Rocks

Rocks Naturally occurring solid mixtures of one or more minerals and organic matter They can be made of two or more different minerals that have been: cemented together squeezed and heated together melted and cooled together

Types of Rocks Igneous Sedimentary Metamorphic

Igneous rocks are classified in three ways: Most igneous rocks are produced deep underground by the cooling and hardening of magma. Igneous rocks are classified in three ways: Origin – where they are formed Composition – refers to the minerals that make up the rock Texture – the shape, size, arrangement and distribution of minerals that make up the rock

Origin Intrusive - Formed deep within the earth Granite Extrusive- Formed from lava; volcanic Pumice Obsidian

Intrusive Igneous Rocks Intrusive igneous rocks are formed deep within the Earth Granite is the most common (continental crust) Quartz Mica Hornblende Feldspar Intrusive masses named for their size and shape

Plutons are large irregularly shaped intrusions Batholiths – largest intrusive bodies Stocks – smaller areas than batholiths Sills – sheet-like intrusions parallel to previous layers Dikes - sheet-like intrusions that cut across previous rock layers at an angle

Intrusive Igneous Rocks Pegmatite Granite Diorite Gabbro

Extrusive Igneous Rocks Formed from lava; volcanic Basalt is the most common (oceanic crust) Cools quickly and contains very small, or no crystals Can erupt from fissures, which are long cracks in the Earth

Extrusive Igneous Rocks Obsidian Pumice Rhyolite Andesite Basalt Scoria

Composition Refers to the minerals that make up the rock Felsic light-colored rocks less dense contain elements such as aluminum, potassium, silicon, & sodium Mafic dark-colored rocks denser rich in calcium, iron and magnesium (poor in silicon)

The size of the crystals depends on: Texture – refers to the shape, size, arrangement and distribution of the minerals that make up the rock Fine-grained Coarse-grained Glassy Porphyritic The size of the crystals depends on: Rapid cooling = fine-grained with small crystals Slow cooling = coarse-grained with large crystals

Textures Glassy Coarse-grained Granite Obsidian Fine-grained Porphyritic Basalt Granite

Composition and Texture of Igneous Rock