Chapter Two: Rocks: Materials of the Lithosphere
Chapter Two Learning Objectives:
Chapter Two Outline:
Rock Cycle
Shows the relations among the three rock types
Proposed by James Hutton in the late 1700's
The cycle
Magma
Crystallization
Igneous rock
Weathering
Transportation
Deposition
Sediment
Lithification
Sedimentary Rock
Metamorphism
Metamorphic rock
Melting
Magma
Rock Cycle continued
Full cycle does not always take place due to " shortcuts " or interruptions
Sedimentary rock melts
Igneous rock is metamorphosed
Sedimentary rock weathers
Metamorphic rock weathers
Igneous Rock
Forms as magma cools and crystallizes
Rocks formed inside Earth are called plutonic or intrusive rocks
Rocks formed on the surface
Formed from lava (a material similar to magma, but without gas)
Called volcanic or extrusive rocks
Igneous rock continued
Crystallization of magma
Ions are arranged into orderly patterns
Crystal size of the rock is determined by the rate of cooling
Slow rate forms large crystals
Fast rate forms microscopic crystals
Very fast rate forms glass
Igneous rock continued
Classification is based on the rock's texture and mineral composition
Texture
Size and arrangement of crystals
Types
Fine-grained ----- fast rate of cooling
Coarse - grained ------ slow rate of cooling
Porphyritic ( two crystal sizes ) -- two rates of cooling
Glassy ----- very fast rate of cooling
Igneous rock continued
Mineral composition
Explained by Bowen's reaction series which shows the order of mineral crystallization
Influenced by crystal settling in the magma
Naming Igneous Rocks
Basaltic rocks
Derived from the first minerals to crystallize
Rich in iron and magnesium
Low in silica
Common rock is basalt
Granite rocks
From the last minerals to crystallize
Mainly feldspar and quartz
High silica content
Common rock is granite
Sedimentary rocks
Form from sediments (
weathered products )Form about 75 % of the rock outcrops on the continents
Used to construct much of Earth's history
Clues to past fossils
Provide information about sediment transport
Rocks often contain fossils
Economic importance
Coal
Petroleum and natural gas
Source of iron and aluminum
Classification
Two groups based on the source of the materialsDetrital rocks
Material is solid particles
Classified by particle size
Common rocks are:
Shale ( most abundant)
Sandstone
Conglomerate
Siltstone
Classification continued
Chemical rocksDerived from material that was once in solution and precipitates to form sediment
Directly precipitated or
Through life processes (bio-chemical origin)
Common Rocks
Limestone - the most abundant chemical rock
Travertine
Microcrystalline quartz
Chert
Flint
Jasper
Agate
Evaporates
Rock salt
Gypsum
Coal
Lignite
Bituminous
Produced through lithification
Loose sediments are transformed into solid rock
Lithification processes
Compaction
Cementation by the materials
Calcite
Silica
Iron oxide
FEATURES
Strata, or beds(most characteristic)
Bedding planes separate strata
Fossils
Traces or remains of prehistoric life
Are the most important inclusions
Help determine past environments
Used as time indicators
Used for matching rocks from different places
Metamorphic rocks
"Changed form" rocks
Can form from
Igneous rocks
Sedimentary rocks
Other metamorphic rocks
Degrees of metamorphism
Show in the rock's texture and mineralogy
Types
Low - grade ( e.g., shale becomes slate )
High - grade ( causes the original features to be obliterated )
Metamorphic settings
Regional metamorphism
Over extensive areas
Produces the greatest volume of metamorphic rock
Contact metamorphism
Near a mass of magma
" Bakes " the surrounding rock
Metamorphic agents
HeatPressure
From burial
From stress
Chemically active fluids
Water (most common fluid)
Ion exchange among minerals
Textures
Foliated
Minerals are in a parallel alignment
Minerals are perpendicular to the force
Nonaffiliated
Contain equidimensional crystals
Resembles a coarse igneous rock
CLASSIFICATION
Based on texture Two groupsFoliated rocks
Nonfoliated
Foliated
Rocks
Slate
Fine - grained
Splits easily
Schist
Strongly foliated
" Platy "
Types based on composition
(e.g., mica schist)
Gneiss
Strong segregation of silicate minerals
" Banded " texture
Nonfoliated rocks
Marble
Parent rock - limestone
Calcite crystals
Used as a building stone
Variety of colors
Quartzite
Parent rock - quartz sandstone
Quartz grains are fused
Resources from rocks and minerals
Metallic mineral resources
e.g., Gold, silver, copper
Produced by
Igneous processes
Metamorphic processes
Resources from rocks and minerals
Hydrothermal (hot-water) solutions
Hot
Contain metal - rich fluids
Associated with cooling magma bodies
Types
Vein deposits occur in fractures or bedding planes
Disseminated deposits are distributed throughout the rock
Nonmetallic mineral
resources
Make use of the materials
Nonmetallic elements
Physical or chemical properties
Two broad groups
Building materials (e.g., limestone, gypsum)
Industrial minerals ( e.g., fluorite, corundum, sylvite)
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