Rocks 8 th grade Earth Science Classifying Rocks

Rocks 8 th grade Earth Science

Classifying Rocks Mineral Composition – rocks are made of mixtures of minerals and other materials. Some contain a single mineral. Others contain several minerals. l Color – color provides clues to the rock’s mineral composition. (Ex: granite = light basalt = dark) l Texture – the look and feel of the rock’s surface. They use shape, size and pattern. l Origin – how the rock is formed. l

3 Types of Rocks l There are 3 major groups of rocks: l Igneous Sedimentary Metamorphic l l

Igneous Rocks l l l The name igneous comes from a Latin word meaning “fire”. Igneous rocks can be either intrusive or extrusive rock. Extrusive – formed from lava that erupted onto the Earth’s surface. Basalt is the most common extrusive rock. Intrusive – formed from magma that hardens beneath the Earth’s surface. Granite is the most common intrusive rock.

Igneous Rocks Obsidian extrusive Granite intrusive

Sedimentary Rocks l Sedimentary rocks are formed through a series of processes: l Erosion Deposition Compaction Cementation l l l

Sedimentary Rocks l l Erosion – water, wind or ice loosen and carry away fragments of rock. Deposition – sediment settles out of the water or wind carrying it. Compaction – process that presses the sediments together. Cementation – dissolved minerals crystallize and glue particles of sediment together.

Types of Sedimentary Rocks l There are 3 major groups of sedimentary rocks: l Clastic – forms when rock fragments are squeezed together. Organic – remains of plants or animals are deposited in thick layers. Chemical – when minerals that are dissolved in a solution crystallize. l l

Sedimentary Rocks l Clastic sandstone l Organic coal l Chemical limestone

Metamorphic Rocks l Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock. l Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks.

Metamorphic Rocks l There are 2 classifications for metamorphic rocks: l Foliated – have their grains arranged in parallel layers or bands. l Nonfoliated – mineral grains are arranged randomly. They do not split into layers.

Metamorphic Rocks l Foliated gneiss l Nonfoliated quartzite

The Rock Cycle l The rock cycle is the series of processes on Earth’s surface and in the crust and mantle that slowly change rocks from one kind to another.