Notes Igneous Rock

Think About… How can two rocks made of the same minerals look very different?

Magma vs Lava Deep inside Earth, temperatures are hot enough (750 to 1250 degrees C) to melt rock.

Magma vs Lava Molten rock inside Earth is called magma. Molten rock that reaches the surface is called lava.

Magma and Lava Rock formed from magma can have the same minerals as a rock formed from lava, but they will have different crystal structures and different names.

Intrusive vs Extrusive Igneous rocks are classified based on its minerals and the size of its crystals (also called: grain size or texture)

Intrusive vs Extrusive Intrusive igneous rock forms when magma cools inside Earth. Example: Granite (made of Quartz, Feldspar, and Mica)

Intrusive vs Extrusive Extrusive igneous rock forms when lava cools on Earth’s surface. Example: Rhyolite (made of Quartz, Feldspar, and Mica)

Intrusive vs Extrusive Granite and rhyolite have the same minerals (Quartz, Feldspar, Mica) but were formed in different ways.

Texture Texture (of an igneous rock)- the size of its mineral crystals (also called grain size).

Texture Large crystals form in intrusive igneous rock because:

Texture Inside Earth is very hot High temperatures make the magma cool slowly Slow cooling allows time for large crystals to form

Texture Very small crystals form in extrusive rocks because…

Texture The surface of Earth is cooler. Lower temperatures cause lava to cool quickly. There is no time for large crystals to form.

Identifying Igneous Rock To identify igneous rocks, you can look at texture and mineral composition.

Identifying Igneous Rock Most igneous rocks are made up of silicate minerals.

Identifying Igneous Rock Silicate minerals contain silica, a mixture of silicon and oxygen.

Identifying Igneous Rock Geologists sometimes classify igneous rocks based on how much silica they have.

Identifying Igneous Rock You can estimate how much silica is in an igneous rock by looking at its color.

Identifying Igneous Rock Igneous rocks with a lot of silica are light in color. Examples: granite and rhyolite

Identifying Igneous Rock Igneous rocks with little silica are dark in color. Examples: Gabbro and basalt

Landforms A landform is a natural feature on Earth’s land surface.

Landforms Ship Rock in New Mexico is an example of a landform made of igneous rock.

Landforms As hot magma pushes toward Earth’s surface, it makes formations underground.

Landforms When the rock above the formation wears away, we have intrusive rock on the surface.

Landforms When magma reaches Earth’s surface before cooling, the lava can erupt in different ways.

Landforms Lava that has very little silica flows easily and spreads out in thin sheets.

Landforms Lava that has a lot of silica does not flow easily, and usually results in violent eruptions.

Review Geologists classify an igneous rock on the basis of its crystal size and the amount of ______ its minerals contain. Carbon Silica Sediment Foliation

Review 2. What kind of texture would obsidian (an igneous rock) have if it cooled very quickly while it was being formed? Multicolored and banded Smooth and shiny with no visible grains Coarse grains Made up of jagged grains

Review 3. What is the classification of a rock formed inside Earth with large, visible grains? Intrusive igneous Sedimentary Metamorphic Extrusive igneous