The Rock Cycle-Minerals form rocksAll rocks can be transformed into other rock typesRocks 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

(Heat & Pressure)Eruption or near surface cooling & crystallizationErosion

Magma molten rock below Earth'ssurface.Lava magma on the Earth's surface.Pyroclastic material (pyro = fire, clastic = debris) Airborne lava cools as it falls 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 throughTemperature of the melt Not only how hot, but how long it stays that hot also relates to pressure of the molten rockCooling environment fast vs slow Internal vs ExternalWater content

Bowen's Reaction Series-Important !OlivinePlagioclase(Na-feldspar)BiotiteQuartzPyroxeneAmphiboleMuscovitePlagioclase(Ca-feldspar)Orthoclase(K-feldspar)DiscontinuousContinuous

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

Composition of Igneous rocksFelsic 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

Viscosity of Magma/ LavaViscosity 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 FelsicRelated to: amount of water (H2O) in magma amount of silica (Si) in magma Mafic thin, low viscosity Felsic thick, high viscosity

Aphanitic basalt (mafic composition) constitutes the groundmassPorphyritic textureLarge white crystals are phenocryts

Intrusive rocks cool beneath Earth's surface cool very slowly higher P & T Phaneritic texturesExtrusive rocks cool on the Earth's Surface cool relatively fast lower T & P Aphanitic textures Pyroclastic texturesComplex Porphyritic texturesCategories of Igneous EOF Partially cools below and aboveGraniteBasalt porphyryRhyolite

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.PegmatiteFeldspar mineral grainQuartz mineral grainBiotite mineralgrain

What are the textures in these two rocks ?

What are the textures in these two rocks ?

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

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

VolcanicGlassObsidian- conchoidal fracture And association with volcanic rocks

Tuffs & BrecciasTuffs & Breccias- look like sedimentary rockBut they are not.it is volcanic ash that is lithified

Tuffs - may be welded or notAlways consists of fragments smaller than 2mm in diameterWelded means they were still hot enough that they partially recrystallized they were emplaced and consolidated.If they are not welded, it means they were not hot enough to partially recrystallize when they settled on the landscapeBreccias - have a tuffaceous matrix but have a large percentage of coarse-grained angular fragment. They may be welded or not too.

How do we tell where the igneous rocks formed? What can we derive from the rocks about the conditions of formation?

BatholithVolcanic neckIgneous dikeIgneous SillLava flowPyroclastics

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 rockIt cuts across other rocksAn igneous sill-Concordant with surrounding rockIt runs parallel to other rocks

NeckDikeigneous sillIgneous sillVolcanic Necks & Igneous Dikes

Lava flows

Flood basalts create lava cliffs on the Columbia Plateau