Types of Rocks

Types of Rocks There are three main types of rocks: Igneous - formed when molten rock cools. Sedimentary – formed by the “cementing together” of small grains of sediment. Metamorphic – rocks changed by the effect of heat and pressure.

Igneous Rocks These are rocks formed by the cooling of molten rock (magma.) magma volcano Magma cools and solidifies forming igneous rocks

**The faster the magma cools, the smaller the crystals will be** Igneous Rocks Intrusive Igneous Rocks Cool INSIDE the earth Have LARGE crystals Extrusive Igneous Rocks Cool OUTSIDE the earth Have SMALL crystals **The faster the magma cools, the smaller the crystals will be**

Igneous Rocks This piece of obsidian cooled so FAST on the SURFACE that it did not have time to form any crystals.

Igneous Rocks This piece of rhyolite also cooled on the SURFACE very FAST and has small crystals.

Igneous Rocks This piece of granite cooled slowly INSIDE the Earth and has LARGE crystals.

Sedimentary Rocks Sedimentary Rocks are rocks formed when particles of sediment build up and are “cemented together” by the effect of pressure and minerals. Getting older sea Fragments washed to the sea Sedimentary rocks Rocks are broken up by the action of weathering

Sedimentary Rocks Have grains, which are the bits of sediments Grains can be big or small Sometimes rub off on your hands

Sedimentary Rocks The only rocks with FOSSILS

Sedimentary Rocks Sometimes layers are visible

Metamorphic Rocks Metamorphic rocks are formed by the effect of heat and pressure on existing rocks. This can greatly affect the hardness, texture or layer patterns of the rocks. Magma Pressure from surface rocks metamorphic rock forming here heat

Metamorphic Rocks There is a change in foliation (how the minerals line up)

Metamorphic Rocks Banded light and dark colors

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