Transcript Minerals and Rocks - Westmoreland Central School

Earth Science
Chapter 3
Minerals and Rocks
Minerals
• A mineral is a naturally occurring, solid,
inorganic substance that has a definite
chemical composition and molecular
structure.
– Naturally occurring means not made artificially
– Inorganic means it is not now, nor ever has
been alive.
• Minerals are classified on the basis of
their physical and chemical properties.
Mineral Characteristics
• The physical properties of a mineral are
due largely to the internal arrangement of
atoms.
• The six key physical properties that can be
seen or easily tested are: color, streak,
luster, hardness, and cleavage or fracture.
Mineral Characteristics
• Color
– Most visible property
– Color alone is not a good mineral identifier.
• Many minerals exhibit the same color.
• Many minerals are found in a variety of colors.
Mineral Characteristics
• Streak
– The color of a mineral in its powdered form.
– Streak is reliable for mineral identification.
• Streak may be different from mineral color.
Mineral Characteristics
• Luster
– The way in which light is reflected from the
surface of a mineral.
– Minerals with metallic luster shine like
polished metals.
– Minerals with nonmetallic luster have no
metallic shine.
• Nonmetallic lusters can be glassy, dull,
earthy, etc.
Mineral Characteristics
• Metallic lusters
• Nonmetallic lusters
Mineral Characteristics
• Hardness
– A mineral’s resistance to being scratched
– The relative hardness of a mineral is
determined by comparing it to the hardness of
ten “standard” minerals that make up Moh’s
Hardness Scale.
– Minerals are often compared to the hardness
of glass (5.5).
Mineral Characteristics
• Cleavage
– The tendency of a mineral to split along one
or more smooth surfaces or planes.
Mica (1 plane)
Halite (3 planes)
Mineral Characteristics
• Fracture
– Minerals that don’t show cleavage, fracture
unevenly when they break.
Mineral Characteristics
• Other properties
Magnetic
Salty Taste
React with Acid
Bad Odor
Formation of Minerals
• All minerals are crystalline, or made up of
atoms arranged in a pattern.
• Minerals are grouped according to their
chemical composition.
– All minerals are made up of elements.
– Minerals are classified based upon the
elements they contain.
– Most common minerals in the crust are
silicates (made of silicon and oxygen).
Formation of Minerals
– Of all the minerals on the Earth’s crust, over
90% are a combination of the following eight
elements:
Percent By Mass in Crust
Oxygen 46.4 %
Silicon 28.2%
Aluminum 8.2%
Iron 5.6 %
Calcium 4.2%
Sodium 2.4%
Magnesium 2.3%
Potassium 2.1%
Others 0.6%
Rocks
• Most rocks are composed of one or more
minerals.
– Rocks composed of one mineral are called
monominerallic.
– Rocks composed of more than one mineral
are called polyminerallic.
• Most rocks have a number of minerals in
common.
– Of the over 2,500 different minerals, only 10
to 15 minerals compose 90% of rocks.
Rocks
• Differences between rocks and minerals
– Minerals have a uniform composition while
the physical properties of rocks vary from one
rock to the next.
– Minerals are classified by physical properties
while rocks are classified by their origin.
• Igneous - solidification of molten rock
• Sedimentary - compaction and cementation
of sediments
• Metamorphic - recrystalization of rock
Igneous Rocks
• Igneous rocks form as a result of the
solidification of molten rock material.
– Molten rock beneath the Earth’s surface is
called magma.
– Molten rock that reaches the Earth’s surface
is called lava.
• When molten rock solidifies, it crystallizes
into igneous rock.
Igneous Rocks
• The texture, or grain appearance, depends
on the size and arrangement of crystals.
– Intrusive igneous rocks:
• Form from magma underground
• Solidify slow & have large crystals
– Extrusive igneous rocks:
• Form from lava above ground
• Solidify quick & have small crystals
Igneous Rocks
• Igneous rocks are grouped according to
their mineral composition.
– Felsic igneous rocks
• Light color
• Low density
• Most common on continents
– Mafic igneous rocks
• Dark color
• High density
• Most common on ocean floor
Sedimentary Rocks
• Sedimentary rocks form as a result of
compaction and cementation of
sediments.
– Sediments are changed into rock after they
are transported and deposited.
– Most sedimentary rocks are deposited in large
bodies of water.
– The presence of sedimentary rocks suggests
area was underwater at time of formation.
Sedimentary Rocks
• Compaction
– Pressure created by water and overlying
sediments can force particles of sediment close
together and compress them into rock.
• Cementation
– The addition of minerals, such as silica, lime, or
iron oxide, tends to glue rock particles together
to form solid rock.
Sedimentary Rocks
• Clastic Sedimentary Rock
– Formed from sediments made up of rock
fragments held together by cement
– Layers or cementing material are often visible
Sedimentary Rocks
• Chemical or Crystalline Sedimentary Rocks
– Form as a result of chemical processes
• Water with dissolved minerals evaporates
• Minerals that precipitate out forms crystals
Rock Salt
Rock Gypsum
Sedimentary Rocks
•
Bioclastic or Organic Sedimentary Rocks
– Form from remains of dead organisms.
• Coal forms as a result of compression of
plant remains.
• Limestone can be made of shells.
Coal
Limestone
Metamorphic Rocks
• Metamorphic rocks form as a result of
recrystallization of unmelted material
under conditions of high temperature and
pressure over long periods of time.
– Recrystallization is a process in which rocks
undergo change without true melting.
– As a result of heat and pressure minerals in
the rocks combine to form new, larger, denser
crystalline structures.
Metamorphic Rocks
• Banding and foliation of minerals are the
most outstanding characteristic of
metamorphic rocks.
– Due to concentrations of various minerals into
zones of different colors
– Not to be confused with layering of
sedimentary rocks
Metamorphic Rocks
• Types of Metamorphism
– Contact metamorphism
• Molten rock comes in contact with nearby rock
• Heat from magma alters the rock it touches
– Regional metamorphism
• Large areas of rock are under intense heat
and pressure
• Generally associated with mountain building
The Rock Cycle
• The rock cycle describes how rocks of all
types can be changed into other rocks.
– Earliest rocks formed on Earth were igneous
– They were uplifted, weathered, and eroded to
form sediments.
– The sediments were deposited, buried and
compacted into sedimentary rocks.
– Sedimentary and igneous rocks were subject to
heat and pressure to form metamorphic rocks.
Mineral Conservation
• Today the world’s need for energy
resources is greater than ever.
– Most energy sources-coal, oil, and natural
gas-are nonrenewable (used faster than they
can be replaced).
– Coal oil and natural gas are called fossil fuels
because they are made of the remains of
plants and animals that lived long ago.
– Fossil fuels and other nonrenewable
resources are vital to our everyday lives.
Mineral Conservation
– Alternate sources of renewable energy
resources are under development.
• Water power
• Wind power
• Solar energy
• Geothermal energy
– The use and distribution of mineral resources
have global, financial and political implications.
– THEY MUST BE USED WISELY.