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Rock Types. Igneous, Sedimentary, and Metamorphic. Igneous Rocks. Igneous Rocks. Word comes from the Latin Ignis , meaning fire Formed from the solidification or cooling of magma Can form below the surface or above the surface
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Rock Types Igneous, Sedimentary, and Metamorphic
Igneous Rocks • Word comes from the Latin Ignis, meaning fire • Formed from the solidification or cooling of magma • Can form below the surface or above the surface • Over 700 types of igneous rocks having been described, most forming beneath the surface
Intrusive Igneous Rocks • Also called plutonic rocks • Form from magma that cools within the crust (under the surface) • Magma cools slowly under the surface, so rocks are coarse grained and mineral crystals can be easily seen • Often make up the central core of mountain ranges and can be seen after erosion • Granite is the most common intrusive rock, other examples include diorite, gabbro, and pegmatite
Pegmatite • http://geology.com/rocks/pictures/granite-large-orthoclase-250.jpghttp://geology.com/rocks/pictures/granite-large-orthoclase-250.jpg Gabbro Diorite Granite
Extrusive Igneous Rocks • Also called volcanic rocks • Form at the Earth’s surface as lava from the mantle and lower crust cools • Cools quickly, so rocks are fine grained and you can’t see individual mineral crystals • Often takes lab work to identify these rocks as mineral composition is hard to determine • Examples include Andesite, Basalt, Pumice, Obsidian, Rhyolite, and Scoria
Basalt Andesite Rhyolite Pumice Scoria Obsidian
Chemical Classification • Igneous rocks can also be classified by their compositions • The amount of silica (SiO2 ) in the rock determines it classification
Felsic Igneous Rocks • Have a silica content of greater than 63% • Usually have a light color because of this • Examples include Granite and Rhyolite
Intermediate Igneous Rocks • Have a silica content between 52% and 63% • Tend to appear grey • Examples include Andesite and Diorite
Mafic Igneous Rocks • Have low silica (between 45% and 52%) and high iron-magnesium content • Tend to be black in color • Include Basalt and Gabbro
Ultramafic Igneous Rocks • Igneous rocks with less than 45% silica • Tend to be very dark, and may have a greenish tint • The mantle is made up of ultramafic rock • Include picrite, komatite,peridotite
Where Igneous Rocks are Found • The deep sea floor- Most of the ocean floor is made of basalt • Under continents- If you drill deep enough under any continent you will eventually hit granite • Volcanic island arcs and the edge of continents where there are volcanoes( crust collides forming subduction zones) • Any areas around volcanoes
Sedimentary Rocks • Form at the Earth’s surface, usually under water • Consist of layers called strata (sometimes called stratified rocks) • Sediment that forms these rocks comes from weathering and erosion before being deposited by wind, water, or the mass movement of glaciers • Layers of sedimentary rock give us useful information about the Earth’s history
Clastic Sedimentary Rocks • The most common type of sedimentary rocks • Rocks that form from sediments: mud, sand, gravel, and clay • These sediments, or clasts, get cemented over time with low heat and pressure forming rocks • Include sandstone (sand), shale (clay), conglomerate (gravel and pebbles), Breccia (re-cemented bits of broken rock)
Sandstone Conglomerate Shale Breccia
Organic Sedimentary Rocks • Rocks which form from the remains of living organisms • Form in the sea, primarily from the shells of plankton which pile up as organisms die • Limestone and chert form from this process • Plant material can also pile up, forming bituminous coal
Chert Limestone Bituminous Coal
Chemical Sedimentary Rocks • Forms when minerals come out of a solution (also called precipitating) • Often occur when shallow seas begin drying up • Calcite comes out of the liquid first, then gypsum, then halite • Forms some varieties of limestone and dolomite, as well as rock gypsum and rock salt
Chemical Limestone Rock Salt Rock Gypsum
Where Sedimentary Rocks are Found • Cover the surface of all continents, but make up only 8% of the crust’s volume • Often associated with rivers, lake beds, peat bogs, and deserts.
Metamorphic Rocks • Name means “shape changed” • Form when rocks are changed or metamorphosed deep underground • Four main factors contribute to metamorphism • Heat • Pressure • Strain • Fluids
Metamorphic Rock Terms • Protolith- Original rock before it is metamorphosed • Index Minerals- Minerals like garnet that are associated with metamorphism • Foliation- The layering within metamorphic rocks, usually take spiral like patterns. Some metamorphic rocks are foliated, while others are nonfoliated • Facies- Different categories of metamorphic rocks based on their mineral and chemical composition
Types of metamorphism • Contact Metamorphism • Metamorphism that occurs when magma heats nearby rock • Regional Metamorphism • Metamorphism that usually occurs over large areas of continental crust, usually associated with mountain ranges because of plates moving
Foliated Metamorphic Rocks Slate Gneiss Schist
Nonfoliated Metamorphic Rocks Quartzite Marble Amphibolite
Where Metamorphic Rocks are Found • Deep underground • At the bases of mountains • Areas lining plutons, pegmatites, or other magma chambers • Often exposed at the surface after major erosion • Make up about 85% of the Earth’s continental crust (continental crust is much thicker than oceanic crust)
