Igneous rocks are formed by the cooling and hardening of molten material called magma . The word igneous comes from the Latin word igneus, meaning fire. There are two types of igneous rocks: intrusive and extrusive. Exam- elation: Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet. When lava comes out of a volcano and solidifies into extrusive igneous rock, also called volcanic, the rock cools very quickly. Rocks are formed on Earth as igneous, sedimentary, or metamorphic rocks. Igneous rocks form when rocks are heated to the melting point which forms magma . ... This changing of rock types is called the "Rock Cycle". Solid rock can be changed into a new rock by stresses that cause an increase in heat and pressure. A rock is a naturally formed, non-living Earth material. Rocks are made of minerals. The minerals may be so tiny that you can only see them with a microscope.
Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified: magma that cools slowly will form an igneous rock with large crystals. lava that cools quickly will form an igneous rock with small crystals. their visual appearance shows individual crystals interlocked together to form the rock mass. The cooling of magma deep in the Earth is typically much slower than the cooling process at the surface, so larger crystals can grow. Intrusive igneous rocks form in magma chambers that are deep underground. Many kilometers below the Earth's surface, molten rock called magma flows into cracks or underground chambers. There, the magma sits, cooling very slowly over thousands to millions of years. An intrusion is a body of igneous (created under intense heat) rock that has crystallized from molten magma. Gravity influences the placement of igneous rocks because it acts on the density differences between the magma and the surrounding wall rocks (country or local rocks). The most common river rocks used in landscaping and decorative construction are made of granite. Granite belongs to the "intrusive" category of igneous rock, which means it formed below the earth's surface as magma slowly cooled and crystallized. The rocks that form Earth's crust are continually destroyed and remade in an endless process called the rock cycle. Rock is formed by melting; by cooling and solidifying; by changing through heat and pressure; by weathering and erosion; and by compression and cementation.
