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Rocks
The Rock Cycle
Interactions between
water, air and land
can cause rocks to
change from one
form to another.
This process is called
the ROCK CYCLE.
The Rock Cycle – the basics
• Rocks are broken into small pieces (sediment)
• Sediment gets cemented together (makes
different rocks)
• Rocks get subjected to a lot of heat and pressure
(makes different rocks)
• Magma and lava cool (makes different rocks)
Types of Rocks
Rocks – any naturally occuring solid mass of
mineral or mineral-like material
Igneous Rocks
Metamorphic Rocks
Sedimentary Rocks
Sedimentary Rocks
How They are Made
1.
2.
3.
4.
Wind and water break down the earth
Bits of earth settle in lakes and rivers
Layers are formed and build up
Pressure and time turn the layers to rock
Types of Sedimentary Rocks
Sandstone
Limestone
Gypsum
Conglomerate
Shale
Sedimentary Rock: Formation
• Weathering – breaks rock into sediments
• Erosion – weathering combined with movement
of rock sediment (Water, wind, ice, gravity)
• Deposition – process of sediment being moved by
an element of erosion to another place
• Compaction – sediments are squeezed together
• Cementation – dissolved minerals fill in the
spaces between sediments
Sedimentary Rock: Classification
• Clastic – made from weathered bits of rock
and grouped according to the size of
sediments in the rock EX. Shale and Breccia
• Chemical – made from dissolved minerals
“falling” out of solution. This usually happens
when water evaporates. EX. Limestone and
Rock Salt
Metamorphic Rocks
What are They?
1. Rocks that have changed
2. They were once igneous or sedimentary
3. Pressure and heat changed the rocks
Types of Metamorphic Rocks
Schist
Gneiss
Metamorphic Rock: Formation
• Occurs when temperature and pressure are
high in the Earth’s surface and mantle
• Contact Metamorphism – magma intrudes
into existing rock, changes in the rock occur
where the magma touches the existing rock
• Regional Metamorphism – mountain building
– large scale changes
• Agents of Metamorphism – heat, pressure,
reaction to water
Metamorphic Rocks: Classification
• Foliated – layered looking. These layers have
different densities EX. Shale
• Non-foliated – no layers or bands. Usually
have only one mineral EX. Marble
Igneous Rocks
What are They?
1. Fire Rocks
2. Formed underground by trapped, cooled
magma
3. Formed above ground when volcanoes
erupt and magma cools
Types of Igneous Rocks
Granite
Scoria
Pumice
Obsidian
Classification: Igneous Rocks
• Intrusive – made beneath the Earth’s surface
(from magma)
• Extrusive – made above the Earth’s surface
(from lava)
• REMEMBER – magma and lava are the same
thing. Except we call magma lave when it
reaches the Earth’s Surface
Classification: Igneous Rocks - cont
• Course-grained texture – large crystals, slow
cooling
• Fine-grained texture – small crystals, fast
cooling
• Glassy texture– little to no crystals, crazy fast
cooling
• Porphyritic texture – large and small crystals
due to cooling that occurs over thousands of
years
Igneous Rock Composition
• Granitic – makes up continental crust
• Basaltic – makes up the ocean floor
These rocks are made of different concentrations of materials
like silicate.
Granitic - high silicate concentration.
Basaltic - low silicate concentration.
These differences effect rock density. Rock density determines how
plates of rock move. Important for when we talk about Plate
Tectonics.