Sulfur. Vaguely hellish and certainly associated with all things hot and stinky, this powdery element can sometimes be bought in drug stores and is often typo'd as "sulphur". On rare occasion it is found in nature as a translucent yellow crystal but more often as powder stain near volcanoes. It is an essential ingredient in the making of rubber and is infamous for that awful smell of rotten eggs - which is actually the deadly gas hydrogen sulfide!
You have two choices. The lab created and translucent crystals or the economical opaque type.