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Rockin’ Science
Rocks and Rock Cycle
What is a rock?
• Mixture of minerals, volcanic glass,
organic or other materials.
• There are three types of rocks:
1. Igneous
2. Metamorphic
3. Sedimentary
Igneous
• Rocks formed when hot magma cools
and hardens.
• Magma vs. lava –
– Magma is hot, melted rock material
beneath Earth’s surface
– Lava is magma that reaches the Earth’s
surface and flows from volcanoes
Two Types of Igneous Rocks
• Intrusive – generally contain large
crystals, and forms when magma cools
slowly beneath Earth’s surface.
• Extrusive – fine-grained, and forms
when magma cools quickly at or near
Earth’s surface
Further Classification
• Another way to identify igneous rocks
is by the magma from which they form
• Basaltic Rocks – igneous rocks that are
dense and dark in color. They form
from magma that is rich in iron and
magnesium, but poor in silica.
Granitic Rocks
• Igneous rocks that have a lower
density than basaltic rocks, and are
light in color. Granitic magma is thick,
stiff and contains lots of silica.
Andesitic Rocks
• Igneous rocks that have a mineral
composition between basaltic and
granitic rocks
Mighty Morphin’ Rocks
Metamorphic Rocks
Formation
• Metamorphic rocks form when heat,
pressure, or fluids act on igneous,
sedimentary, or other metamorphic
rocks.
• The heat and pressure can change the
rocks form, composition, or both.
Heat and Pressure…
• Rocks beneath Earth’s surface are
under great pressure from the layers
above them.
• Temperature also increases with
depth.
• The amount of heat and pressure along
with the composition of the rock
determines what the metamorphic
rock will look like.
Type of Rock Before
Type of Rock After
(metamorphic)
Granite/Igneous
Gneiss
Sandstone/
Sedimentary
Quartzite
Limestone/
Sedimentary
Marble
Hot Fluids
• In the presence of hot, water-rich
fluids, solid rock can change in mineral
composition without having to melt.
Classifying Metamorphic Rocks
• Foliated rocks - when mineral grains
flatten and line up in parallel layers
• Nonfoliated rocks - when mineral
grains grow and rearrange but do not
form layers.
Examples of Foliated Rocks…
Examples of Nonfoliated Rocks…
Sedimentary Rocks
And the Rock Cycle
Settlement - Sediment
• Sediments are loose rock fragments,
mineral grains, and shell that have
been moved by wind, water, ice, or
gravity.
• Sedimentary rocks form when
sediments are pressed and cemented
together.
• They often form layers. The oldest
layer of rock is on the bottom.
Classification
• Detrital
• Chemical
• Organic
Detrital
• Made of grains of minerals or other
rocks.
• Other minerals dissolved in water act
to cement particles together, and the
weight of the sediment above them
also squeezes or compacts the layers
into rock.
Detrital Rocks
Chemical Rocks
• Form when mineral-rich water from
geysers, hot springs, or salty lakes
evaporate.
• Limestone, rock salt, dolostone
Organic Rocks
• Rocks made of once living things
• Chalk, Coal
Rock Cycle