Earth Science Fall 2013
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Batholith- intrusive formation with at least a
surface exposure of 100 square kilometers
and reaching a depth of thousands of
meters
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Breccia- elastic sedimentary rock composed
of angular fragments
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Cementation- process in which dissolved
minerals left by water passing through
sediments bind sediments together
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Chemical sedimentary rock- rock formed
from minerals that precipitate out of water
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Clastic sedimentary rock- rock made up of
fragments from pre-existing rocks
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Compaction- process in which air and water
are squeezed out of sediments, resulting in
the formation of sedimentary rock
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Concretion- nodule of rock with a different
composition from that of the main rock body
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Conglomerate- sedimentary rock composed
of rounded gravel or pebbles cemented
together by minerals
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Contact metamorphism- change in the
structure and mineral composition of rock
surrounding an igneous intrusion
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Dike- igneous intrusion that cuts across rock
layers
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Evaporites- sedimentary rocks formed from
minerals left after water evaporates
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Extrusive igneous rock- rock formed from
molten lava that hardens on the earth’s
surface
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Foliated- describing metamorphic rock with
parallel bands
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Fossil- trace or remains of a plant or an
animal in sedimentary rock
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Igneous rocks- rock formed from cooled and
hardened magma
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Intrusive igneous rock- rocks formed from
the cooling of magma beneath the earth’s
surface
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Laccolith- flat-bottomed intrusion that
pushes overlying rock layers into an arc
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Lava Plateau- raised flat-topped area made
of layers of hardened lava
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Metamorphic rock- rock formed from other
rocks as a result of intense heat, pressure,
and chemical processes
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Metamorphism- changing of one type of rock
to another by heat, pressure, and chemical
processes
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Nonfoliated- describing a metamorphic rock
without parallel bands
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Organic sedimentary rock- rock formed from
the remains of organisms
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Porphyritic- describing an igneous rock
composed of both large and small crystals
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Regional metamorphism- metamorphism
that affects rocks over large areas during
period of tectonic activity
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Rock cycle- series of processes in which rock
changes from one type to another
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Sediment- fragments that result from the
breaking of rocks, minerals, and organic
matter
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Sedimentary rock- rock formed from
hardened deposits of sediment
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Sill- sheet of hardened magma that forms
between and parallel to layers of rock
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Stock- igneous intrusion with an area less
than 100 square kilometers
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Stratification- layering of sedimentary rock
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Volcanic neck- solidified central vent of a
volcano
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Magma from the earth’s interior is the
parent material for all rocks
From the time magma cools & hardens at or
near the surface of the earth, the resulting
rock begins to change.
Geologists have classified rocks into 3 major
types based on the way the rocks are
formed.
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3 major rock types
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Igneous rock
Sedimentary rock
Metamorphic rock
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2 groups of igneous rocks that are classified
according to where molten rock cools and
hardens
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Intrusive igneous rocks
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Magma cools below the crust
Extrusive igneous rocks
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Rapid cooling of lava on the earths surface
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Extrusive & intrusive igneous rocks differ
mainly in their sized of crystalline grain and
is known as texture
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Texture is determine by the cooling rate of the
magma or lava that formed the rock
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Slow loss of heat allows minerals to form
large, well-developed crystalline grains
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Coarse-grained texture
Ex: granite
Rapid loss of heat does not allow time for
large crystalline grains to form, this produces
fine-grained rock
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Ex: basalt
Oceanic crust is made mostly of basalt
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Lava or magma cools slowly at first & then
rapidly as it near the earth’s surface,
relatively large crystals embedded within a
mass of smaller ones
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Porphyritic
Highly viscous, silica-rich magma cools
rapidly and no crystals form
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Ex: obsidian
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Magma that contains large amounts of
dissolved gases hardens, the gases become
trapped in the rock and produces rock full of
holes
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Ex: pumice
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Determined by the chemical composition of
the magma from which the rock develops
Divided into 3 families
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Felsic
Intermediate
Mafic
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Felsic rocks
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Formed from magmas that are high in silica
Have light coloring of their main mineral
components, orthoclase feldspar & quartz
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May also contain plagioclase feldspar, biotite mica, &
muscovite mica
Ex: granite , rhyolite, obsidian
Obsidian may be black, blue, or red depending
on its chemical composition
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Mafic rocks
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Form from magmas that are low in silica but rich
in iron and magnesium
Also can include ferromagnesian minerals
making them dark in color
Ex: basalt , gabbro
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Intermediate Rocks
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Medium colored
Contain minerals such as plagioclase feldspar,
