Chapter 5 “Igneous Rock”

Objectives Describe how the cooling rate of magma & lava affects the texture of igneous rocks. Classify igneous rocks according to their mineral composition. Describe a number of identifiable rock structures.

2 types of Igneous Rocks Intrusive Extrusive Created inside the earth Created on top of the ground

Intrusive Igneous Rocks Magma cools slowly underground Creates large, well-developed crystals Example: Granite

Extrusive Igneous Rocks                                                                     Extrusive Igneous Rocks Created when lava cools rapidly Examples: Basalt (oceans) Obsidian (glass) Pumice (has gas bubbles)

What happens if the outside cools rapidly – but the inside cools slowly? Creates a rock with a porphyritic texture. Small crystals outside Quickly formed Larger crystals embedded inside Formed slowly

Mineral Composition of Igneous Rocks #1 Felsic High in silica (SiO) Examples: Feldspar, quartz, mica Granite, Rhyolite, Obsidian #2  Intermediate #3  Mafic

Mineral Composition of Igneous Rocks (cont.) #2  Intermediate Medium colored (grays/browns/reds) Pink Feldspar Diorite, Andesite

Mineral Composition of Igneous Rocks (cont.) #3  Mafic Rich in Magnesium & Iron Heavy & dense Olivine, Hornblende Basalt, Gabbro

Igneous Rock Structures 3rd start here wed Igneous Rock Structures Intrusions Formed inside the earth Extrusions Formed on the surface

Igneous Intrusions Batholiths Means “deep rock” Large igneous formations Must be over 100 km2 The continents are underlain by large batholiths Similar, smaller areas are called “stocks”

Intrusions (cont.) Laccolith Means “layer of rock” Found in groups Bubbles of magma that have cooled underground Usually mushroom shaped

Intrusions (cont.) Sill Dikes A flat layer of solidified magma Vertical columns of solidified magma

Igneous Extrusions Volcanic Neck What’s left of an ancient volcano May also include exposed fingers of hardened lava known as dikes

Igneous Extrusions (cont.) Lava flows Flat layers of solidified lava

Igneous Extrusions (cont.) Lava plateau Wide, flat areas of hardened lava

Assignments: Complete Chapter 4 interactive notes for Homework

Intrusive VS Extrusive Groups Felsic Intermediate Mafic Intrusive VS Extrusive