3.4 – Igneous and Metamorphic Rocks Essential Questions: How Do Geologists Classify Igneous Rocks? What Are Metamorphic Rocks?

How Do Geologists Classify Igneous Rocks? Igneous rocks are classified by their origin, texture, and mineral composition.

Origin Extrusive rock is igneous rock formed from lava that erupted onto Earth’s surface. Basalt

Origin Intrusive rocks are formed when the magma beneath Earth’s surface cools and hardens. Granite Why is this granite intrusion above Earth’s surface?

Texture Texture depends on the size and shape of the mineral crystals. Crystal size depends on cooling rates.

Mineral Composition The amount of silica determines an igneous rocks color.

Uses of Igneous Rocks Igneous rocks tend to be hard, dense, and durable. Building material Tools Landscaping

What Are Metamorphic Rocks? Deep inside Earth, pressure and temperature are high. Any rock that forms from another rock as a result of changes in heat and/or pressure is a metamorphic rock.

How Do Metamorphic Rocks Form? Metamorphic rocks can form from igneous, sedimentary, or other metamorphic rocks.

How Do Metamorphic Rocks Form? Magma inside the Earth can heat rocks to change them. High pressure deep inside the Earth can also change rocks. Minerals can become other minerals. Shapes can change.

How Metamorphic Rocks are Classified Geologists classify metamorphic rocks according to the arrangement of the grains which have changed due to intense heat and pressure.

How Metamorphic Rocks are Classified Rocks can become foliated, flattened and layered. This can change the minerals inside the rocks also. Granite  Gneiss Shale  Slate

How Metamorphic Rocks Are Used Marble (from Quartzite, a sedimentary rock made from the mineral quartz) is easy to sculpt and polish.

How Metamorphic Rocks Are Used Slate (a foliated version of the sedimentary rock shale) splits easily into flat pieces and comes in many colors which are good for roofing and old fashioned blackboards.