Rocks are aggregates of minerals: Some rocks consist almost entirely of one mineral(example:limestine consists mostly of calcite), but usually rocks consist of major and minor accessory minerals. Whereas the major minerals are essential to the identity of the rock, the accessory minerals do not effect the bulk composition and have no bearing on how the rock is classified.

There are three kinds of rocks: Igneous, Sedimentary, and Metamorphic. Each unique in formation, yet related and intertwined as they change into each other –recording the history of the earth. Below are their stories.

Igneous rocks take their name from the latin root Ignis, which means fire. These "fire-formed" rocks form as molten rock cools. Magmas that cool at depth, cool more slowly, tend to have large mineral crystals, and are called intrusive or plutonic rocks. These rocks, with large mineral crystals, are described as having a phaneritic texture. That is, having mineral grains that you can easily see with the naked eye. On the other hand, lavas, molten rock that have been exposed to the air, cool much more rapidly and form extrusive rocks that have tiny or microscopic crystals (aphanitic texture) or none at all and often are glassy or have gas pockets.

The composition of igneous rocks vary from felsic to mafic. Mafic rocks contain a lot of magnesium and iron. The rocks make up a denser oceanic crust and are usaully dark in color. Felsic rocks contain a lot of silica and aluminum. These rocks make up the lower density continental crust and are usually light in color.

Metamorphic rocks are formed by increased temperature and pressure of the parent rocks. These changes rearrange mineral grains, enlarge crystals, and transform the chemistry of the parent rock. Metamorphic rocks are classified by texture. Those that have layered or banded texture are foliated. Conversely, nonfoliated rocks lack banding and usually contain only one mineral (massive).