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Bellringer # 32
• Read “What are rocks good for?” page 755
• Answer both questions in your journal.
Chapter 21 S.3 Minerals
• A mineral is a naturally occurring inorganic
solid with an orderly crystalline structure and a
definite chemical composition.
Quartz
Mineral Characteristics
• 1. Naturally occurring- a mineral forms by
natural geologic processes.
• 2. Solid substance- minerals are solids within
the temperature ranges that are normal for
Earth’s surface.
• 3. Orderly crystalline structure- their atoms or ions
are arranged in an orderly and repetitive manner.
– All minerals are made of crystals.
– Some crystals can be very large (quartz) or very small
(sulfur).
– Quartz has an orderly structure. = mineral
– Opal does not have an orderly structure. = mineraloid
• 4. Definite chemical composition- most
minerals are chemical compounds that are
made of two or more elements.
– Quartz- 2 oxygen atoms for every silicon atom.
(SiO2)
– Gold and silver are made of only one element.
• 5. Inorganic- to be inorganic, a material must
not contain organic matter (living material). If
a sample contains fossils, it is not considered a
mineral, it would be a rock.
How Minerals Form
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Minerals form nearly everywhere on Earth.
Silicates- deep in the Earth
Carbonates- warm, ocean waters
Clay minerals- at the Earth’s surface, exposed
to weathering.
• There are four major processes by which
minerals form:
1. Crystallization from Magma
• Magma is molten rock.
• When it cools elements
combine to form minerals.
• The first ones to crystallize
are those rich in iron,
calcium, and magnesium.
• The composition of the
magma changes as minerals
form.
• Minerals rich in sodium,
potassium, and aluminum
form second.
Ex:
Feldspar
Muscovite
Hornblende
Quartz
2. Precipitation
• The water on Earth
contains dissolved
substances.
• When the water evaporates
the substances can react to
form minerals.
• Changes of temperature
can cause dissolved
substances to do the same
thing.
• Minerals are left behind or
precipitate out of the water.
EX: Limestone Cave
Ex: Halite and Calcite
3. Pressure and Temperature
• Some minerals form when existing minerals
are subjected to changes in pressure and
temperature.
• Increased pressure = recrystallize.
– Atoms are rearranged to form more compact
minerals.
• Temperature changes cause minerals to be
unstable.
• New minerals form that are stable at the new
temperature.
4. Hydrothermal Solutions
• A mixture of hot water and dissolved
substances.
– 100 degrees C and 300 degrees C
• Chemical reactions form new minerals.
• When the cool minerals like quartz and pyrite
can form.
• Ex:
– Bornite
– Pyrite
Mineral Groups
• Over 3,800 minerals have been named.
• Several new ones are identified each year.
• Common minerals, together with thousands of
others that form on Earth, can be classified
into groups based on their composition.
• The silicates are the most common on Earth.
Silicates
• The two most abundant elements in the Earth’s
crust are Silicon and Oxygen.
• Si and O combine to form a structure called
the silicon-oxygen tetrahedron.
• The tetrahedron can form different kinds of
bonds to form different kinds of minerals.
• They form when magma cools and sometimes
at high temperatures and pressure.
• Ex: Olivine, augite, micas, quartz, feldspar.
Carbonates
• Second most common mineral
group.
• Minerals that contain the elements
carbon, oxygen, and one or more
other metallic elements.
• Calcite is the most common
CaCO3
• Dolomite has magnesium and
calcium
• Limestone and marble are rocks
that have carbonates.
Oxides
• Minerals that contain oxygen
and one or more other
elements which are usually
metals.
• Rutile- it’s titanium oxide
– Magma cools
• Corundum- aluminum oxide
– Temper and pressure changes
• Hematite- iron oxide.
– Exposed to water
Sulfates and Sulfides
• Minerals that contain the element
sulfur.
• Sulfates
– Anhydrite
– Gypsum
– Form when mineral rich waters
evaporate.
• Sulfides EX: galena (mined for
lead) , sphalerite, pyrite (fools gold)
– Form from thermal or hot water
solutions.
Halides
• Minerals that contain a
halogen ion plus one or
more other elements.
• Elements from Group 7A.
– Fluorine, chlorine
• EX: Halite (NaCl) table salt,
– Fluorite (CaF2) used for
making steel.
