first being used as tools for hunting and defence, and as building materials to construct shelters and monuments. If there were no rocks, we wouldn’t have soil for food, no tools, no shelter, no roads and not much left. Rocks are composed of tiny fragments of one or more materials called minerals. The rocks as well as the minerals are essential to the prosperity and cultural splendour of human civilization. The branch of geology dealing with the study of rocks is called petrology.
Rocks are made of grains that fit together. Each grain in the
rock is formed of a mineral, which is a naturally formed chemical compound. A rock is defined as a naturally occurring solid aggregate of one or more minerals or mineral-like matter (mineraloids). Such aggregates constitute the basic units of solid Earth. Rocks can be classified broadly into three groups.
Geologists classify rocks according to the processes that resulted in their formation. Three basic groups of rocks they recognize are: igneous rocks (those crystallized or solidified from molten rock material called magma or lava), sedimentary rocks (those consisting of fragments derived from pre-existing rocks or of materials precipitated from solutions) and metamorphic rocks (those formed by the alteration of existing rocks).
