Igneous rocks originated with the movement of tectonic plates and they are associated with sea floor spreading, mountain forming, and the evolution of continents. They are rocks formed by the cooling and the solidification of molten silicate minerals (magma) and include volcanic and plutonic rocks. Magma is molten rock material consisting of liquid, gas and early-formed crystals. It is mobile and capable of penetrating into or through rocks of the earth's crust. Much of it cools deep in the Earth's crust, but some of it works its way to the surface and is extruded as lava. These lava eruptions have allowed scientists to study the nature of magma, its composition, its physical characteristics and its origin. The two main types of magma are:

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1. ���basaltic magma - typically very hot ranging from 900 to 1200 degrees celcius, and is highly fluid.

2. ���silicic magma - this is cooler, ranging below 800 degrees celcius, and is highly viscous.

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Igneous rocks are classified on the basis of texture and composition. The texture of a rock refers to the size, shape, and arrangement of the constituent mineral grains, for example, the rocks texture could be glassy, porphyritic etc.

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The composition refers to the elements or minerals that make up the rock. Some main kinds of igneous rocks are basalt, gabbro, andesite, diorite, rhyolite, and granite.

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When magma reaches the Earth's surface and flows out over the landscape as lava, it forms extrusive rock bodies. Magma that solidifies below the surface forms intrusive rock bodies.

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