an extremely brittle metal of a flaky, crystalline texture.
It is bluish white and has a metallic luster. It is not acted on by air at room temperature, but burns brilliantly when heated with the formation of white fumes of Sb2O3. It is a poor conductor of heat and electricity, and has a hardness of 3 to 3.5. Commercial-grade antimony is widely used in alloys with percentages ranging from 1 to 20. It greatly increases the hardness and mechanical strength of lead.