How Do Rocks Form Anyway?

Igneous Rocks (Rocks from Fire)

 Rocks formed from the cooling of hot, molten rock (magma or lava)

 Two Types o Intrusive . Cooling of magma deep beneath the surface . Magma contained in batholiths (large), dikes (angled), sills (horizontal) . Magma intrudes (advances by burning its way into existing rock) . Cool very slowly - form large crystals . Examples: Granite, Gabbro, Diorite

o Extrusive . Cooling of magma (near surface) or lava (at surface) . Cool quickly - form small crystals . Examples: Basalt, Rhyolite, Andesite, Obsidian, Pumice, Scoria

Sedimentary Rocks (Rocks from the Surface)

 Rocks formed from the lithification (compaction and cementation) of sediment

 Sediment o Broken up pieces of rock and/or organic materials o Mostly sand, silt, and clay o Made from weathering and erosion of rocks

 Compaction o As sediments are deposited and buried by layer upon layer o Force from above pushes sediment together

 Cementation o Water carries dissolved minerals thru sediment o Compaction forces water and air out and minerals are left behind as the cement

 Three Types o Clastic . Rock fragments (any combo of size and shape) are compacted and cemented together (ex. conglomerate, breccia, sandstone) . Can be formed from pressure only (ex. shale)

o Chemical . Minerals that were once dissolved in water . Evaporation - water leaves minerals behind (ex. rock salt is left behind by water) . Precipitation - minerals fall out of water due to temperature change in the water (ex. chert, compact limestone)

 Organic o Remains of once living things . Ex. Coal from plants . Ex. Fossiliferous limestone, coquina, and chalk from the shells of tiny marine animals Metamorphic Rocks (Rocks from Heat and Pressure)

 Metamorphosis - changing of one rock into another by heat, pressure, and/or chemical processes

 Minerals in rock change in size & shape and may form parallel bands or layers

 Two types o Contact . Metamorphism due to rock coming into direct contact with magma o Regional . Heat and pressure due to tectonic activity . Most met. rocks are formed by regional metamorphism