Inside Earth Chapter 5 Notes: Rocks http://www.indiana.edu/~g103/G103/ wk3/wk3.html
site on rocks with crystallization demo (need 3-D glasses for one section) http://www.youtube.com/watch?v=fC
GrXtdSv2c

Section 1: How Do Geologists
Classify Rocks?
• When studying a rock sample, geologists observe the rock’s color and texture and determine its mineral composition

What Is Texture?
• Texture – the look and feel of the rock’s surface
• Most rocks are made up of grains
– particles of minerals or other rocks
• A rock’s grain gives it its texture

How Do Geologists Describe a
Rock’s Texture?
• Terms:
–Grain size
–Grain shape
–Grain pattern

How Does Grain Size Help
Identify a Rock?
• If the grains in a rock are large and easy to see they are said to be coarse-grained
• If the grains are small they are said to be fine-grained

How Does Grain Shape Help
Identify a Rock?
• Different rocks have different grain shapes
– some are smooth while others are jagged

How Does Grain Pattern Help
Identify a Rock?
• The grains in a rock form patterns ;
Some are flat others are wavy

What Does It Mean to Have No
Visible Grain?
• Some rocks cool so quickly they have no crystal grains glassy
• Ex.
Flint

What Do Geologists Do When Texture
Does Not Give Them Enough
Information About a Rock?
• They look at the mineral’s composition under a microscope
–A small sliver of rock allows them to see the shape and size of the crystals
• They use mineral tests too -
Scratch test, acid test, or a magnet

What Are the Major Groups of Rocks?
•
Igneous
•
Sedimentary
•
Metamorphic

How Are Igneous Rocks Formed?
• Igneous – forms from the cooling of molten rock – either magma below the surface or lava at the surface

How Are Sedimentary Rocks
Formed?
• Sedimentary – forms when particles of other rocks or the remains of plants and animals are pressed and cemented together

How Are Metamorphic Rocks
Formed?
• Metamorphic – formed when an existing rock is changed by heat , pressure , or chemical reactions
• Most of these rocks are formed underground

Section 2: Igneous Rocks
What Characteristics Are Used to Classify Igneous Rock?
•
•
•

Where Do Igneous Rocks Come
From?
• Origin – where they are formed
–
Extrusive
– rock that has erupted on to earth’s surface ex. Basalt
–
Intrusive
– rock that formed when magma hardened beneath earth’s surface ex. Granite

What Is the Texture of Igneous
Rock Like?
• Texture depends on the size and shape of the mineral crystals – can have large or small crystals
• Porphyritic Texture – a rock with large crystals scattered on a background of much smaller crystals

What is the Mineral Composition of an Igneous Rock?
• Igneous Rocks differ in mineral composition depending on how much silica and other minerals are present in magma and lava
• Higher silica forms lightcolored rocks like granite
• Lower silica forms dark-colored rocks like basalt

How are Igneous Rocks Used?
• Tools – obsidian was used to make ancient tools
•
Building
– Granite structures
• Basalt is used to make gravel in construction
•
Pumice is used for cleaning and polishing

Section 3:Sedimentary Rocks
What Makes up Sedimentary Rock?
• Sediment – small, solid pieces of material that come from rocks or living things

What Turns These
Sediments Into Solid Rock?
•
•
•
•

What Is Erosion?
• Destructive forces break up and wear away the rock on the earth’s surface
• Occurs when running water or wind loosen and carry away fragments of rock

What Is Deposition?
• The process by which sediment settles out of the water or wind carrying it
• Sediment can include shells , bones, and leaves. Over time the remains of living things may harden and change into fossils

What Is Compaction and
Cementation?
• Compaction – the process that presses sediments together
• Cementation – the process by which dissolved materials crystallize and glue particles of sediment together

What Are the Types of
Sedimentary Rocks?
•
Clastic rocks
•
Organic rocks
•
Chemical rocks

What Is a Clastic Rock?
• A sedimentary rock that forms when rock fragments are squeezed together
• Ex.
Shale , sandstone, and conglomerate

What Are Organic Rocks?
• Rocks that are formed where the remains of plants and animals are deposited in thick layers
• Ex.
Coal , and limestone ( chalk )

What Are Chemical Rocks?
• Rocks that form when minerals that are dissolved in a solution crystallize
• Ex. Rock salt is a chemical rock made up of the mineral halite

Chapel of Saint Kinga the largest among underground chapels in the Wieliczka (Krakow, Poland) Salt mine, is actually a sizable subterranean church carved in rock salt and embellished with salty sculptures and bas-reliefs.

How Is Sedimentary Rock Used?
• Building materials – sandstone ( White House ) and limestone

Section 4: Rocks from Reefs
What is a Coral Reef?
• A structure of calcite skeletons built up by coral animals in warm, shallow ocean water

How Does a Coral Reef Form?
• Coral animals absorb calcium from the ocean water. The calcium is then changed into calcite and forms their shells.
• When an animal dies, their skeleton remains and more corals build on top of them

What Are the Types of Coral
Reefs?
•
Fringing reefs
– close to shore
•
Barrier reefs
– farther out from land
•
Atolls
– ringshaped coral island

How Can Limestone Be Found
Above the Ocean Floor?
•
Limestone that begun as coral can be found on continents in places where uplift has raised ancient sea floors above sea level
Ex. El Capitan, Texas

Section 5: Metamorphic Rocks How Do
Metamorphic Rocks Form?
• Heat and pressure deep beneath earth’s surface can change any rock into metamorphic rock
•
Granite to Gneiss

How Do You Classify Metamorphic
9
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0 x t
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6
4
5
3
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Rocks?
2
• The arrangement of the grains that make up the rocks
– metamorphic rocks can be foliated or nonfoliated
Shale
(sedimentary)
8
7 • Foliated – metamorphic rocks whose grains are arranged in parallel layers or bands ex.
Slate
(metamorphic)
Slate

How Is Metamorphic Rock
Used?
• Most useful metamorphic rocks: marble and slate
• Uses: buildings and statues

Section 6: The Rock Cycle
What Is the Rock Cycle?
• A series of processes on
Earth’s surface and inside the planet slowly change rocks from one kind to another

What Drives the Rock Cycle?
• Convection currents within the mantle cause the plates to move pushing rock back into the mantle

What is the role of plate tectonics in the rock cycle?
• Plate movements start the rock cycle by help to form magma (the source of igneous rocks) and cause faulting, folding, and other motions of the crust that help to form sedimentary and metamorphic rocks.