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
Texture Rate at which magma cools Fine-grained –these crystals are very small or non- existent, and formed by fast-cooling of lava. Coarse – grained – these crystals are large, and formed by the slow-cooling of magma.
https://youtu.be/Uvft8XI4nao Types of Igneous Rocks Intrusive Igneous Rock – rock that forms when magma intrudes (pushes into) surrounding rock below Earth’s surface and cools Extrusive Igneous Rock – rock that forms when magma erupts, or extrudes, onto Earth’s surface and cools https://youtu.be/Uvft8XI4nao
Granite
Gabbro
Diorite
Andesite
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
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