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Discover the wonders of rocks - their formation, classification, and transformation through the rock cycle. From igneous to metamorphic to sedimentary rocks, learn about the processes that shape Earth's surface.
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Rockin’ Science Rocks and Rock Cycle
What is a rock? • Mixture of minerals, volcanic glass, organic or other materials. • There are three types of rocks: • Igneous • Metamorphic • Sedimentary
Igneous • Rocks formed when hot magma cools and hardens. • Magma vs. lava – • Magma is hot, melted rock material beneath Earth’s surface • Lava is magma that reaches the Earth’s surface and flows from volcanoes
Two Types of Igneous Rocks • Intrusive – generally contain large crystals, and forms when magma cools slowly beneath Earth’s surface. • Extrusive – fine-grained, and forms when magma cools quickly at or near Earth’s surface
Further Classification • Another way to identify igneous rocks is by the magma from which they form • Basaltic Rocks – igneous rocks that are dense and dark in color. They form from magma that is rich in iron and magnesium, but poor in silica.
Granitic Rocks • Igneous rocks that have a lower density than basaltic rocks, and are light in color. Granitic magma is thick, stiff and contains lots of silica.
Andesitic Rocks • Igneous rocks that have a mineral composition between basaltic and granitic rocks
Mighty Morphin’ Rocks Metamorphic Rocks
Formation • Metamorphic rocks form when heat, pressure, or fluids act on igneous, sedimentary, or other metamorphic rocks. • The heat and pressure can change the rocks form, composition, or both.
Heat and Pressure… • Rocks beneath Earth’s surface are under great pressure from the layers above them. • Temperature also increases with depth. • The amount of heat and pressure along with the composition of the rock determines what the metamorphic rock will look like.
Hot Fluids • In the presence of hot, water-rich fluids, solid rock can change in mineral composition without having to melt.
Classifying Metamorphic Rocks • Foliated rocks - when mineral grains flatten and line up in parallel layers • Nonfoliated rocks - when mineral grains grow and rearrange but do not form layers.
Sedimentary Rocks And the Rock Cycle
Settlement - Sediment • Sediments are loose rock fragments, mineral grains, and shell that have been moved by wind, water, ice, or gravity. • Sedimentary rocks form when sediments are pressed and cemented together. • They often form layers. The oldest layer of rock is on the bottom.
Classification • Detrital • Chemical • Organic
Detrital • Made of grains of minerals or other rocks. • Other minerals dissolved in water act to cement particles together, and the weight of the sediment above them also squeezes or compacts the layers into rock.
Chemical Rocks • Form when mineral-rich water from geysers, hot springs, or salty lakes evaporate. • Limestone, rock salt, dolostone
Organic Rocks • Rocks made of once living things • Chalk, Coal
