Igneous Rocks Mt. Rushmore

Half Dome, Yosemite, CA Ansel Adams

IGNEOUS ROCKS Some igneous rocks form from cooled lava that has exited Earth’s crust Hawaii

Half Dome, Yosemite, California Some Igneous rocks cool from magma inside Earth and later become exposed through pressure, uplift, and erosion!!! Half Dome, Yosemite, California

Igneous Think of “ignite” To light a fire Igneous rock comes from the heat within Earth: Geothermal

How are Igneous Rocks Classified? Igneous rocks are classified by: 1. Mineral Composition 2. Crystal Size (Texture)

Igneous Rock Formation Most Igneous rocks form directly from Magma which is hot, molten rock Granite is the most common igneous rock, it cooled from magma Igneous rocks can also form from lava

3. First Classification of Magma: Felsic Is rich in Silica (SiO2) Small amounts of Ca, Fe, Mg (Calcium, Iron, & Magnesium) Slow-moving, thick= HIGH VISCOSITY (resistance to flowing) Crystallizes to light-colored minerals Resulting rocks have relatively low density Felsic rocks make up the continents

Examples of FELSIC igneous rocks Pumice Rhyolite

4. Second Classification of Magma: Mafic Low amounts of Silica (SiO2) Fe and Mg rich (Iron and Magnesium) Fast-moving, thinner= LOW Viscosity: less resistance to flowing, more fluid Crystallize to dark-colored minerals Resulting rocks have relatively high density Mafic rocks make up the ocean floors

Mafic Igneous Rock examples: Basalt (ocean floor) Gabbro

5. Crystal Size It takes time to grow crystals As magma cools, it crystallizes If magma cools slowly, what size crystals will form? Large Crystals If Magma cools quickly, small crystals will form because they have little time to grow.

Igneous Rock Obsidian cools so fast that no crystals have time to form A.K.A. Volcanic glass Obsidian is dark in color due to iron oxides.

6. Igneous Rocks Granite Intrusive Igneous rock that crystallizes below Earth’s surface, from magma Intrusive= Inside Earth Large Crystal size Notice how Granite has large crystals, it cooled slowly from magma deep beneath Earth’s surface

Igneous Rocks Extrusive Igneous rock that crystallizes or forms at Earth’s surface, from lava Extrusive= exited Earth Basalt Small Crystal size Notice how basalt has small crystals, it cooled quickly at Earth’s surface

Lava is magma that has reached the Earth’s surface.

Igneous Rocks EXT-rusive EXITED Earth Formed IN-side Earth IN-trusive Formed IN-side Earth

Crystal Size Extrusive Rock (Small crystal size) Intrusive Rock (Large Crystal Size) Because it is inside the Earth, it cools very slowly, giving crystals time to grow Extrusive Rock (Small crystal size) Cools very quickly so crystals do not have time to form

Composition (what it’s made of) of Granite Granite Rock contains the following minerals: Quartz Feldspar Mica

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

Igneous Rock Felsic Mafic Intrusive Extrusive (Light Color) Continents Mafic (Dark Color) Ocean Floor Intrusive Cools slowly From Magma Large crystals (SiO2) rich Fe, Mg rich Extrusive Cools quickly From Lava Small or no crystals

IGNEOUS FELSIC Light colored Less dense Rich in silica (SiO2) Magma flows slowly, thick Continental crust

IGNEOUS MAFIC Dark colored Very dense Rich in iron (Fe) and magnesium (Mg) Magma flows quickly, thin Oceanic crust

IGNEOUS EXTRUSIVE “exit” Magma exits the Earth before cooling Cools and crystalizes quickly Small or no crystals

IGNEOUS INTRUSIVE “in” Magma cools inside the Earth Cools and crystalizes slowly Large crystals

Igneous Rock Lab Use your Igneous observations sheet Rotate independently between the 25 stations set up around the room Start with whichever station number you are located Round 1: You will have less than 1 minute at each station Do not switch to the next station until told to do so, only 1 person at at station (if you have extra time, study your notes) Round 2: You may go back to any unoccupied station, if needed