Minerals are naturally occurring inorganic solids that make up rocks. There are four properties used to identify minerals: color, luster, streak, and hardness. Streak is the color of the mineral's powder and can differ from its solid color. Hardness refers to a mineral's resistance to scratching - if a mineral can be scratched by another substance, it is less hard than that substance. The document also defines the three main types of rocks - igneous, sedimentary, and metamorphic - and how each forms.
