Igneous Rocks

From the latin word “ignis” (which means “fire”), igneous rocks are those that form from the cooling and crystallization of magma From the latin word “ignis” (which means “fire”), igneous rocks are those that form from the cooling and crystallization of magma

Composition Igneous Rocks are made up of minerals, and … Igneous Rocks are made up of minerals, and … Minerals are made up of crystals, and … Minerals are made up of crystals, and … Crystals are made up of atoms. Crystals are made up of atoms.

Texture Extrusive Igneous Rock: Fine-grained (small crystals), igneous rock that cools quickly ON Earth’s surface (think EXTERIOR) Extrusive Igneous Rock: Fine-grained (small crystals), igneous rock that cools quickly ON Earth’s surface (think EXTERIOR)

Texture Intrusive Igneous Rocks: Coarse-grained (large crystals) igneous rock that cools slowly beneath Earth’s surface (think INTERIOR). Intrusive Igneous Rocks: Coarse-grained (large crystals) igneous rock that cools slowly beneath Earth’s surface (think INTERIOR).

Ultimately, the texture is determined by the rate of cooling

Magma vs. Lava Magma is… molten material found beneath Earth’s surface. Magma is… molten material found beneath Earth’s surface. Lava is… molten material that flows out on to Earth’s surface Lava is… molten material that flows out on to Earth’s surface Regardless of whether it is considered magma or lava, it contains the following elements… Regardless of whether it is considered magma or lava, it contains the following elements… oxygen oxygen silicon silicon aluminum aluminum iron iron magnesium magnesium calcium calcium sodium sodium Both magma and lava can cool to form igneous rocks Both magma and lava can cool to form igneous rocks

Three factors involved in the formation of magma… * temperature * temperature * water content * water content * pressure * pressure

Three Types of Magma Rhyolitic Rhyolitic High Silica Content (about 70%) High Silica Content (about 70%) Creates Explosive Volcanoes Creates Explosive Volcanoes Thick and Chunky (like oatmeal) Thick and Chunky (like oatmeal)

Three Types of Magma Andesitic Andesitic Medium Silica Content (about 60%) Medium Silica Content (about 60%) A mixture of rhyolitic magma and basaltic magma A mixture of rhyolitic magma and basaltic magma Volcanoes can be mildly explosive Volcanoes can be mildly explosive

Three Types of Magma Basaltic Basaltic Low silica content (50% or less) Low silica content (50% or less) Thin and runny (think hot maple syrup) Thin and runny (think hot maple syrup) Volcanoes are not explosive and lava flows smoothly Volcanoes are not explosive and lava flows smoothly The Hawaiian Islands are Shield Volcanoes, that spill basaltic magma The Hawaiian Islands are Shield Volcanoes, that spill basaltic magma

Where this magma comes from

Bowen’s Reaction Series An illustration that demonstrates how minerals form in a predictable pattern as magma cools. An illustration that demonstrates how minerals form in a predictable pattern as magma cools.

Classifying Igneous Rocks Felsic Igneous Rocks: Igneous rocks (such as granite) that are light in color, have a high silica (SiO2) content, and contain minerals such as quarts, orthoclase feldspar, plagioclase feldspar. Felsic Igneous Rocks: Igneous rocks (such as granite) that are light in color, have a high silica (SiO2) content, and contain minerals such as quarts, orthoclase feldspar, plagioclase feldspar.

Classification Cont… Mafic Igneous Rocks: Igneous rocks (such as gabbro) that are dark in color, have a lower silica (SiO2) content, are rich in iron (Fe) and Magnesium (Mg) Mafic Igneous Rocks: Igneous rocks (such as gabbro) that are dark in color, have a lower silica (SiO2) content, are rich in iron (Fe) and Magnesium (Mg)

Classification Cont… Intermediate Igneous Rocks: A little bit of both. Intermediate Igneous Rocks: A little bit of both. Ultra-Mafic Igneous Rocks: Igenous rocks that have a VERY low silica content, and a VERY high iron and magnesium content Ultra-Mafic Igneous Rocks: Igenous rocks that have a VERY low silica content, and a VERY high iron and magnesium content

A Few Exceptions… Porphyritic: An igneous rock that has both fine-grained crystals AND coarse-grained crystals. Porphyritic: An igneous rock that has both fine-grained crystals AND coarse-grained crystals.

Another Exception Pegmatites: A vein of extremely large crystals found in an otherwise fine- grained igneous rock. Pegmatites: A vein of extremely large crystals found in an otherwise fine- grained igneous rock.

And one more… Kimberlites: A rare, ultra-mafic igneous rock that contains diamonds. Kimberlites: A rare, ultra-mafic igneous rock that contains diamonds.

Igneous Rocks in N. America Plutonic Volcanic Plutonic Volcanic