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Rocks
Classifying Rocks
Igneous Rocks
Sedimentary Rocks
Rocks from Reefs
Metamorphic Rocks
The Rock Cycle
Table of Contents
Rocks
• When studying a rock sample, geologists observe the rock’s mineral composition, color, and texture.
Studying Rocks- Classifying Rocks
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
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.
- Classifying Rocks
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
Rocks
Texture• Grain Shape – varies greatly from sand grains to
large triangular grains
• Grain Pattern – can vary also from layers to swirls to bands
- Classifying Rocks
Rocks
How Rocks Form• Geologists classify rocks into three major
groups: – igneous rock, sedimentary rock, and
metamorphic rock.
- Classifying Rocks
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 Rocks
Rocks
Classifying Igneous Rocks• Igneous rocks are classified according to
their origin, texture, and mineral composition.
- Igneous Rocks
Rocks
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
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.
- Igneous Rocks
Rocks
Mineral Mixture
– Feldspar
• Reading Graphs:
– What mineral is most abundant in granite?
- Igneous Rocks
Rocks
Mineral Mixture
– 10%
• Reading Graphs:
– About what percentage of granite is made up of dark minerals?
- Igneous Rocks
Rocks
Mineral Mixture
– 100% - (35% + 10%) = 55%
• 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?
- Igneous Rocks
Rocks
Mineral Mixture
– The overall color would be darker.
• Predicting:
– How would the color of the granite change if it contained less feldspar and more mica and hornblende?
- Igneous Rocks
Rocks
Links on Igneous Rocks
• Click the SciLinks button for links on igneous rocks.
- Igneous Rocks
Rocks
From Sediment to Rock• Most sedimentary rocks are formed
through a series of processes: erosion, deposition, compaction, and cementation.
- Sedimentary Rocks
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
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
- Sedimentary Rocks
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
- Sedimentary Rocks
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.
- Sedimentary Rocks
Peat
Bituminous
Lignite
Anthracite
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.
- Sedimentary Rocks
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.
- Sedimentary Rocks
Rocks
Links on Sedimentary Rocks
• Click the SciLinks button for links on sedimentary rocks.
- Sedimentary Rocks
Rocks
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
- Rocks From Reefs
Rocks
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.
Rocks
More on Coral Landforms
• Click the PHSchool.com button for an activity
about coral landforms.
- Rocks From Reefs
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.
- Metamorphic Rocks
Rocks
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)
- Metamorphic Rocks
Shale
Slate
Gneiss
Rocks
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
- Metamorphic Rocks
Rocks
Links on Metamorphic Rocks
• Click the SciLinks button for links on metamorphic rocks.
- Metamorphic Rocks
Rocks
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
Rocks
• Rock cycle – processes on the surface and inside Earth that slowly change rocks from one kind to another.
- The Rock Cycle
Rocks
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
Rocks
Rock Cycle Activity
• Click the Active Art button to open a browser window and access Active Art
about the rock cycle.
- The Rock Cycle
Rocks
Magma
Rock Cycle
Igneous
Sedimentary
Metamorphic
- The Rock Cycle
Rocks
Rocks
Sedimentary
includeinclude include
can be
IntrusiveNon-
foliatedClastic
Graphic Organizer
Igneous Metamorphic
Extrusive Organic Chemical Foliated