Rocks: Materials of the Solid EarthChapter 3
Earth Science, 13e Stanley C. Hatfield, Southwestern Illinois College
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Objectives•What is the rock cycle and why is it
important?•What are the three groups of rocks and
the geologic processes involved in the formation of each?
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Objectives•How does magma differ from lava?•What two criteria are used to classify
igneous rocks?•How does the rate of cooling influence the
crystal size of minerals in igneous rocks?
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Objectives•What are the names and environments of
formation for some common detrital and chemical sedimentary rocks?
•What processes change sediment into sedimentary rock?
•What are two characteristics of sedimentary rock?
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Objectives•What are metamorphic rocks and how do
they form?•What are the agents of metamorphism?•What are the names, textures and
environments of formation for some common metamorphic rocks?
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The rock cycle6
Rock cycle •Shows the interrelationships among the
three rock types •Earth as a system: the rock cycle
▫Magma Crystallization
▫Igneous rock Weathering, transportation, and deposition
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Rock cycle •Earth as a system: the rock cycle
▫Sediment Lithification
▫Sedimentary rock Metamorphism
▫Metamorphic rock Melting
▫Magma
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Rock cycle •Earth as a system: the rock cycle
▫Full cycle does not always take place due to “shortcuts” or interruptions e.g., Sedimentary rock melts e.g., Igneous rock is metamorphosed e.g., Sedimentary rock is weathered e.g., Metamorphic rock weathers
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The rock cycle 10
Igneous rocks •Form 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
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Igneous rocks •Crystallization of magma
▫Ions are arranged into orderly patterns ▫Crystal size is determined by the rate of
cooling Slow rate forms large crystals Fast rate forms microscopic crystals Very fast rate forms glass
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Igneous rocks •Classification is based on the rock’s
texture and mineral constituents ▫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
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Igneous Rock Textures
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Glassy Texture
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Obsidian exhibits a glassy texture
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Fine-grained igneous texture17
Porphyritic igneous texture18
Course-grained igneous texture19
Igneous rocks •Classification is based on the rock’s
texture and mineral constituents ▫Mineral composition
Explained by Bowen’s reaction series which shows the order of mineral crystallization
Influenced by crystal settling in the magma
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Classification of igneous rocks21
Common Igneous Rocks22
Bowen’s reaction series23
Igneous rocks • Naming igneous rocks
▫Granitic rocks Composed almost entirely of light-colored silicates –
quartz and feldspar Also referred to as felsic: feldspar and silica (quartz) High silica content (about 70 percent) Common rock: granite, rhyolite
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Intrusive vs. Extrusive25
Igneous rocks •Naming igneous rocks
▫Andesitic rocks Midway between granitic and basaltic Mostly amphibole (dark) and plagioclase
feldspar (light) Also referred to as intermediate Common rock: diorite, andesite
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Intrusive vs. Extrusive27
Igneous rocks •Naming igneous rocks
▫Basaltic rocks Contain substantial dark silicate minerals
and calcium-rich plagioclase feldspar Also referred to as mafic: magnesium and ferrum (iron)
Common rock: gabbro, basalt
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Intrusive vs. Extrusive29
Igneous rocks •Naming igneous rocks
▫Ultramafic (dark) – olivine, pyroxene Rare at Earth’s surface but peridotite is
believed to be a primary constituent of Earth’s mantle.
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Bowen’s Reaction Series•N. L. Bowen (early 20th century)
discovered that magma crystallizes over a range of temperatures.
•Each rock group consists of minerals that crystallize in same temperature range.
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Bowen’s Reaction Series•Continuous :
▫When plagioclase is very hot it is calcium rich, when it cools it becomes sodium rich
▫Temperature-induced chemical reaction•Discontinuous:
▫At a certain temperature a magma might produce olivine, but if that same magma was allowed to cool further, the olivine would "react" with the residual magma, and change to the next mineral on the series.
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Sedimentary rocks •Form from sediment (weathered products)•About 75 percent of all rock outcrops on the
continents•Used to reconstruct much of Earth’s history
▫Clues to past environments ▫Provide information about sediment transport ▫Rocks often contain fossils
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Sedimentary rocks •Economic importance
▫Coal▫Petroleum and natural gas ▫Sources of iron and aluminum
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Sedimentary rocks •Classifying sedimentary rocks
▫Two groups based on the source of the material Detrital rocks
Material is solid particles Classified by particle size Common rocks include
▫Shale (most abundant) ▫Sandstone▫Conglomerate
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Classification of sedimentary rocks
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Conglomerate vs. breccia37
Sandstone vs. siltstone
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Shale with plant fossils39
Once a rock(er), now a fossil…
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Sedimentary rocks •Classifying sedimentary rocks
▫Particle size provides information about env’t in which sediment was deposited
Stronger currents (air, water, glaciers) carry larger particles
Sand – less energy Silts/clays settle slowly associated w/quiet
waters Can be a mix of particle sizes (ex: sandy
siltstone)▫Mineral composition
Ex: quartz sandstone
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Sedimentary rocks •Classifying sedimentary rocks
▫Two groups based on the source of the material Chemical rocks
Derived from material that was once in solution and precipitates to form sediment ▫Directly precipitated as the result of physical
processes, or ▫Through life processes (biochemical origin)
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Sedimentary rocks •Classifying sedimentary rocks
▫Two groups based on the source of the material Chemical rocks
Common sedimentary rocks ▫Limestone – the most abundant chemical rock ▫Microcrystalline quartz (precipitated quartz)
known as chert, flint, jasper, or agate ▫Evaporites such as rock salt or gypsum▫Coal
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Biochemical Sedimentary RockA.Coquina
B. Seashells @ Sanibel Island, Florida
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Biochemical Sedimentary RockWhite Chalk Cliffs,
Sussex England (chalk is soft, porous limestone)
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Inorganic Limestone•Chemical changes, high water temp
raise CaCO3 concentration to the point that it precipitates.
