IGNEOUS ROCKS Introduction Igneous Compositions Igneous Textures Classification

PSCI 131: Igneous Rocks – Introduction Rocks • Most are aggregates of mineral crystals

PSCI 131: Igneous Rocks – Introduction Rocks • Igneous • Sedimentary • Metamorphic

PSCI 131: Igneous Rocks – Introduction Igneous Rocks • Form by cooling and crystallization

PSCI 131: Igneous Rocks – Introduction Igneous Rocks • What kind of igneous rock

PSCI 131: Igneous Rocks – Compositions Igneous Rock Compositions • What minerals the rock

PSCI 131: Igneous Rocks – Compositions Igneous Rock Compositions • Percentage of dark silicate

PSCI 131: Igneous Rocks – Compositions GRANITIC • 0 -25% dark minerals From: geology.

PSCI 131: Igneous Rocks – Compositions GRANITIC • 0 -25% dark minerals From: itc.

PSCI 131: Igneous Rocks – Compositions ANDESITIC • 25 -45% dark minerals DIORITE: This

PSCI 131: Igneous Rocks – Compositions BASALTIC • 45 -85% dark minerals This GABBRO

PSCI 131: Igneous Rocks – Textures IGNEOUS TEXTURES • Visual appearance, not feel •

PSCI 131: Igneous Rocks – Textures Coarse-grained • Most crystals visible to naked eye

PSCI 131: Igneous Rocks – Textures Coarse-grained • Slow cooling rate deep within crust

PSCI 131: Igneous Rocks – Textures Fine-grained • Most crystals not visible to naked

PSCI 131: Igneous Rocks – Textures Fine-grained • Rapid cooling rate on surface (volcanism)

PSCI 131: Igneous Rocks – Textures PORPHYRITIC • Two distinct crystal sizes in same

PSCI 131: Igneous Rocks – Textures PORPHYRITIC • Two-stage cooling – First, slow cooling

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • GLASSY – Very fast cooling

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • VESICULAR – Vesicles (bubbles) –

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • PYROCLASTIC – Ash and rock

PSCI 131: Igneous Rocks – Classification CLASSIFICATION • Based on texture and composition •

PSCI 131: Igneous Rocks – Classification CLASSIFICATION TABLE GRANITIC ANDESITIC BASALTIC COARSE-GRAINED Granite Diorite

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IGNEOUS ROCKS • • Introduction Igneous Compositions Igneous Textures Classification

Igneous Rocks Introduction

PSCI 131: Igneous Rocks – Introduction Rocks • Most are aggregates of mineral crystals • A few kinds of rocks aren’t made of minerals Granite is made of mineral crystals Images from: geology. com Obsidian (volcanic glass) has no mineral crystals

PSCI 131: Igneous Rocks – Introduction Rocks • Igneous • Sedimentary • Metamorphic

PSCI 131: Igneous Rocks – Introduction Igneous Rocks • Form by cooling and crystallization of magma From: en. wikipedia. org From: meteorites. wustl. edu

PSCI 131: Igneous Rocks – Introduction Igneous Rocks • What kind of igneous rock will form when a magma crystallizes? • Depends on: –Magma’s chemical composition –Magma’s cooling rate

Igneous Rocks Igneous Compositions

PSCI 131: Igneous Rocks – Compositions Igneous Rock Compositions • What minerals the rock is made of Orthoclase Quartz Hornblende From: geology. com

PSCI 131: Igneous Rocks – Compositions Igneous Rock Compositions • Percentage of dark silicate minerals From: geology. com From: ux 1. eiu. edu From: nwnature. net

PSCI 131: Igneous Rocks – Compositions GRANITIC • 0 -25% dark minerals From: geology. com This GRANITE contains about 10% dark minerals

PSCI 131: Igneous Rocks – Compositions GRANITIC • 0 -25% dark minerals From: itc. gsw. edu RHYOLITE is also felsic in composition

PSCI 131: Igneous Rocks – Compositions ANDESITIC • 25 -45% dark minerals DIORITE: This sample is about 40% dark crystals From: nwnature. net ANDESITE: Another intermediate rock From: geology. com

PSCI 131: Igneous Rocks – Compositions BASALTIC • 45 -85% dark minerals This GABBRO contains about 70% dark minerals From: ux 1. eiu. edu BASALT: Light silicate crystals are present, but are too small to see without magnification From: geology. com

Igneous Rocks Igneous Textures

PSCI 131: Igneous Rocks – Textures IGNEOUS TEXTURES • Visual appearance, not feel • Usually refers to size of mineral crystals • Determined by magma’s rate of cooling

PSCI 131: Igneous Rocks – Textures Coarse-grained • Most crystals visible to naked eye From: geology. com From: nwnature. net

PSCI 131: Igneous Rocks – Textures Coarse-grained • Slow cooling rate deep within crust • Crystals have time to accumulate more atoms & grow large From: windows 2 universe. org

PSCI 131: Igneous Rocks – Textures Fine-grained • Most crystals not visible to naked eye From: geology. com From: itc. gsw. edu

PSCI 131: Igneous Rocks – Textures Fine-grained • Rapid cooling rate on surface (volcanism) • Not enough time for crystals to grow large From: bbc. co. uk

PSCI 131: Igneous Rocks – Textures PORPHYRITIC • Two distinct crystal sizes in same rock Phenocrysts Groundmass From: geo 1. tcu. edu

PSCI 131: Igneous Rocks – Textures PORPHYRITIC • Two distinct crystal sizes in same rock Phenocrysts Groundmass From: pitt. edu

PSCI 131: Igneous Rocks – Textures PORPHYRITIC • Two-stage cooling – First, slow cooling produces phenocrysts – Then, rapid cooling of remaining magma produces groundmass

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • GLASSY – Very fast cooling – No time for any crystals to form

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • VESICULAR – Vesicles (bubbles) – Gas trapped in rapidly cooling magma From: texasbeyondhistory. net

PSCI 131: Igneous Rocks – Textures OTHER TEXTURES • PYROCLASTIC – Ash and rock fragments – Violent volcanic eruptions Ash matrix Rock fragments

Igneous Rocks CLASSIFICATION

PSCI 131: Igneous Rocks – Classification CLASSIFICATION • Based on texture and composition • Some rocks can be classified based only on texture

PSCI 131: Igneous Rocks – Classification CLASSIFICATION TABLE GRANITIC ANDESITIC BASALTIC COARSE-GRAINED Granite Diorite Gabbro FINE-GRAINED Rhyolite Andesite Basalt GLASSY OBSIDIAN VESICULAR SCORIA (dark) PUMICE (light) PYROCLASTIC WELDED TUFF PORPHYRITIC: Used as a modifier for any of the six basic rock names.

End of Igneous Rocks