ROCKS, ROCKS, AND MORE ROCKS! Chapters 5 and 6 (Glencoe Earth Science)

What is a rock?  A rock is a hard substance made of one or more minerals  There are 3 types of rocks:  Igneous  Sedimentary  Metamorphic

What’s an Igneous Rock?  Formed when magma crystallizes  These rocks are associated with fiery lava flows  Lava is magma that flows on the Earth’s surface

Types of Igneous Rocks  Extrusive  Formed from lava on Earth’s surface that cools quickly  Known as volcanic rock  Fine-grained  Intrusive  Formed inside the Earth  Magma rises up into pre-existing rocks and hardens  Coarse-grained  Called “Plutonic” rocks after Pluto, the god of the Underworld  These rocks commonly produce landforms  Granite is most common

What About Igneous Rocks?  Useful as building materials

It’s Sedimentary, Watson!  What’s a sedimentary rock?  A rock formed from sediments  Sediments are pieces of material that have been carried/deposited by wind, water, ice, gravity, or chemical precipitation.  Sedimentary rocks form when these pieces are cemented together

How do Sedimentary Rocks Form?  Weathering  Processes that break rock into smaller pieces Chemical-minerals in rock are dissolved or chemically changed Physical-minerals are unchanged; rock fragments break off  Erosion  Movement of materials from one location to another Caused by wind, moving water, gravity, glaciers (ice) Eroded materials almost always moved downhill

Sediments, Classified  Clastic Rock  Refers to fragments of rock and minerals created by weathering and erosion  Clastic comes from the Greek word for “broken”  Classified by particle size

Deposition  Occurs when sediments are laid down on the ground or sink to the bottom of a body of water  Largest particles settle first than smallest are last.

Burial  Most sediments are deposited in basins (depressions)  As more sediments are deposited, the layers on the bottom are exposed to more heat and pressure.  Causes lithification  Physical and chemical processes that turn sediment into sedimentary rock

Process of Lithification  1-Compaction  Weight of sediments forces them closer together  Water is squeezed out of mud  Sand resists compaction because of grain-to-grain contact

Process of Lithification  2-Cementation  Temperatures increase  Mineral growth cements sediments together into solid rock

Features of Sedimentary Rock  Horizontal layering (bedding)  Graded bedding: particle size becomes more coarse/heavy toward bottom layers  Cross-bedding: formed as inclined layers of sediment move forward across a horizontal surface  Fossils  Evidence of once-living organisms  These are sedimentary rocks!

Types of Sedimentary Rock (3 Types)  Clastic Rock  Most common; formed from deposits of loose sediments

Types of Sedimentary Rock  Chemical Rocks  Formed when water evaporates leaving minerals behind  Ex: Stalactites (upper), stalagmites (lower)  Organic Sedimentary Rocks  Formed from remains of a once-living thing  Ex: limestone (Calcium Carbonate for seashells)

Why are Sedimentary Rocks Important?  It allows us a “snapshot” of surface conditions in Earth’s past.  Energy Resources  Coal, Oil, Natural gas are found in sedimentary rock  Many metals are mined from sedimentary rocks  Used in making cement (limestone)  Used in making blocks for walls (sandstone, limestone)

Metamorphic Rock  When high temperature and pressure combine to alter the texture, mineralogy, or chemical composition of a rock without melting it.  Metamorphism = Change and form

This high pressure for a rock to become metamorphic can happen in 2 ways: Vertical Pressure caused by the weight of overlying rock Compressive forces generated as rocks are deformed during mountain building.

The Rock Cycle  Continuous changing and remaking of rocks  Rocks are constantly being recycled from one type to another

Example of the Path of a Rock Through the Rock Cycle  Granite (igneous rock)  Wind/rain erodes exposed rock, bits flake off, carried to bottom of stream  carried to river, along with other sediments  carried to sea, deposited  Deposits build up  form sandstone (sedimentary rock)   Sediments continue to be buried and are under more pressure/higher temps  pressed together even more  form quartzite (metamorphic rock)  AND THE CYCLE CONTINUES…