Chapter 6: RocksChapter 6: Rocks
Chapter 6.1Chapter 6.1
How Rocks FormHow Rocks Form
What Is A Rock?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 CycleThe Rock Cycle
• Classifies the rocks of the crust according to their origin
Chapter 6.2Chapter 6.2
Igneous RockIgneous Rock
Igneous Rock FormationIgneous 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 FormedWhere 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 DescriptionsIgneous 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 6.3Chapter 6.3
Sedimentary RockSedimentary Rock
– Formed from the compacting and cementing of sediments
Clastic Sedimentary RockClastic 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 RockChemical Sedimentary Rock
• These rocks form when minerals precipitate or falling out of a solution– Rock salt (halite), gypsum and some
limestone
Organic Sedimentary RockOrganic Sedimentary Rock
• Consists of sediments from the remains of plants and animals– Coal and limestone (shells)
Features of Sedimentary RockFeatures 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 6.4Chapter 6.4
Metamorphic RockMetamorphic Rock
– Formed from pre-existing rock (parent rock)
Metamorphism – rocks structure is Metamorphism – rocks structure is changed by pressure, heat and moisturechanged 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 Metamorphic Rock DescriptionsDescriptions
• Foliation – tendency of rocks to form layers with visible minerals
• Non foliated –– Banded – light and dark colors– Non-organized –
• Sandstone quartzite • Limestone marble
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