• Forms when salt water
evaporates
Native Elements
• A group of minerals that
exist in a pure form.
• EX: gold, silver, copper,
sulfur, carbon.
• Native forms of carbon
– Diamond, graphite
• Some form from
hydrothermal solutions
Homework
• Read “A Possible Link Between Volcanism
and Climate Change in the Geologic Past”
• Answer the questions.
• Due tomorrow.
Bellringer # 33
• How would you characterize a mineral?
• List as many characteristics as you can.
• EX: think about a diamond, different minerals
that we discussed yesterday (halite, quartz,
feldspar, copper) or a birthstone, how would
you characterize it.
Properties of Minerals
• Minerals occur in different colors and shapes.
• They also very in the way they reflect light and
break.
• Some minerals are very hard and some have an
odor.
• All of these characteristics can be used to
identify them.
Color
• One of the first things you may notice.
• Color is unique to some but not all minerals.
– Not useful in identifying many minerals.
• Small amounts of different elements can give
the same mineral different colors.
• EX: sapphire most of the time they are blue
but they can be every color except red. Some
are lab created.
Streak
• The color of a mineral in its powdered form.
• Rub a mineral across a streak plate.
• Streak color does not vary like the color of a
mineral.
• Streak is a good indicator.
• Metallic minerals- dense, dark streak.
Luster
• Used to describe how light is
reflected from the surface of a
mineral.
• Minerals that have an appearance
of metal are said to have a metallic
luster. (copper)
• Nonmetallic minerals can be
glassy (quartz), pearly, silky,
earthy.
• Diamond has a brilliant luster.
• Some have sub-metallic luster.
Crystal Form
• The visible expression of a
mineral’s internal
arrangement of atoms.
• If it formed slowly and
with a lot of space it will
have well formed faces sides, top and bottom.
• Crowding causes lots of
small crystals to be
formed.
– None of them shows its
form.
Cubic Crystals
Hardness
• One of the most useful
properties.
• A measure of the resistance
of a mineral to being
scratched.
• You can rub two minerals
together. One will scratch
the other.
• Mohs scale- consists of 10
minerals arranged from 10
(hardest) to 1 (softest.
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Fingernail- 2.5
Penny- 3.5
Glass- 5.5
Quartz- hardest of the
minerals 7
• Diamonds- can scratch
anything, hardest mineral on
Earth
• Gypsum (2) can be
scratched by your fingernail.
• Calcite (3) cannot be
scratched by your fingernail.
Cleavage
• Minerals atomic structure is based on bonds.
• Some bonds are weak.
• Cleavage is the tendency of a mineral to cleave,
or break, along a flat even surface.
• Micas- simplest type of cleavage.
• Weak bonds, form thin sheets
• Silicates- cleave between the silicon-oxygen
structure.
• Quartz- no clevage, fractures instead.
• Halite- 3 directions of clevage, 90 degree angles
• Calcite- 3 directions of clevage, 75 degree angles
Fracture
• Minerals that do not show
cleavage when broken are said
to fracture.
• Fracture is the uneven breakage
of a mineral.
• Quartz- smooth, curvy, glassy
fracture
– Called conchoidal fracture
• Asbestos breaks into splinters or
fibers
– Called irregular fracture
Density
• Density is a property of all matter that is the
ratio of any object’s mass to its volume.
• D = Mass/Volume
• Unit = grams per cubic centimeter (g/cm3)
• The density of a pure mineral is a constant
value.
• Density can be used to determine the purity or
identity of some minerals.
Distinctive Properties of Minerals
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Some minerals have other distinctive properties.
Talc- feels soapy
Graphite feels greasy
Metallic minerals (gold, silver, copper) are easily
shaped.
Magnetite can be magnetic
Transparent calcite- double refraction
Some streaks that contain sulfur smell like rotten
eggs.
Carbonate minerals (calcite) will fizz when it
comes in contact with hydrochloric acid.
Rocks
• A rock is a solid mass of mineral or mineral-like
matter that occurs naturally as part of out planet.
• All rocks are composed of minerals.
• There are more than 4,000 minerals in Earth’s
crust
• The three major rock types are:
– Igneous
– Sedimentary
– Metamorphic
The Rock Cycle
• Old rocks in the rock cycle form new rocks.
– The sequence of events in which rocks can be
weathered, melted, altered, and formed is
described by the rock cycle.
