Download Chapter 6: Rocks

Chapter 6: Rocks
Chapter 6.1
How Rocks Form
What Is A Rock?
• Rock is a group of minerals bound
together.
• Rocks are classified by the processes
that they form under.
– Igneous – formed from the cooling of hot
molten rock
– Sedimentary – formed by the compaction and
cementation of sediments
– Metamorphic – formed the heat and pressure
on pre-existing rock
The Rock Cycle
• Classifies the rocks of the crust
according to their origin
Chapter 6.2
Igneous Rock
Igneous Rock Formation
• Felsic Magma
– Very thick and slow moving
– Contains large amounts of silica
– Light-colored minerals quartz and orthoclase
feldspar
• Mafic Magma
– Hotter and more fluid
– Contains large amounts of iron and
magnesium
– Formed dark silicate minerals hornblende
augite and biotite
Where Formed
• Underground magma
– Cools slower which allows larger gains known
as a coarse texture
• At the surface
– Cools fast minerals are microscopic of
nonexistent
– Small crystals considered fine grain texture
– No crystals considered glassy texture
– Porphyry – texture where large crystals are
surrounded by a fine-grained mass rock
Igneous Rock Descriptions
– Igneous rocks are grouped into families
according to their mineral composition
• Granite Family
– Form from felsic magma
– Granite itself is the intrusive coarse-grained member
of this family that is found in many mountainous areas
in the U.S.
– Obsidian – chemical composition resembles
granite but has a glassy texture and dark color
– Pumice – contains a many air holes and has a
glassy texture
– Rhyolite – fine grain igneous rock that is light in
color
• Gabbro Family
– Form from mafic magma
– Gabbro itself is a coarse-grained dark igneous
rock
– Basalt – the most common it is fine grained
– Scoria – glassy texture with air holes
• Diorite Family
– Neither felsic nor mafic
– Intermediate in color grays to green
– Diorite – coarse grain
– Andosite – fine grain
• Igneous Intrusions
– Pluton – a rock mass that forms when magma
cools inside Earth’s interior
– Dykes – Pluton of Igneous sheet rock that
cuts across rock layers
– Sill – Pluton of Igneous sheet rock that lies
parallel to the rock layers
– Batholiths – the largest plutons form the core
the mountain ranges
Chapter 6.3
Sedimentary Rock
– Formed from the compacting and
cementing of sediments
Clastic Sedimentary Rock
• Formed from fragments of other rock
• Formations of clastics begins with the
movement and relocation of fragments
• Usually transported by running water
which deposits them into a body of
water
– River – bay
• The lighter the material the farther from
shore they are carried
– Particles are sorted by size
– The largest gravels fall out 1st forming
conglomerates followed by sands then
clays
• The particles of the rocks become
cemented together
– Silica cements are more durable than calcite
cements
Chemical Sedimentary Rock
• These rocks form when minerals
precipitate or falling out of a solution
– Rock salt (halite), gypsum and some
limestone
Organic Sedimentary Rock
• Consists of sediments from the
remains of plants and animals
– Coal and limestone (shells)
Features of Sedimentary
Rock
• Stratification – arrangement of visible layers
• Bedding Plane – line between different layers of
rock
• Fossils – round only in Sedimentary rock it is the
remains, impression or any evidence (tracks) of
a plant or animals
• Ripple marks
• Nodules – fine grain silica found in limestone
• Geodes – spheres of silica rock found in
sandstone
Chapter 6.4
Metamorphic Rock
– Formed from pre-existing rock (parent
rock)
Metamorphism – rocks structure is
changed by pressure, heat and moisture
• Regional Metamorphism – occurs in mountain
building areas
– The more pressure and the higher the
temperatures – higher the morph
• Local Metamorphism –
– Contact – where magma touches existing rock
• Shale becomes horn fells which is dense and
fine grained rock
– Deformation – occurs along fault lines where the
heated created by friction cause the rock to
change
Metamorphic Rock
Descriptions
• Foliation – tendency of rocks to form
layers with visible minerals
• Non foliated –
– Banded – light and dark colors
– Non-organized –
• Sandstone  quartzite
• Limestone  marble