hornblende, pyroxene minerals, biotite mica
Contain less quartz than the felsic family
Ex: diorite , andesite
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Intrusions
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Largest of all intrusions are batholiths
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Form cores of several major mountain ranges like the
Sierra Nevada range in CA & the Coast Range in BC
A stock is similar to a batholith only much smaller
Laccoliths form when magma flows between rock
layers and spread upward sometimes pushing the
overlying rock into an arc
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Frequently found in groups
Ex: Black Hills
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Sills form when a sheet of magma flows
between layers of rock and hardens, it does not
cause the arcing like a laccolith
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Lie parallel to rock layers & vary in thickness from a
few cm to hundreds of meters
Ex: Big Bend National Park in Texas
When magma forces its way through rock layers
by following existing vertical fractures or by
creating new ones and solidifies is called a dike
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Common in areas of volcanic activity
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Extrusions
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A volcano is a cone of extrusive rock surrounding
a central vent, when a volcano stops erupting for
a long period the cone gradually wears away and
the solidified central vent is left, this is called a
volcanic neck
A lava plateau develops from lava that flows out
of long cracks in the earth’s surface
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Sedimentary rock is made up of
accumulations of various types of sediments
Compaction & cementation are 2 processes
that form sedimentary rocks
Sedimentary rocks are classified according
to the kind & size of sediments that form
them
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Clastic sedimentary rock is made up of rock
fragments carried away from their source by
water, wind, or ice & left as deposits
elsewhere
Chemical sedimentary rock forms from
minerals that precipitate from water
Organic sedimentary rock forms from the
remains of organisms
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Classified by the size of the sediments they
contain
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Conglomerate- rock composed of rounded gravel
sized fragments or pebbles
Breccia- rock made of rock fragments that are
angular & have sharp corners
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In both conglomerate and breccia the fragments can
be easily viewed
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Sandstones- rocks that are made up of sand
sized grains that have been cemented together
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Quartz is the major component
Many have pores between the sand grains through
which liquids can move
Shale- rock that consists of clay-sized particles
cemented and compacted under pressure
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Usually pressed into flat layers that will easily split
apart
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Form from dissolved minerals that were once
dissolved in water
Evaporites- rocks formed from the dissolved
minerals left behind from water evaporating
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Ex: gypsum & halite
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Bonneville Salt Flats, Utah
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Rocks formed from the remains of living things
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Ex: coal & some limestones
Coal forms from decayed plant remains that are
buried and compacted into matter that is
mostly carbon
Organic limestones- from marine animal shells
Chalk- made up of tiny, one-celled marine
organisms
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Originally forms as mud on the ocean floor
Ex: white cliffs of Dover, England
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Stratification
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Layering of sedimentary rock that occurs when
there is a change in the kind of sediment being
deposited
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Type of deposit varies for many reasons
Layers vary in thickness
Grade bedding- occurs when various sizes and
kinds of materials are deposited within one layer
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Ripple Marks & Mud Cracks
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Ripple marks are formed by the action of wind or
water on sand
Mud cracks result when muddy deposits dry and
shrink; the shrinking causes the dried mud to
crack
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Fossils
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Remains or traces of ancient plants and animals
Usually preserved in sedimentary rock
Concretions
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Lumps of rock with a different composition from the
main rock body
Form when minerals precipitated from solutions
build up around an existing rock particle
Groundwater sometimes deposits dissolved quartz
or calcite inside cavities of sedimentary rock where
it crystallizes and forms a geode.
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Metamorphism is the changing of one type
of rock to another by heat, pressure, and
chemical process
Most forms deep beneath the surface of the
Earth
All is formed from existing igneous,
sedimentary, or metamorphic rock
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During metamorphism certain minerals
change into other minerals; some minerals
change in size or shape or separate into
parallel bands that give the rock a layered
appearance
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2 types of metamorphism occur in the earth’s
crust
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Contact metamorphism occurs when rocks come
into direct contact with or very near magma
Regional metamorphism occurs due to heat and
pressure created by tectonic activity
Most metamorphic rock is formed by regional
metamorphism, however rocks formed by
contact metamorphism can also be found
where regional metamorphism has occurred.
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Classified according to their texture into two
categories
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Foliated- have parallel bands of minerals
Non-foliated- do not have parallel bands of
minerals
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Foliated Rocks
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Form in 2 ways
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Extreme pressure may flatten the mineral crystals in the
original rock & push them into parallel bands
Minerals of different densities separate into bands,
producing a series of alternating dark and light
Ex: slate, schist, gneiss
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Slate- formed by pressure acting on shale
Schist- formed when a greater amount of heat & pressure
change slate into a coarser-grained rock
Gneiss- greatly metamorphosed rock with bands of light
and dark minerals
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Do not have bands of crystals
Quartzite- forms when sandstone undergoes
metamorphosis
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Heat & pressure cause the mineral grains to
recrystallize so that the spaces between them
disappear
Marble- formed from the compression of
limestone