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 Within those groups, rocks can be classified further by their composition and texture.

Composition – the minerals that make up the rock

Texture Texture – the size, shape, and positions of the grains that make up a rock

Igneous Rocks Igneous rock forms when hot, liquid rock, or magma, cools and solidifies (hardens) Igneous rocks are classified by their composition and texture

Composition felsic mafic Felsic – these igneous rocks are lighter in color, less dense, and are rich in aluminum, potassium, silicon, and sodium. Mafic – these igneous rocks are darker in color, denser, and are rich in calcium, iron, and magnesium. felsic mafic

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

An easy way to remember how a sedimentary rocks is WEDCC Sedimentary rocks make up ¾ of the Earth’s rocks Rocks break down into sediments through weathering. These sediments move from one place to another and are deposited in layers (strata). Over a long period of time, these layers get covered by more sediment and become compacted. Dissolved minerals, such as calcite and quartz, act as a cement that binds the sediments together. An easy way to remember how a sedimentary rocks is 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)

3 Types of Sedimentary Rock Clastic – made from fragments of rocks cemented together by a mineral Classified by its fragment sizes Fine-grained Medium-grained Coarse-grained

Conglomerate

Sandstone Strata – layers of rock

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

Chert

Organic – formed from the remains of plants and animals Examples include limestone and coal https://youtu.be/U8Y3oaYR-3c

Limestone

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

How does metamorphism occur? Contact Metamorphism Magma heats surrounding rock and changes it Regional Metamorphism Pressure builds up in rock that is buried below other rock formations Pieces of Earth’s crust collide with each other

Textures of Metamorphic Rock Foliated Nonfoliated Mineral grains are arranged in planes or bands Mineral grains are not arranged in planes or bands Commonly made of one or only a few minerals The crystals change in size or composition called recrystallization

Gneiss

Schist

Quartzite

Novaculite

Structures Deformation – change in shape of a rock caused by a force placed on it Causes folds, or bends https://youtu.be/ za_B_c5v1CA