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Rocks

Science, Grade 8

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sandstone (sedimentary) gneiss (metamorphic, foliated) quartzite (metamorphic, nonfoliated) granite (igneous) shale (sedimentary) slate (metamorphic, foliated) Foliated metamorphic rock is arranged in layers. Heat & Pr essure erosion compaction cementation Sedimentary Rocks sandstone conglomerate limestone shale coquina Sedimentary Rocks Sedimentary rocks are rocks that have been placed in layers by weathering or erosion. Over millions of years, these layers are compressed and cemented together. Igneous Rocks Igneous rocks form when liquid rock cools and hardens. Liquid rock that is under the crust is called magma. When it pours out onto the Earth’s surface, it is then called lava. Igneous rocks are classified by their origin, texture and composition. Intrusive igneous rocks originate from cooling magma, while extrusive rocks are made from cooling lava. Texture is related to how long it takes a rock to cool. Slow- cooling rocks form visible crystals, while fast-cooling rocks have small crystals that are not always visible. Dark igneous rocks, described as mafic, have a different composition than light igneous rocks, described as felsic. Granite is a light-colored intrusive rock with visible crystals. Pumice is a lightweight rock made from frothing lava and gases. It is the only rock that can float on water. Basalt forms much of the ocean’s crust. Obsidian is a dark, glassy igneous rock. There are three categories of sedimentary rocks. Clastic sedimentary rocks are composed of pieces of other pre-existing rock. These pre-existing rocks are weathered and transported by water and wind and are re-deposited elsewhere. The sediments accumulate and lithify (become solid rock). Chemical sedimentary rocks are sedimentary rocks that formed through chemical precipitation. Under ideal conditions, dissolved lime in ocean water precipitates out of the water and accumulates on the ocean floor which eventually lithifies into limestone. Biochemical or (organic) sedimentary rocks form when the shell remains of organisms collect on the ocean floor and lithify, becoming fossils and a layer of limestone. Metamorphic Rocks Metamorphic rocks are rocks that have changed as the result of intense heat and pressure deep in the Earth’s crust. Metamorphic rocks are classified as foliated and nonfoliated. Foliated metamorphic rocks such as gneiss, schist and slate have their mineral grains arranged in parallel layers. Nonfoliated metamorphic rocks such as marble and quartzite have their mineral grains arranged randomly. Rocks © Copyright NewPath Learning. All Rights Reserved. 94-4102 www.newpathlearning.com Some photos courtesy of USGS. pumice obsidian granite basalt lava magma

Sedimentary Rocks Sedimentary Rocks What are sedimentary rocks? ___________________________________________________ ___________________________________________________ Igneous Rocks How do igneous rocks form? ________________________ __________________________________________________ __________________________________________________ __________________________________________________ How are igneous rocks classified? ____________________ __________________________________________________ __________________________________________________ Dark igneous rocks are referred to as __________________. Light colored igneous rocks are referred to as __________________________. There are three categories of sedimentary rocks. Clastic sedimentary rocks _______________________________ ______________________________________________________ ______________________________________________________ Chemical sedimentary rocks _____________________________ ______________________________________________________ ______________________________________________________ Biochemical or (organic) sedimentary rocks _______________ ______________________________________________________ ______________________________________________________ Metamorphic Rocks What are metamorphic rocks? _________________________________ _________________________________ _________________________________ Metamorphic rocks are classified as ____________________________ and __________________________ __________________________. Foliated metamorphic rocks _________________________________ _________________________________ Nonfoliated metamorphic rocks _________________________________ _________________________________ Heat & Pr essure • biochemical sedimentary rock • chemical sedimentary rock • clastic sedimentary rock • erosion • felsic • foliated metamorphic rock • igneous rock • lava • mafic • magma • metamorphic rock • nonfoliated metamorphic rock • sedimentary rock • weathering Key Vocabulary Terms Rocks © Copyright NewPath Learning. All Rights Reserved. 94-4102 www.newpathlearning.com Some photos courtesy of USGS. \|xiBAHBDy01793mzV

Rocks

Science, Grade 8

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