Download interior structure of the earth

MR. SURRETTE
VAN NUYS HIGH SCHOOL
CHAPTER 1: ROCKS AND MINERALS
CLASS NOTES
INTRODUCTION TO ROCKS
There are three types of rocks: igneous, sedimentary, and metamorphic. Igneous rocks are formed by
the cooling and crystallization of hot, molten rock material called magma. Sedimentary rocks are
formed from weathered material (sediments) that are carried by water, wind, or ice.
INTRODUCTION TO ROCKS
Metamorphic rocks are formed from preexisting rocks that are transformed by high temperature or
pressure without melting.
MINERALS
Minerals are the building blocks of rocks. A mineral is a naturally formed, generally inorganic,
crystalline solid. Minerals are composed of an ordered array of atoms and have a specific chemical
composition.
CRYSTAL FORM
The orderly arrangement of atoms in a crystal is expressed in its shape, or crystal form. Every mineral
has its own crystal form.
POLYMORPHS
Two or more minerals that contain the same elements but have different structures are called
polymorphs. For example, the polymorphs graphite and diamond are both composed of pure
carbon.
CARBON POLYMORPHS
MINERAL HARDNESS
The resistance of a mineral to being scratched or its ability to scratch other minerals is a measure of
hardness.
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MOH’S SCALE OF HARDNESS
CLEAVAGE AND LUSTER
Cleavage is the tendency of a mineral to break along planes of weakness. Planes of weakness are
determined by crystal structure and chemical bond strength. The luster of a mineral is its ability to
reflect light.
COLOR AND STREAK
Although color is an obvious feature of a mineral, it is not very reliable. For example, the common
mineral quartz (SiO2), can be found in a variety of colors, depending on slight impurities. Streak, the
name given to the color of a mineral in its powdered form, is a better indicator.
DENSITY
Density is how heavy an object feels for its size. It can be determined using the equation:
=m/V
(Density = mass / volume)
Example 1. What is the density of silver if 26.25 grams occupies 2.5 cm3 volume?
1A.
(1)  = m / V
(2)  = 26.25 g / 2.5 cm3
(3)  = 10.5 g/cm3
SPECIFIC GRAVITY
The standard measure of density is specific gravity. Specific gravity is the ratio of a substance to an
equal volume of water. The density of water is 1 g/cm3:
Specific Gravity =  / (1 g/cm3)
Example 2. 6 cm3 of a mineral weighs 3 grams. What is its specific gravity?
2A.
(1)  = 6 cm3 / 3 grams
(2)  = 2 cm3 / gram
(3) Specific gravity =  / (1 g/cm3)
(4) Specific gravity = 2g/cm3 / 1g/cm3
(5) Specific gravity = 2
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ELEMENTS AND MINERALS
Of all the elements in the periodic table, 88 occur naturally in the Earth’s crust. These 88 elements
combine to make over 3,400 minerals. Almost half the mass found in minerals consists of oxygen. The
second most abundant element found in minerals is silicon.
THE SILICATES
Oxygen and silicon combine to form the most common mineral group, the silicates. The silicate
quartz, the second most common mineral, is composed entirely of oxygen and silicon.
THE OXIDES
Within the oxide minerals, oxygen combines with one or more metals. Oxides commonly contain the
metals iron, chromium, manganese, tin, and uranium.
THE CARBONATES
All carbonates contain the carbonate ion (CO32-). Two common carbonate minerals are calcite and
dolomite. Calcite and dolomite are the chief minerals that make up the limestone rocks.
THE SULFIDES AND SULFATES
The sulfide and sulfate minerals contain sulfur. Sulfides include the majority of ore minerals. The most
common sulfide is pyrite (fool’s gold), FeS2. In sulfates, sulfur is present as the sulfate ion (SO42-).
IGNEOUS ROCKS
95% of the earth’s crust is composed of igneous rock. On the continents, the most common igneous
rocks are granite and andesite. On the ocean floor, basalt is predominant. All igneous rock originates
as magma.
