To identify a rock, it is necessary to consider its luster, color, hardness, cleavage and density. The geographical location of the rock should also be used to help identify it.
Rocks are typically classified as igneous, sedimentary or metamorphic. Igneous rocks can be either igneous-volcanic or igneous-plutonic. It is necessary to examine the overall appearance and hardness of the rock to determine which group the rock belongs to. For example, igneous-volcanic rocks are typically less dense than other rocks as a result of the many air holes present in the rock. Sedimentary rocks often appear to have many particles, whereas igneous-plutonic rocks are a solid mass that is smooth in texture.
The hardness of the rock also provides information on its classification. Limestone, for example, is a soft rock that is easily scratched, while granite is a very hard rock that does not scratch or break easily. The luster of the rock is determined by its metallic components. For example, some igneous-volcanic rocks are more lustrous than sedimentary rocks.
A rock's cleavage refers to its irregularities in shape. For instance, feldspar may have crevices that are cubic in appearance. The color of the rock is typically considered after other features, as the color is not as effective in identifying types of rocks as other features, such as hardness. The abundance of particular types of rocks and minerals available in the geographical region helps determine the specific type of rock being identified.