– Rock formation occurs very slowly, often over tens
of thousands to millions of years.
– Depending on the circumstances, any type of rock
can become any other type of rock.
Alternate Paths
• Processes driven by heat from the Earth’s
interior are responsible for forming both
igneous and metamorphic rocks.
• Weathering and the movement of weathered
materials are external processes powered by
energy from the sun.
• External processes produce sedimentary rocks.
Formation of Igneous Rocks
• Igneous rocks form when
magma or lava cools and
hardens.
• Igneous – Latin- ignismeans fire
• If lava cools on the surface
it is called basalt.
• Different kinds of igneous
rocks form when magma
and lava cool and harden.
Intrusive Igneous Rocks
• Rocks the form when
magma hardens beneath the
Earth’s surface are called
intrusive igneous rocks.
• They intrude into the
existing rocks.
• We only see them because
of erosion.
• Magma is less dense than
other rocks, that is why it
surfaces.
• EX: Granite
Extrusive Igneous Rocks
• When magma reaches the
Earth’s surface it is called
lava.
• Difference, the gases have
escaped from lava.
• When lava hardens, the
rocks that form are called
extrusive rocks.
• They are extruded onto the
surface.
• EX: Rhyolite
Classification of Igneous Rocks
• Texture and composition are two
characteristics used to classify igneous rocks.
• Texture- the appearance of an igneous rock
based on its size, shape, and arrangement of
crystals.
• Composition- based on the proportions of light
and dark minerals in the rock.
1. Coarse-Grained Texture
• The rate of cooling
affects the texture.
• Slow cooling allows
– Few centers of crystal
growth development
– Ions to move large
distances
• Slow cooling results in
the formation of large
crystals.
2. Fine-Grained Texture
• Cools quickly
• Ions loose motion and
quickly combine.
• Lots of tiny crystals
compete for ions.
• Rapid cooling of
magma or lava results
in rocks with small,
interconnected
mineral grains.
3. Glassy Texture
• EX: Obsidian, pumice
• Lava moves too fast for
ions to arrange
themselves into a network
of crystals. No crystals
• Made of randomly
distributes ions.
4. Porphyritic Texture
• Huge amounts of magma deep
in the Earth will take thousands
of years to harden.
• Minerals that crystallize from
the magma form at different
times.
• Phenocrysts- large crystals
surrounded by fine grained
minerals.
• Experienced different rates of
cooling.
• EX: Andesite
5. Granitic Composition
• Made almost entirely of
light-colored silicate
minerals. (quartz, feldspar)
• They also contain about
10 % dark silicate minerals.
(biotite, mica)
• Contain 70% silica
• Major rocks of the crust
• EX: Rhyolite- extrusive
6. Basaltic Composition
• Contains many dark
silicate minerals and
plagioclase feldspar.
• Rich in magnesium
and iron.
• Darker and denser than
granitic rocks.
• EX: Basalt, Gabbro
7. Other Compositional Groups
• Composition between granitic and basaltic =
andesitic composition.
• Named after volcanic rock andesite.
• 25% dark silicates
• Main mineral- plagioclase feldspar
• Ultramafic- composed almost entirely of dark
silicate minerals. EX: periotite.
• Periotite makes up most of the mantle.
Homework
• Read Asbestos: What Are the Risks?
• Answer the questions
• Due tomorrow
Sedimentary Rocks
• Sedimentary comes from the Latin word
sedimentum - “settling”
• sedimentary rock: a rock formed from
compressed or cemented layers of sediment
Formation of Sedimentary Rocks
• The remains of older rocks form sedimentary
rocks.
– All rock breaks down over thousands of years by a
process known as weathering.
– As pieces of broken down rock accumulate, they
can form another type of rock— sedimentary rock.
• weathering: the natural process by which
atmospheric and environmental agents, such as
wind, rain, and temperature changes,
disintegrate and decompose rocks
5 major processes involved in the
formation of sedimentary rocks
1.Weathering
2.Erosion
3.Deposition
4.Compaction
5.Cementation
Weathering
• Often the first step in the formation of
sedimentary rocks.
• Chemical weathering- takes place when the
minerals in rocks change into new substances.
• Physical forces break rock into smaller pieces.
Erosion
• Erosion- involved weathering and the removal
of rock.
• When an agent of erosion – water, wind, ice,
or gravity – loses energy, it drops the
sediments.
