Rocks are made up of minerals, usually several, but sometimes only one or two. Minerals are either uncombined elements or compounds (made up of different elements).

What is a Mineral?

Almost all minerals are solid (except water, mercury, and opal). They have a definite atomic structure and chemical composition. For example, if you had two quartz crystals, they would have similar chemical and physical properties. To identify a mineral,you can observe its color, luster, hardness, specific gravity, and streak. Fracture and cleavage may be obvious, or you may have to break the mineral.

What is a Rock?

Rocks are classified into three major groups- igneous, metamorphic, and sedimentary. Rocks are aggregates of different minerals, which are fused, cemented, or bound together. Rocks can be identified using the same methods as minerals.