This is a hard one. The lightest minerals have structures with lots of holes in them -- a good example is the class of minerals called zeolites that are related in composition to sand and clay (i.e. they contain the elements silicon, aluminum, and oxygen). Zeolites are used in detergents, deodorants, and most commonly, as kitty litter. Because of the holes (which make them light) they are also very good at trapping smelly chemicals, and this is what gives them their uses.