ROCK NOTES Big Idea: Igneous, metamorphic, and sedimentary rocks formed in different ways. Rocks of each type have unique characteristics that can be used to identify them. Rock: mixture of minerals, usually cemented together Rocks Igneous Intrusive Sedimentary Extrusive Metamorphic Foliated Nonfoliated IGNEOUS ROCK Big Idea: Igneous rocks form when hot magma cools and hardens. Molten rock: melted minerals Magma: molten rock inside Earth Lava: magma that reaches Earth’s surface Intrusive: igneous rock that forms slowly from magma cooling below the surface. Intrusive rocks are only at Earth’s surface if forces such as erosion, volcanoes, landslides, or earthquakes expose them. Examples: granite Extrusive: igneous rock that form as lava cools on Earth’s surface. Examples: rhyolite, basalt, obsidian, pumice, andesite SEDIMENTARY ROCK Big Idea: Sedimentary rocks form when sediments are pressed and cemented together or when minerals form from solutions. Big Idea: Earth’s surface is worn away by physical (mechanical) and chemical weathering. Sediment: rock particles carried & deposited by water, wind, or ice. Sedimentary rock forms as rock weathers physically and/or chemically and is pressed into layers that harden over time. Weathering: breaking down of rocks and other materials on Earth’s surface Physical weathering: breaking down or rocks in which the chemical make-up of the rocks does not change. Example: water freezes & expands in cracks in the rock, breaking it apart. Chemical weathering: breaking down of rocks in which the chemical make-up of the rock changes. Example: Acid rain -- Carbon dioxide in rain forms a weak acid that weaken rocks, buildings, and statues. Examples of sedimentary rock: sandstone, shale, conglomerate, breccia, limestone Hard to classify examples: coal formed from dead plants & animals, coquina formed from seashell fragments & chert formed from tiny shells of marine plankton METAMORPHIC ROCK Big Idea: Metamorphic rocks are formed when existing rocks are changed by heat and pressure. Foliated: texture of a metamorphic rock that has mineral crystals arranged in bands Non-foliated: texture of a metamorphic rock that does NOT have mineral crystals arranged in bands Examples of metamorphic rock: schist, gneiss, slate, marble, anthracite, phyllite ROCK CLASSIFICATION/FORMATION STUDY AID Type of Rock Igneous How Rock Was Formed hot magma cools and hardens Sedimentary sediments are pressed and cemented together or when minerals form from solutions. Over time, pressure hardens the layers. existing rocks are changed by heat and pressure Metamorphic *Examples granite, obsidian, pumice, basalt, andesite, rhyolite sandstone, shale, conglomerate, limestone, breccia gneiss, slate, marble, schist, anthracite, phyllite *Students should be able to identify the italicized rocks. OHIO’S GEOLOGIC HISTORY Coal Formation in Ohio: 300 million years ago, Ohio was near the equator. Lush vegetation grew in warm swamps. When plants died, & were compressed over time, coal was formed. This was mined to create energy by burning it to create heat and steam to run power plants. A shallow sea that once covered Ohio formed sandstone & limestone we have today.