Rocks…
There are three types of rocks:
• Igneous - granite
• Metamorphic - gneiss
• Sedimentary - limestone
What’s an igneous rock?!?
• Igneous comes from the Latin ignis, or
“fire”.
• Igneous rocks form as molten rock cools
and solidifies.
• The parent material for igneous rock is
magma…
• … and magma that reaches the Earth’s
surface is called lava.
Igneous rocks are classified into two
groups depending on where they solidify:
• Igneous rocks that form when molten rock
solidifies on the surface are called extrusive,
or volcanic.
• Igneous rocks that form before reaching the
surface are called intrusive, or plutonic.
Magma comes from inside the
Earth…
Igneous rocks are classified in 3
basic categories:
• Granitic
granite rhyolite
• Basaltic
gabbro basalt
• Andesitic
diorite andesite
Granitic rocks…
• Contain a lot of quartz
and feldspar which
give most granitic
rocks their light color.
• Lower density
• Include:
– pumice
– obsidian
Basaltic rocks…
• …are dense and tend
to be
• ...dark in color
• Includes:
– Basalt
– and Scoria
…and the last is Andesitic.
• The crystals are medium to fine grain.
• Color can have a salt and pepper look.
What’s a Sedimentary rock?!?
• Sedimentary comes from the Latin
sedimentum which means “settling”…
• 75% of all rocks on the surface are
sedimentary (…most of the rocks below the
surface are igneous).
• Sedimentary rocks form by the processes of
compaction and cementation.
What makes the sediment?
• First, the weathering of existing rocks begin
the process.
• Next, erosional agents such as running
water, wind, waves, and ice remove the
remains of weathering.
• Sediment gathers and starts to form layers.
• These layers start to stick together and form
solid rock.
Let’s see how sedimentary rock is
formed…
Types of Sedimentary Rocks.
• Detrial or Clastic sedimentary rocks:
– Formed from the accumulation of particles that
are compacted or cemented together.
– Particle size is used to distinguish these types of
rocks.
– Common detrial sedimentary rocks, in order of
size are – shale, sandstone, and conglomerate or
breccia.
Shale
Sandstone
Conglomerate
Breccia
…Types continued…
• Chemical sedimentary rocks:
– Formed when dissolved substances…
• precipitate out of the solution.
• is left when the solution evaporates.
– Examples of chemical sedimentary rocks
include: limestone, chert, rock salt, and
gypsum
– Rock salt and gypsum are called evaporites.
Limestone
Chert
Rock salt
Gypsum
… and finally.
• Organic sedimentary rocks:
– Formed from the remains of once-living (now
dead) things. These include remains of clams,
mussels, coral, and snails.
– The shells of these animals contain calcite, a
major component of rocks.
– Examples include: limestone, coquina, and
chalk.
Metamorphic Rocks…
• Metamorphism means to “change form”.
• ‘Agents’ of metamorphism include:
– Heat
– Pressure (stress)
– Chemically active fluids (like water)
• The degree of metamorphism and
involvement of each agent varies.
The Agents
• Heat – gives energy to cause chemical
changes that result in recrystallization of
mineral.
• Pressure – makes the rock break, shear, or
become plastic (with heat).
• Chemically active fluids – can promote
recrystallization or the formation of
completely new minerals. (ion exchange)
What kind of changes can you see?
• When pressure and heat are just right particles
within the rock can recrystallize and realign.
• This realignment causes the rock to have a
banded or layered texture called foliation.
• Examples include: slate, phyllite, schist,
gneiss.
Foliation…
Nonfoliated texture…
• Some rocks, like those of one mineral,
(limestone) are nonfoliated.
• The small crystals may combine to form larger
interlocking crystals instead.
• Examples include: marble and quartzite
How does metamorphism happen…
The Rock Cycle