– This is called deposition.
• Sediments are deposited according to size.
– Largest to smallest
• Some sediments are so small that they are
carried great distances first.
Compaction (weight)
• After deposition, sediments become lithified- turned into
rock.
• Compaction is a process that squeezes, or compacts
sediments.
• Caused by weight of sediments.
• Most of the water is driven out
Cementation (glue)
• Cementation takes place when dissolved minerals
are deposited in the tiny spaces among the
sediments.
• You can see the cement in conglomerate but not
in other types.
• Conglomerate- made of round pebbles cemented
together. (top left)
• Sandstone- made of sand grains cemented
together. (top right)
Classification of Sedimentary Rocks
• Sedimentary rocks are named according to the
size of fragments that they contain.
• Two main groups classified by how they form.
• Clastic sedimentary rocks- made of weathered
bits of rocks and minerals.
• Chemical sedimentary rocks- forms when
dissolved minerals precipitate from water
solutions.
Clastic Sedimentary Rocks
• Most common minerals are clay and quartz.
– Clay- product of chemical weathering
– Quartz- durable, resistant to chemical weathering
• Grouped by the size of the sediments in the rock.
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Conglomerate- gravel size particles, well rounded
Breccia- angular particles
Sandstone- most sediments are sand sized grains
Shale- most common sedimentary rock
– Made of very fine grained sediment
• Siltstone- also fine grained
Conglomerate
Sandstone
Breccia
Shale
Siltstone
Chemical/Biochemical
Sedimentary Rocks
• Forms when dissolved minerals
precipitate from water solutions.
– Water evaporated or boils off leaving
a solid.
• Ex: limestones, rock salt, chert,
flint, and rock gypsum, chalk,
coquina
Features of some Sedimentary Rocks
• Features of these rocks are clues to how, when, and
where the rocks formed.
• Each layer records a period of sediment deposition.
• Ripple marks- formed along a beach or stream bed.
• Fossils- tell whether the rock formed on land or in
the ocean, climate, when it formed.
Metamorphic Rocks
• Rocks that undergo pressure and heating without
melting form metamorphic rock.
– Heat and pressure within Earth cause changes in the
texture and mineral content of rocks.
– The word metamorphic comes from the Greek word
metamorphosis, which means “to change form.”
• metamorphic rock: a rock that forms from other
rocks as a result of intense heat, pressure, or
chemical processes
Formation of Metamorphic Rocks
• Most changes occur at elevated temperatures
and pressures.
• Conditions like this can be found a few
kilometers below Earth’s surface and extend
into the upper mantle.
• There are two settings for metamorphism
1. Contact Metamorphism
• During contact
metamorphism, hot magma
moves into rock.
• Considered a low grade
metamorphism
• Ex: marble
• Marble often forms when
magma intrudes a
limestone body.
2. Regional Metamorphism
• Results in large scale deformation and high grade
metamorphism.
• Mountain building can cause the kind of extreme
pressure and temperature.
Agents of Metamorphism
There are three agents
1. Heat
2. Pressure
3. Hydrothermal solutions
•
Rocks usually experience all three at the same
time.
•
The effect of each is different.
Heat
• The most important agent.
• Provides energy for chemical reactions.
• Reactions
– Existing minerals recrystallize
– New minerals form
• Heat comes from magma and the change in
temperature with depth.
• 150-200 degrees C
– Silicates are stable
– Clay minerals recrystallize to form chlorite and
muscovite.
Pressure (Stress)
• Also increases with depth.
• Pressure on rocks within the Earth occur in all
directions.
• Causes the spaces between mineral grains to
close.
• Results in a more compact rock with greater
density.
• Increase in temperature and pressure cause rocks
to flow rather than fracture.
– Mineral grains tend to flatten and elongate
• Metamorphic rocks may be changed in two
ways.
1. by heat alone
2. by heat and pressure (more common)
– The most common types of metamorphic rocks
are formed by heat and pressure deep in the crust.
– Pressure causes folds in the rocks.
Classification of Metamorphic Rocks
• Metamorphic rocks are classified by texture
and composition.
• The texture is either
– Foliated- banded appearance
– Nonfoliated- contain only one mineral
Bellringer # 39
• 1. What is erosion?
• 2. How does wind cause erosion?
• 3. How does water cause erosion?
• 4. How does ice cause erosion?