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 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

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

Composition of the magma Analogous to what makes up the “stew" What chemical elements are present What material has the magma moved through 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! Olivine Plagioclase (Na-feldspar) Biotite Quartz Pyroxene Amphibole Muscovite Plagioclase (Ca-feldspar) Orthoclase (K-feldspar) Discontinuous Continuous

Composition of Igneous rocks Felsic Intermediate Between the two extemes in Si content and color Mafic Si - poor (< 35%) rich in Ca, Fe, and Mg. light color Rich in Si, K, and Al Light color Very little Ca, Fe, and Mg

Viscosity of Magma/ Lava the resistance of a liquid to flow — — Viscosity- important for volcanic activity the resistance of a liquid to flow — high viscosity = thick and stiff — low viscosity = thin and "runny". Related to: Mafic — Felsic — 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- how big are the minerals? Igneous Rock Textures- how big are the minerals? Phaneritic Texture 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

Igneous Rock Textures: Phaneritic texture Mineral grains are visible Intrusive Aphanitic texture Grains too small to see Extrusive Porphyritic texture Larger grains in small grained matrix Cools above and below

Aphanitic basalt (mafic composition) constitutes the groundmass Porphyritic texture

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

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

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

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

What are the textures in these two rocks ? Granite Rhyolite

Andesite & Diorite What are the textures in these two rocks ?

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 a green appearance

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

Tuffs & Breccias Tuffs, Pumice & Breccias- look like sedimentary rock 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 from the rocks about the conditions of formation?

Batholith Volcanic neck Igneous dike Igneous Sill Lava flow Pyroclastics

Enchanted Rock is called an “Exfoliation Dome” because of the layers of rock that are exfoliating from the surface

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

Sierra Nevada Batholith

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

Neck Dike igneous sill Igneous sill Necks & Ig Dikes