Table of Contents Classifying Rocks Igneous Rocks Sedimentary Rocks Rocks from Reefs Metamorphic Rocks The Rock Cycle

- Classifying Rocks Studying Rocks When studying a rock sample, geologists observe the rock’s mineral composition, color, and texture.

Mineral Composition and Color - Classifying Rocks Mineral Composition and Color Rock – a solid mixture of minerals and other materials. Rock-forming minerals – the common minerals that make up most of the rocks of Earth’s crust. Granite – tends to be a light-colored rock that has high silica content Basalt – tends to be a dark-colored rock that is low in silica

- Classifying Rocks Texture Grains – particles of minerals or other rocks that give a rock its texture. Texture – the look and feel of a rock’s surface, determined by the size, shape, and pattern of a rock’s grains.

Texture Grain size Coarse-grained – large easy to see grains - Classifying Rocks Texture Grain size Coarse-grained – large easy to see grains Fine-grained – so small they can only be seen under a microscope

- Classifying Rocks Texture Grain Shape – varies greatly from sand grains to large triangular grains Grain Pattern – can vary also from layers to swirls to bands

How Rocks Form Geologists classify rocks into three major groups: - Classifying Rocks How Rocks Form Geologists classify rocks into three major groups: igneous rock, sedimentary rock, and metamorphic rock.

- Classifying Rocks How Rocks Form Igneous rock – type of rock that forms from the melting then cooling of molten rock at or below the surface. Sedimentary rock – type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together. Metamorphic rock – type of rock that forms from an existing rock that is changed by heat and pressure

Classifying Igneous Rocks Igneous rocks are classified according to their origin, texture, and mineral composition.

Classifying Igneous Rocks Extrusive igneous rock – forms from lava on Earth’s surface. Intrusive igneous rock – forms when magma hardens beneath Earth’s surface. The faster igneous rock cools, the finer the grains Extrusive igneous rock tends to be a finer-grained rock than intrusive igneous rock

- Igneous Rocks Mineral Mixture Granite is a mixture of light-colored minerals, such as feldspar and quartz, and dark-colored minerals, including hornblende and different types of mica. But granite can vary in mineral composition. This affects its color and texture.

Mineral Mixture Reading Graphs: - Igneous Rocks Mineral Mixture Reading Graphs: What mineral is most abundant in granite? Feldspar

Mineral Mixture Reading Graphs: - Igneous Rocks Mineral Mixture Reading Graphs: About what percentage of granite is made up of dark minerals? 10%

Mineral Mixture Calculating: - Igneous Rocks Mineral Mixture Calculating: If the amount of quartz increases to 35 percent and the amount of dark-colored minerals stays the same, what percentage of the granite will be made up of feldspar? 100% - (35% + 10%) = 55%

Mineral Mixture Predicting: - Igneous Rocks Mineral Mixture Predicting: How would the color of the granite change if it contained less feldspar and more mica and hornblende? The overall color would be darker.

Click the SciLinks button for links on igneous rocks.

- Sedimentary Rocks From Sediment to Rock Most sedimentary rocks are formed through a series of processes: erosion, deposition, compaction, and cementation.

- Sedimentary Rocks From Sediment to Rock Sediment – small, solid pieces of material that come from rocks or organisms. Usually forms due to erosion Erosion – a destructive process in which water or wind loosens and carries away fragments of rock. Deposition – process by which sediment settles out of the water or wind that is carrying it.

- Sedimentary Rocks From Sediment to Rock Compaction – process by which sediments are pressed together under their own weight. Occurs over millions of years as layers build Cementation – process by which dissolved minerals crystallize and glue particles of sediment together into one mass. Takes place when sediment is in the presence of water

Types of Sedimentary Rock - Sedimentary Rocks Types of Sedimentary Rock There are three major groups of sedimentary rocks: clastic rocks, organic rocks, and chemical rocks. Clastic rock – sedimentary rock that forms when rock fragments are squeezed together under high pressure. Can range in size from microscopic clay particles to large boulders Ex: shale, sandstone, conglomerate, and breccia

Types of Sedimentary Rock - Sedimentary Rocks Types of Sedimentary Rock Organic rock – sedimentary rock that forms from remains of organisms deposited in thick layers. Ex: Coal and Limestone Coal forms from the remains of swamp plants buried in water. Limestone forms in the ocean, where many living things, such as coral, clams, and oysters, have hard shells made of calcite that collect on the ocean floor. Peat Lignite Bituminous Anthracite

Types of Sedimentary Rock - Sedimentary Rocks Types of Sedimentary Rock Chemical rock – sedimentary rock that forms when minerals crystallize from a solution. (Reacts to HCl) Ex: Limestone forms from calcite deposits dissolved in lakes, rivers, streams.

Uses of Sedimentary Rock - Sedimentary Rocks Uses of Sedimentary Rock Sedimentary rock has been used for thousands of years in building structures, tools, and statues. Ex: The White House in Washington D.C. is constructed of sandstone.

Links on Sedimentary Rocks Click the SciLinks button for links on sedimentary rocks.

- Rocks From Reefs Coral Reefs Coral reef – a structure of calcite skeletons built up by coral animals in warm, shallow ocean water. When coral animals die, their skeletons remain. More corals build on top of them, gradually forming a coral reef. Only form in ocean water between 30°N and 30°S latitude

Coral Reefs(not in notes) Coral reef is really organic(from living things) limestone. Deposits of organic limestone help geologists figure out what the environment was like long ago. If they find a fossil of coral reef, they would know that location used to contain warm, shallow ocean water.

More on Coral Landforms - Rocks From Reefs More on Coral Landforms Click the PHSchool.com button for an activity about coral landforms.

- Metamorphic Rocks Metamorphic Rock Metamorphic rock – forms when heat and pressure beneath Earth’s surface changes the appearance, texture, crystal structure, and mineral content of either igneous, sedimentary, or other metamorphic rock.

Types of Metamorphic Rocks Geologists classify metamorphic rocks according to the arrangement of the grains that make up the rocks. Foliated rocks – metamorphic rocks that have grains arranged in parallel layers or bands. Ex: Slate – metamorphic shale (denser and more compact than shale) Shale Slate Gneiss

Types of Metamorphic Rocks Nonfoliated rocks – metamorphic rocks that have randomly arranged metamorphic grains that do not split into layers Ex: Quartzite – metamorphic sandstone Marble – metamorphic limestone

Links on Metamorphic Rocks Click the SciLinks button for links on metamorphic rocks.

A Cycle of Many Pathways - The Rock Cycle A Cycle of Many Pathways Forces deep inside Earth and at the surface produce a slow cycle that builds, destroys, and changes the rocks in the crust.

- The Rock Cycle Rock cycle – processes on the surface and inside Earth that slowly change rocks from one kind to another.

The Rock Cycle and Plate Tectonics Plate movements start the rock cycle by helping to form magma, the source of igneous rocks. Plate movements also cause faulting, folding, and other motions of the crust that help to form sedimentary and metamorphic rocks.

- The Rock Cycle Rock Cycle Activity Click the Active Art button to open a browser window and access Active Art about the rock cycle.

- The Rock Cycle Metamorphic Igneous Sedimentary

Graphic Organizer Igneous Metamorphic Extrusive Organic Chemical Foliated