Sulfur powder is a refined and processed form of sulfur, a naturally occurring element that is bright yellow in color and is often known for the strong odor it gives off when burned. Many people compare the smell to rotten eggs.
Powdered forms usually have a bit of this smell, but it isn't normally very intense. The powder is commonly used as a dietary supplement, usually to improve joint health and muscular function, and it is widely believed to have clarifying properties for the skin. It has a number of more industrial uses, too, particularly as an additive to fertilizers and insecticides, and some cultures believe it has mystical or magical properties, particularly when burned.