MAGMA
Magma is a mixture of liquid, melted rock, and dissolved gases. The most abundant chemical elements
in magma are silicon and oxygen. The oxide SiO2, silica, is the most abundant oxide in magma.
VISCOSITY
The term viscosity describes a fluid’s resistance to flow, or its internal friction. Lava becomes more
viscous as it cools. The amount of silica in lava also affects viscosity. Lava that is low in silica is less
viscous.
FRACTIONAL CRYSTALLIZATION
Igneous rocks form from the cooling and crystallization of magma. Crystallization is very similar to
melting, but in the reverse order: solid crystals form out of a liquid mixture. Minerals with high
melting points crystallize first, followed by minerals with low melting points. This process is called
fractional crystallization.
SHIELD VOLCANOES
When low-silica magma erupts, lava tends to flow freely and far. If it erupts from a single opening
(vent) or closely spaced vents, it forms a broad shield volcano.
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SHIELD VOLCANO
CINDER CONES
Cinder cones, such as Sunset Crater, generally have smooth steep slopes of 25o to 40o and bowl-shaped
summit craters.
CINDER CONE
COMPOSITE CONES
A composite cone forms by many eruptions of material with medium or high silica content. They erupt
violently when pressure builds up in the magma. Composite volcanoes are tall and have steep slopes
because lava does not flow easily.
COMPOSITE CONE
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INTRUSIVE AND EXTRUSIVE IGNEOUS ROCKS
Igneous rocks crystallize from cooling magma and lavas. Intrusive igneous rocks have cooled slowly
beneath the Earth’s surface. They are made of large crystals. Extrusive igneous rocks form from
magma brought to the Earth’s surface. These rocks cool rapidly and contain small crystals.
SEDIMENTARY ROCKS
Sedimentary rocks provide information about geological events that occurred at the Earth’s surface.
The most abundant sedimentary rocks are shale, composed of very fine particles, and sandstone,
composed of medium sized particles.
SEDIMENTATION
Weathering breaks down and decomposes surface rock. There are two kinds of weathering: mechanical
and chemical. Both types of weathering produce sediment. Mechanical weathering physically breaks
rocks into smaller and smaller pieces. Chemical weathering, which involves reactions with water, also
decomposes rock into smaller pieces.
EROSION
As rock is weathered, it erodes. Erosion is the process by which weathered rock particles are removed
and transported away by water, wind, or ice.
FOSSILS
Because sedimentary rocks are formed at the Earth’s surface, they often contain fossils, the remains of
preexisting life forms.
METAMORPHIC ROCKS
Igneous or sedimentary rocks may undergo change (metamorphism) if they are heated and/or
compressed for long periods of time. For example, shale subject to enough heat and pressure becomes
slate. It is important to note that no minerals are melted during metamorphism. Change occurs by the
recrystallization of preexisting minerals and the mechanical deformation of rock.
METAMORPHISM
Recrystallization often occurs when rocks subjected to high temperatures and pressures go through a
change in mineral assemblage. Rocks often lose water (H2O) or carbon dioxide (CO2) during this
process. Mechanical deformation occurs when a rock is subjected to physical stress.
TYPES OF METAMORPHISM
Metamorphism can be dynamic, contact, or regional.
DYNAMIC METAMORPHISM
Dynamic metamorphism involves mechanical deformation; for example, the shearing and grinding that
takes place in a fault zone.
CONTACT METAMORPHISM
Contact metamorphism occurs when a body of rock is intruded by magma.
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CONTACT METAMORPHISM
REGIONAL METAMORPHISM
Regional metamorphism is the widescale alteration of rock. This is found in all the major mountain
belts of the world.
THE ROCK CYCLE
Igneous, sedimentary, and metamorphic rocks have different origins. Although formed by different
processes, the three rock types are related, as seen in the rock cycle.
THE ROCK CYCLE
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