•Chert – dense, hard rocks made of microcrystalline quartz▫Agate – banded▫Flint – dark color comes from organic
matter▫Jasper – red due to iron oxide▫Arrowheads, etc. often made from chert
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Chert
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Evaporite Deposits•Halite, gypsum (used in drywall, plaster)•Salt flats form when water evaporates,
precipitates remain
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Coal Formation•No oxygen present to
allow for complete decay of plant material (stagnant swamp for example)
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Sedimentary rocks •Sedimentary rocks are produced through
lithification ▫Loose sediments are transformed into solid
rock ▫Lithification processes
Compaction Cementation by
Calcite Silica Iron Oxide
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Sedimentary rocks •Features of sedimentary rocks
▫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
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Sedimentary EnvironmentsRipple marks in sedimentary rock, indicative of a beach or stream channel
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Sedimentary Environments• Mud cracks form
when wet mud or clay dries & shrinks• Indicative a tidal
flat or desert basin
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Earth as a System•The Carbon Cycle and Sedimentary Rocks
p. 69
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Metamorphic rocks •“Changed form” rocks •Produced from preexisting parent rock
▫Igneous rocks▫Sedimentary rocks▫Other metamorphic rocks
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Metamorphic rocks •Metamorphism
▫Takes place where preexisting rock is subjected to temperatures and pressures unlike those in which it formed
▫Degrees of metamorphism Exhibited by rock texture, mineralogy
(composition) Low-grade (e.g., shale becomes slate) High-grade (obliteration of original features)
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Metamorphic rocks •Metamorphic settings
▫Contact, or thermal, metamorphism Occurs near a body of magma (intrusive
magma) Changes are driven by a rise in temperature
▫Regional metamorphism Directed pressures and high temperatures
during mountain building Produces the greatest volume of
metamorphic rock
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Metamorphic rocks •Metamorphic agents (often all 3 at once)•Heat, pressure, chemically active fluids
▫Heat Triggers chemical reactions that result in
recrystallization/formation of new minerals Intrusion of magma “bakes” the rock OR Temperature gradually rises as rocks are
carried deeper (~25C/km) @ 8 km (200C) clay becomes unstable, morphs
to chlorite and muscovite
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Chlorite, Muscovite
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Metamorphic rocks •Metamorphic agents (often all 3 at once)
▫Pressure (stress) From burial (confining pressure) From differential stress during mountain
building Result is more compact rock with greater
density▫At Earth’s surface (lower temp.), rocks are
less ductile and tend to fracture when stressed
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Origin of pressure in metamorphismA.Decrease in
volumeB.Shortening in
same direction as pressure, lengthening in perpendicular direction
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Metamorphic rocks •Metamorphic agents (often all 3 at once)
▫Chemically active fluids Mainly water and other volatiles
change to gas at Earth’s surface Promote recrystallization by enhancing ion
migration As temp increases, ions become more reactive
Hot fluids circulate freely through rocks Dissolve materials from regions of high stress and
deposit them in areas of low stress Minerals tend to recrystallize and grow longer in a
direction that is perpendicular to compressional stress
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Metamorphic rocks •Metamorphic textures
▫Pictures of Foliated and Non-Foliated Rock Types
• Foliated texture Minerals are in a parallel alignment Minerals are perpendicular to the
compressional force ▫Nonfoliated texture
Contain equidimensional crystals Resembles a coarse-grained igneous rock
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Development of foliation due to directed pressure
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Animation
Metamorphic rocks •Common metamorphic rocks
▫Foliated rocks Slate
Fine-grained Splits easily Can be different colors
Schist Strongly foliated “Platy” Types based on composition (e.g., mica schist) Name is based on texture rather than composition
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Classification of metamorphic rocks
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Metamorphic rocks •Common metamorphic rocks
▫Foliated rocks Gneiss
Strong segregation of silicate minerals “Banded” texture
▫Nonfoliated rocks Marble
Parent rock is limestone Large, interlocking calcite crystals
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Metamorphic rocks •Common metamorphic rocks
▫Nonfoliated rocks Marble
Used as a building stone Variety of colors
Quartzite Parent rock – quartz sandstone Quartz grains are fused
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Foliated Metamorphic Rock
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Foliated Metamorphic Rock71
Foliated Metamorphic Rock
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Nonfoliated Metamorphic Rock
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Nonfoliated Metamorphic Rock
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Resources from rocks and minerals •Metallic mineral resources
▫Gold, silver, copper, mercury, lead, etc. ▫Concentrations of desirable materials are
produced by Igneous processes Metamorphic processes
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Resources from rocks and minerals •Metallic mineral resources
▫Most important ore deposits are generated from hydrothermal (hot-water) solutions Hot Contain metal-rich fluids Associated with cooling magma bodies Types of deposits include
Vein deposits in fractures or bedding planes, and
Disseminated deposits which are distributed throughout the rock
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Resources from rocks and minerals •Nonmetallic mineral resources
▫Make use of the material’s 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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Nonmetallic mineral resources 78
End of Chapter 3
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