Minerals A mineral is a naturally occurring, inorganic solid with a definite chemical composition and crystal arrangement. A rock is a hard material made of one ore more minerals. There are thousands of known minerals in the world, but fewer than 50 minerals make up most of the rock material in the world. Minerals can be identified by their physical properties.
All physical properties come from the internal arrangement of atoms.
A small amount of an impurity can cause a severe change in color. Luster - the way a mineral shines. The mineral is scratched against materials with a known hardness to see which gets scratched. Streak - this is the color of the powdered mineral. The mineral is scratched against an unglazed tile to see the streak.