Sulfur is a nonmetallic chemical element which appears in numerous forms and compounds. It is used extensively in many industries, as are ions of sulfur such as sulfides and sulfates. In addition to having industrial applications, sulfur is also an important part of all living organisms, and it is also used as a food source by some bacteria, such as those found around hydrothermal vents.
In pure form, sulfur has a number of allotropes. Allotropic elements are elements which can have a number of pure structures; carbon is a well known allotropic element, appearing in the form of both diamonds and coal. Most of the allotropes of sulfur are crystalline in structure, although one is more plastic in nature. The most well known allotrope of sulfur appears in a yellow, odorless crystalline form which is also rather brittle. Many people are surprised to learn that sulfur is odorless; the rotten egg scent associated with sulfur is actually hydrogen sulfide, a dangerous sulfur compound.
The extremely reactive element is used in a number of applications including the manufacture of gunpowder, insecticides, and prescription drugs. It is also part of the vulcanization process for rubber, and it is the base for well-utilized compounds like sulfuric acid. In nature, sulfur can be found in compounds like galena and cinnabar, and it may also appear in pure deposits, especially around volcanoes and mineral springs.
Sulfur itself is generally safe to handle, but many sulfur compounds are more risky. Some are extremely toxic, and you should always be careful to follow listed precautions of chemicals like sulfur dioxide.