ROCK NOTES
Big Idea: Igneous, metamorphic, and sedimentary rocks formed
in different ways. Rocks of each type have unique characteristics
that can be used to identify them.
 Rock: mixture of minerals, usually cemented together
Rocks
Igneous
Intrusive
Sedimentary
Extrusive
Metamorphic
Foliated
Nonfoliated
IGNEOUS ROCK
Big Idea: Igneous rocks form when hot magma cools and
hardens.
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Molten rock: melted minerals
Magma: molten rock inside Earth
Lava: magma that reaches Earth’s surface
Intrusive: igneous rock that forms slowly from magma
cooling below the surface. Intrusive rocks are only at
Earth’s surface if forces such as erosion, volcanoes,
landslides, or earthquakes expose them. Examples: granite
 Extrusive: igneous rock that form as lava cools on Earth’s
surface. Examples: rhyolite, basalt, obsidian, pumice,
andesite
SEDIMENTARY ROCK
Big Idea: Sedimentary rocks form when sediments are pressed
and cemented together or when minerals form from solutions.
Big Idea: Earth’s surface is worn away by physical (mechanical)
and chemical weathering.
 Sediment: rock particles carried & deposited by water,
wind, or ice.
 Sedimentary rock forms as rock weathers physically and/or
chemically and is pressed into layers that harden over time.
 Weathering: breaking down of rocks and other materials
on Earth’s surface
 Physical weathering: breaking down or rocks in which
the chemical make-up of the rocks does not change.
Example: water freezes & expands in cracks in the rock,
breaking it apart.
 Chemical weathering: breaking down of rocks in which
the chemical make-up of the rock changes. Example: Acid
rain -- Carbon dioxide in rain forms a weak acid that weaken
rocks, buildings, and statues.
 Examples of sedimentary rock: sandstone, shale,
conglomerate, breccia, limestone
 Hard to classify examples: coal formed from dead plants &
animals, coquina formed from seashell fragments & chert
formed from tiny shells of marine plankton
METAMORPHIC ROCK
Big Idea: Metamorphic rocks are formed when existing rocks are
changed by heat and pressure.
 Foliated: texture of a metamorphic rock that has mineral
crystals arranged in bands
 Non-foliated: texture of a metamorphic rock that does
NOT have mineral crystals arranged in bands
 Examples of metamorphic rock: schist, gneiss, slate,
marble, anthracite, phyllite
ROCK CLASSIFICATION/FORMATION STUDY AID
Type of Rock
Igneous
How Rock Was Formed
hot magma cools and
hardens
Sedimentary
sediments are pressed
and cemented together
or when minerals form
from solutions. Over
time, pressure hardens
the layers.
existing rocks are
changed by heat and
pressure
Metamorphic
*Examples
granite, obsidian,
pumice, basalt,
andesite, rhyolite
sandstone, shale,
conglomerate,
limestone, breccia
gneiss, slate, marble,
schist, anthracite,
phyllite
*Students should be able to identify the italicized rocks.
OHIO’S GEOLOGIC HISTORY
 Coal Formation in Ohio: 300 million years ago, Ohio was
near the equator. Lush vegetation grew in warm swamps.
When plants died, & were compressed over time, coal was
formed. This was mined to create energy by burning it to
create heat and steam to run power plants.
 A shallow sea that once covered Ohio formed sandstone &
limestone we have today.
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