The Rock Cycle Minerals form rocks All rocks

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The Rock Cycle. Minerals form rocks All rocks can be transformed into other rock

The Rock Cycle. Minerals form rocks All rocks can be transformed into other rock types Rocks are divided into 3 categories Igneous- crystalline- forms as liquid cools Metamorphic- crystalline-forms as rocks are heated and squeezed Sedimentary- non-crystalline- smaller pieces or chemicals from other rocks

Igneous formed from Magma and Lava Magma • molten rock below Earth's surface. L

Igneous formed from Magma and Lava Magma • molten rock below Earth's surface. L ava • magma on the Earth's surface. Pyroclastic material • (pyro = fire, clastic = debris) • Airborne lava — cools as it falls

Composition of the magma • Analogous to what makes up the “stew" • What

Composition of the magma • Analogous to what makes up the “stew" • What chemical elements are present • What material has the magma moved through Temperature of the melt • Not only how hot, but how long it stays that hot • also relates to pressure of the molten rock Cooling environment • fast vs slow • Internal vs External Water content

Bowen's Reaction Series- IMPORTANT! Plagioclase (Ca-feldspar) Olivine s uou tin con Amphibole Con tinuo

Bowen's Reaction Series- IMPORTANT! Plagioclase (Ca-feldspar) Olivine s uou tin con Amphibole Con tinuo us Dis Pyroxene Biotite Plagioclase (Na-feldspar) Orthoclase (K-feldspar) Muscovite Quartz

What things might you describe when looking at an igneous rock?

What things might you describe when looking at an igneous rock?

Composition of Igneous rocks Felsic or Sialic magma • Si-rich (> 65%) • rich

Composition of Igneous rocks Felsic or Sialic magma • Si-rich (> 65%) • rich in K, and Al • little Ca, Fe, and Mg. Intermediate magma • between the two extremes in Si content and other atoms. Mafic magma • Si - poor (< 35%) • richer in Ca, Fe, and Mg.

Ways of Changing Magma Composition

Ways of Changing Magma Composition

Viscosity of Magma/ Lava Viscosity- important for volcanic activity • the resistance of a

Viscosity of Magma/ Lava Viscosity- important for volcanic activity • the resistance of a liquid to flow — high viscosity = thick and stiff — low viscosity = thin and "runny". Related to: • amount of water (H 2 O) in magma • amount of silica (Si) in magma • Mafic — thin, low viscosity • Felsic — thick, high viscosity

Igneous Rock Textures. Phaneritic Texture how big are the minerals? • Visible Mineral Grains

Igneous Rock Textures. Phaneritic Texture how big are the minerals? • Visible Mineral Grains distinguishable as different colored interlocking shapes Aphanitic Texture • Mineral grains too small to be seen — microscopic Porphyritic Texture • Two distinct sizes of mineral grains • Large and Small — Large = Phenocrysts — Small = Groundmass or Matrix • Groundmass — Grains may be either visible or not

Porphyritic texture Aphanitic basalt (mafic composition) constitutes the groundmass

Porphyritic texture Aphanitic basalt (mafic composition) constitutes the groundmass

Cooling Histories Minerals need time and space to grow • More time = Bigger

Cooling Histories Minerals need time and space to grow • More time = Bigger crystals — visible mineral grains P & T control cooling rates of magma • Temp — Earth is a good insulator » holds in heat » keeps out cool — Atmosphere is a relatively bad insulator » transfers heat easily • Earth has pressure — Weight of overlying rocks — Magma trying to push up (density) — water vapor (steam), wants to expand

Categories of Igneous EOF Granite Intrusive rocks • cool beneath Earth's surface • cool

Categories of Igneous EOF Granite Intrusive rocks • cool beneath Earth's surface • cool very slowly • higher P & T — Phaneritic textures Extrusive rocks Rhyolite • cool on the Earth's Surface • cool relatively fast • lower T & P — Aphanitic textures Basalt — Pyroclastic textures porphyry Complex • Partially cools below and above — Porphyritic textures

Igneous rock names • determined by texture — size and arrangement of mineral grains

Igneous rock names • determined by texture — size and arrangement of mineral grains • AND by mineral composition — minerals affect rock color and indicate temperature of creation

Pegmatite A Pegmatite is a very coarse-grained igneous rock. Crystals are >2 cm, often

Pegmatite A Pegmatite is a very coarse-grained igneous rock. Crystals are >2 cm, often larger. Most are granitic, although mafic pegmatites can form. Biotite mineral grain Feldspar mineral grain Quartz mineral grain

Granite & Rhyolite Phaneritic Texture Felsic magma Granite What are the textures in these

Granite & Rhyolite Phaneritic Texture Felsic magma Granite What are the textures in these two rocks ? Aphanitic Texture Felsic magma Rhyolite

Andesite & Diorite Aphanitic texture forms from intermediate composition magma Phaneritic texture -forms from

Andesite & Diorite Aphanitic texture forms from intermediate composition magma Phaneritic texture -forms from intermediate composition magma What are the textures in these two rocks ?

Basalt & Gabbro aphanitic texture forms from mafic magma phaneritic texture forms from mafic

Basalt & Gabbro aphanitic texture forms from mafic magma phaneritic texture forms from mafic magma Basalt Gabbro »

Peridotite- the abundance of Olivine crystals (more than 40%) makes the rock take on

Peridotite- the abundance of Olivine crystals (more than 40%) makes the rock take on a green appearance

Obsidian- a popular rock among paleopeople for tool making Volcanic Glass

Obsidian- a popular rock among paleopeople for tool making Volcanic Glass

Tuffs &Tuffs Breccias - look like sedimentary rock & Breccias But they are not….

Tuffs &Tuffs Breccias - look like sedimentary rock & Breccias But they are not…. it is volcanic ash that is lithified

How do we tell where the igneous rocks formed and what can we derive

How do we tell where the igneous rocks formed and what can we derive from the rocks about the conditions of

Pyroclastics Lava flow Volcanic neck Igneous dike Igneous Sill Batholith

Pyroclastics Lava flow Volcanic neck Igneous dike Igneous Sill Batholith

Sierra Nevada Batholith- Home to Yosemite National Park and a lot of Granites and

Sierra Nevada Batholith- Home to Yosemite National Park and a lot of Granites and Grano -diorites

Sierra Nevada Batholith

Sierra Nevada Batholith

Areal extent of the Idaho Batholith- a huge (15, 400 square miles) intrusive body

Areal extent of the Idaho Batholith- a huge (15, 400 square miles) intrusive body of primarily felsic composition (granites) igneous rocks

An igneous dike. Discordant with surrounding rock It cuts across other rocks

An igneous dike. Discordant with surrounding rock It cuts across other rocks

An igneous sill. Concordant with surrounding rock It runs parallel to other rocks

An igneous sill. Concordant with surrounding rock It runs parallel to other rocks

Necks & Ig Dikes Neck Dike igneous Igneous sill

Necks & Ig Dikes Neck Dike igneous Igneous sill