(the best!) Igneous Rocks

Igneous textures: Magma Lava Pyroclastics Molten rock solidifies below surface Coarse grained Lava Molten rock solidifies at/near surface Fine grained Pyroclastics Chunks/pieces of molten rock blown into air Clasts welded together

Chemistry Composition: what minerals make up the rock Affected by: Tectonics Melt source Country rock Temperature Water content

Bowen’s Reaction Series

Composition (Mode) 3 general categories of igneous rock: Mafic Rich in Ca, Mg, Fe Si poor (45-52%) High T, low H2O content Less viscous Intermediate Felsic Si (>69%), K, Al rich Lower T, high H2O More viscous

Texture Phaneritic Aphanitic Porphyritic Crystals are large enough to see Aphanitic Microscopic crystals Porphyritic Two different crystal sizes (due to change in temp as cooling) Phenocrysts Matrix

Porphyritic texture Large white crystals are phenocryts Aphanitic basalt (mafic composition) constitutes the groundmass

Granite and Rhyolite: Felsic What are the textures in these two rocks ? Phaneritic Aphanitic

Andesite & Diorite: Intermediate Aphanitic Phaneritic What are the textures in these two rocks ?

Basalt & Gabbro: Mafic Aphanitic Phaneritic

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

Volcanic Glass Obsidian- conchoidal fracture And association with volcanic rocks Volcanic Glass

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

Pyroclastics Lava flow Volcanic neck Igneous dike Igneous Sill Batholith

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

Sierra Nevada Batholith

Intrusions Igneous rock pushes between or through pre-existing rock Dike Rock cuts through Sill Rock is parallel to pre-existing Neck Cooled core of extrusion Laccolith Makes bulge shape between rock layers

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

Volcanic Necks & Igneous Dikes igneous sill Igneous sill