In this class we are going to learn about the definition Rocks and igneous type of rocks and their classification
Rocks -A consolidated material composed of grains of one or more minerals. Classification of Rocks 1. Igneous Rocks -Rocks formed when molten material from the earth’s interior cools and solidifies on or beneath the earth’s surface. Types of Igneous Rocks a) Intrusive Igneous Rocks-Rocks formed when magma cools and solidifies below the earth’s surface e.g. granite, diorite, gabbro, peridotite. -Have coarse texture as a result of slow cooling giving minerals more time to form large crystals. - Are classified further into two: (i) Hypabyssal rocks - intrusive igneous rocks which are near the earth’s surface. (ii) Plutonic rocks- Intrusive igneous rocks which are deep below the surface. b) Extrusive Igneous Rocks - Rocks formed when lava solidifies on the earth’s surface. - Have fine texture due to fast cooling giving minerals less time to collect together to form larger crystals. -They are of two types namely:(i) Volcanic Ejecta - Extrusive igneous rocks formed in the following ways: • When ash and lava ejected from underground as they fall on the earth’s surface e.g. pumice. • When dust and ash ejected settle on the ground and get compressed to form a rock e.g. tuff. (ii) Lava Flows-Extrusive igneous rocks formed when basic lava flows over a considerable distance then cools and solidifies e.g. basalt and obsidian.