Warm Up 10/2 On Front White Board On Front White Board

Igneous Rocks Chapter 3, Section 2

Formation of Igneous Rocks Rocks that form when magma hardens beneath Earth’s surface are called intrusive igneous rocks Rocks that form when magma hardens beneath Earth’s surface are called intrusive igneous rocks They have intruded into the existing rocks They have intruded into the existing rocks As magma rises it cools, allowing elements to combine and form minerals, which combine to form igneous rocks As magma rises it cools, allowing elements to combine and form minerals, which combine to form igneous rocks When lava hardens, the rocks that form are called extrusive igneous rocks When lava hardens, the rocks that form are called extrusive igneous rocks The have extruded onto the surface The have extruded onto the surface

Evolution of a Magma

Formation of Igneous Rocks Intrusive - Granite Extrusive - Rhyolite

Classification of Igneous Rocks Texture and composition are two characteristics used to classify igneous rocks Texture and composition are two characteristics used to classify igneous rocks Texture describes the appearance of an igneous rock based on its size, shape, and arrangement of interlocking crystals Texture describes the appearance of an igneous rock based on its size, shape, and arrangement of interlocking crystals Composition describes the proportions of light and dark minerals in the rock Composition describes the proportions of light and dark minerals in the rock

Course/Fine-Grained Texture If the magma cools slowly, it will have only have a few centers of crystal growth If the magma cools slowly, it will have only have a few centers of crystal growth Slow cooling results in the formation of large crystals (course-grained) Slow cooling results in the formation of large crystals (course-grained) If magma or lava cools rapidly, a large number of tiny crystals compete for available ions If magma or lava cools rapidly, a large number of tiny crystals compete for available ions Rapid cooling of magma or lava results in rocks with small, interconnected mineral grains (fine-grained) Rapid cooling of magma or lava results in rocks with small, interconnected mineral grains (fine-grained)

Course/Fine-Grained Texture Course-Grained GabbroFine-Grained Basalt

Glassy/Porphyritic Texture Glassy Texture – solids produced so quickly that the ions are not able to align Glassy Texture – solids produced so quickly that the ions are not able to align Porphyritic Texture – rocks that have different size minerals, a result of different rates of cooling Porphyritic Texture – rocks that have different size minerals, a result of different rates of cooling

Glassy/Porphyritic Texture Glassy Texture - ObsidianPorphyritic Texture - Andesite

Concept Check How does the rate of cooling of magma or lava affect the texture of igneous rocks? How does the rate of cooling of magma or lava affect the texture of igneous rocks? A slowly cooling magma or lava will produce rocks in which the mineral grains are relatively large. Quickly cooling molten material will result in rocks with small mineral grains. Lava that cools rapidly will produce a glassy rock. Rocks that form as a result of different cooling rates will have both large and small mineral grains. A slowly cooling magma or lava will produce rocks in which the mineral grains are relatively large. Quickly cooling molten material will result in rocks with small mineral grains. Lava that cools rapidly will produce a glassy rock. Rocks that form as a result of different cooling rates will have both large and small mineral grains.

Granitic/Basaltic Composition Granitic Composition – Igneous rocks in which quartz and feldspar are the dominant minerals Granitic Composition – Igneous rocks in which quartz and feldspar are the dominant minerals Most granitic rocks also contain about 10% dark silicate minerals and 70% light silicate minerals Most granitic rocks also contain about 10% dark silicate minerals and 70% light silicate minerals Basaltic Composition – rocks that contain many dark silicate minerals Basaltic Composition – rocks that contain many dark silicate minerals Basaltic rocks are rich in iron and magnesium Basaltic rocks are rich in iron and magnesium

Granitic/Basaltic Composition Granitic Composition - GraniteBasaltic Composition - Gabbro

Other Compositional Groups Andesitic Composition – rocks with a composition between granitic and basaltic Andesitic Composition – rocks with a composition between granitic and basaltic Andesitic rocks contain at least 25% dark silicate minerals Andesitic rocks contain at least 25% dark silicate minerals Ultramafic – rocks that are composed mostly of dark silicate minerals Ultramafic – rocks that are composed mostly of dark silicate minerals Peridotite is an example of an ultramafic rock, although rare on the crust, it is thought that the mantle is made mostly of peridotite Peridotite is an example of an ultramafic rock, although rare on the crust, it is thought that the mantle is made mostly of peridotite

Other Compositional Groups Andesitic Composition - AndesiteUltramafic - Peridotite

Bowen’s Reaction Series

Classification of Igneous Rocks

Concept Check Describe the main differences between granitic and basaltic rocks? Describe the main differences between granitic and basaltic rocks? Granitic rocks contain mostly quartz and feldspar and thus are light-colored. Basaltic rocks are rich in iron and thus are dark-colored and more dense. Granitic rocks contain mostly quartz and feldspar and thus are light-colored. Basaltic rocks are rich in iron and thus are dark-colored and more dense.

Homework Read Chapter 3, Section 2 (pg ) Read Chapter 3, Section 2 (pg ) Do 3.2 Assessment #1-7 (pg. 74) Do 3.2 Assessment #1-7 (pg. 74) Print out “Investigation 3 – Classifying Rocks Using a Key” for next class Print out “Investigation 3 – Classifying Rocks Using a Key” for next class

Assignment Create a Rock Cycle Poster! Create a Rock Cycle Poster! Your poster should have: Your poster should have: a. Captions (5 points) b. Color (5 points) c. Drawings of each step (5 points) d. Be neat (5 points) You may use page 67 of the text to guide you. You may use page 67 of the text to guide you.