Classifying Rocks SE65 c. Construct an explanation of how to classify rocks by their formation and how rocks change through geologic processes in the rock cycle

Classifying Rocks Rocks are put into 3 categories based on how they form: Igneous Sedimentary Metamorphic

Igneous Rocks Igneous rock forms when hot, liquid rock, or magma, cools and solidifies (hardens) There are two types of igneous rocks: INTRUSIVE and EXTRUSIVE

INTRUSIVE IGNEOUS ROCKS Form when magma is cooled very slowly inside the Earth. The surrounding material acts as an insulator to keep the magma warm. Since the magma takes a long time to cool, the minerals have time to crystallize and grow. These rocks form large crystals. The texture of intrusive rocks is coarse-grained since the mineral crystals are visible.

Granite

Gabbro

Diorite

Andesite

EXTRUSIVE IGNEOUS ROCKS Form when lava is cooled quickly on the surface the Earth. The air and water help cool the lava down very fast. Sometimes the lava cools so fast that air bubbles get trapped in the lava. Since the lava cools so quickly, the minerals don’t have time to crystallize and grow. These rocks form small crystals. The texture of extrusive rocks is fine-grained since the mineral crystals are too small to see.

Pumice

Scoria

Basalt

Metamorphic Rocks Metamorphism means “change shape” Metamorphic rocks are formed by heat and pressure Metamorphic rocks can change many times into other rocks

Textures of Metamorphic Rock Foliated Nonfoliated Mineral grains are arranged in planes or bands Mineral grains are not arranged in planes or bands

Gneiss

Marble

Sedimentary Rocks Formed when sediments of rocks, plants, or animals are cemented together, at or near the Earth’s surface. A sedimentary rocks forms by 5 processes: weathering, erosion, deposition, compaction, and cementation (WEDCC).

W.E.D.C.C. W – WEATHERING (running water or wind breaks rocks into sediments) E – EROSION (running water or wind carries away sediments) D – DEPOSITION (sediment drops out of water or wind) C – COMPACTION (sediments are pressed together) C – CEMENTATION (LITHIFICATION) (sediments are glued together with dissolved minerals)

Chemical – formed when minerals crystallize out of a solution, like water, to form a rock

Limestone

Chert

3 Types of Sedimentary Rock Clastic – made from fragments of rocks cemented together by a mineral

Conglomerate

Sandstone Strata – layers of rock

Organic – formed from the remains of plants and animals Coal

Limestone