Types of Rocks Fonte: Google images Collecting and classifying rocks can be a rewarding pastime. Both rocks and minerals play an important part of our lives through the many products made from them. Rocks provide most of our material needs, much of our power, and most of our national and state wealth. The study of rocks is called petrology and forms part of the science of geology. Rocks are classified according to their origin. The main classes of rocks are: Igneous rocks: which crystallise or solidify from a molten state. Sedimentary rocks: made up or fragments of pre-existing rock, biogenic material or chemical precipitates. Metamorphic rocks: formed from the alteration of pre-existing rocks due to heat and pressure in the earth. Igneous Rocks Igneous rocks all form by the cooling of molten material known as magma. This can occur at or near the surface, at shallow depths in the earth’s crust, or deep in the crust. Igneous rocks which f...
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