Download There are about 3000 different minerals in the Earth`s crust!

MINERALS
3 characteristics of minerals
1) Minerals are naturally occurring,
inorganic solids
2) Each has a specific chemical
composition
3) Each has a definite crystalline structure
Naturally Occurring Inorganic Solids
• Minerals are formed by natural processes
– Synthetics and substances developed in labs
are NOT minerals
• Inorganic means they are not alive and
have never been alive
– Sugar is not a mineral—it is harvested from
plants
– Coal is not a mineral—it is from decayed
living things
Why is a natural
emerald considered
to be a mineral, but a
synthetic emerald is
NOT considered to
be a mineral?
Synthetic is not
natural!
Why is halite (rock salt)
considered to be a
mineral, while rock
candy (crystallized
sugar) is NOT
considered to be a
mineral?
Sugar comes from a plant!
Rock salt was never alive!
Solids with a Specific Chemical Composition
• Minerals are not
liquids or gases
• Minerals are a
specific element
or compound
– The chemical
composition of
a specific
mineral is in a
well-defined
range
CRYSTAL
A solid in which the atoms are
arranged in repeating patterns
• Easy to see the crystal system if the
mineral is grown in an open space
and grows into one large crystal
– RARELY HAPPENS
• The crystal system may be not
obvious is the crystal grew in a
restricted space
– MORE COMMON
Why is a gypsum crystal
considered to be a
mineral, but a typical rock
you would pick up outside
would NOT be
considered to be a
mineral?
Gypsum has a definite
crystal structure, but a
rock does not!
Sources of
Minerals
1) Magma: molten material found beneath Earth’s
surface
– Density differences force magma upward into
cooler layers of Earth’s interior, where the
magma cools
– The compounds in the magma no longer move
freely and they begin to interact chemically to
form minerals
– Rate at which the magma cools determines the
size of the crystals
Sources of
Minerals
2) SOLUTION
Minerals precipitate
(or drop out of)
solutions that are
supersaturated (or
overfilled) or when
water evaporates
from a
supersaturated
solution.
•
•
•
•
Only 30 of the 3000
minerals in Earth’s crust
are common
The most common are
referred to as rockforming minerals
because they make up
most of the rocks found
in Earth’s crust.
About 90 known
elements occur naturally
in the Earth’s crust
The vast majority of
minerals are made up of
the 8 most common
elements.
MINERAL GROUPS
Silicates
Contain silicon and
oxygen and usually
one or more other
elements
•
96% of the
minerals in
Earth’s crust
•
Most common
minerals:
Feldspar &
Quartz
The bonds between the atoms determine
mineral splits
MINERAL GROUPS
Carbonates
Minerals composed of one or more metallic elements
with the carbonate compound (CO3)
•
Primary minerals in limestone and marble
•
Some have distinctive colorations
•
Examples: Calcite, dolomite, azurite, malachite
MINERAL GROUPS
Oxides
Compounds of oxygen and a metal
• Examples: Hematite, Magnetite (good sources of
iron) and Uraninite (source of uranium)
Other Mineral Groups
Sulfides, sulfates, halides, and native elements
MINERAL IDENTIFICATION
• There are 7 ways minerals can be identified
• It is best to use a combination of tests rather
than just one
• The 7 tests: Color, Luster, Texture, Streak,
Hardness, Cleavage & Fracture, Density &
Specific Gravity
COLOR
• Sometimes caused by trace elements or
compounds within a mineral
• One of the least reliable clues to a
mineral’s identity
LUSTER
• The way that a mineral reflects light from its
surface
• Described as either metallic or nonmetallic
– Metallic: Reflect light
• Gold, silver, copper, galena
– Nonmetallic: Dull, pearly, waxy or silky
• Calcite, gypsum, sulfur and quartz
• Differences in luster are caused by differences in
the chemical compositions of the minerals
TEXTURE
• How a mineral feels to the touch
– Smooth, rough, ragged, greasy, soapy or
glassy
STREAK
• The color of a mineral when it is broken up and
powdered
– A colored powdered streak is left behind by some
minerals when they are rubbed across an unglazed
porcelain plate
– Sometimes does not match the mineral’s external
color
• Pyrite (fool’s gold) leaves a greenish-black streak, while real
gold leaves a yellow streak
– A mineral’s streak rarely changes
– Can only be used on minerals softer than a porcelain
plate
• Cannot be used to identify all minerals
HARDNESS
• Measure of how easily a mineral can be
scratched
• Mohs scale: Developed by the German geologist
Friedrich Mohs
– Scale in which an unknown mineral’s hardness can
be compared to the known hardnesses of 10 minerals
– Any mineral with a greater hardness than another
mineral will scratch the softer mineral
• One of the most reliable tests
Moh’s Scale
Hardness Examples:
1) A mineral that can
scratch quartz would
have a hardness >
__________.
2) A mineral you could
scratch with your
fingernail would have a
hardness <
___________.
3) Would Talc be able to
scratch quartz? Why or
why not?
CLEAVAGE AND FRACTURE
• A mineral that splits relatively easily and evenly
along one or more flat planes has cleavage
– Minerals that break into sheets have weak atomic
bonds
• A mineral that breaks with rough or jagged
edges are said to have fracture
– Minerals that break unevenly or along jagged edges
have tightly bonded atoms
– Conchoidal fracture: Fracture with arclike patterns
resembling clam shells (flint, chalcedony, obsidian)
CLEAVAGE VS. FRACTURE
DENSITY & SPECIFIC GRAVITY
• Density: mass per unit volume (D = m/V)
– Pyrite = 5.2 g/cm3; Gold = 19.0 g/cm3
– Reflects the atomic weight and structure of a
mineral
• Specific Gravity: The ratio of the weight
of a substance to the weight of an equal
volume of water at 4C (39.2F)
– Most common measure of density used by
geologists
SPECIAL PROPERTIES
• Double refraction: The refraction of a
single ray of light into two rays creating
two images
•Calcite also fizzes when it comes in contact with
hydrochloric acid
•Magnetite: Naturally magnetic
•Sphalerite: Distinctive rotten egg odor when rubbed
on streak plate (sulfide)
MINERAL USES
• Minerals are virtually everywhere
• Computers, cars, tv’s, desks, roads,
buildings, jewelry, beds, paints, sports
equipment, medicines, etc.
ORES
• A mineral is an ORE if it contains a useful
substance that can be mined at a profit
– Hematite: Ore that contains IRON
– Bauxite: Ore that contains ALUMINUM
MINES
• Ores that are located deep within the Earth’s
crust are removed by underground mining
• Ores that are near Earth’s surface are obtained
from large, open-pit mines
– Waste material must be separated from the ore
before the ore can be used
• If the cost of removing the waste is higher than the value of
the ore then the mineral will no longer be classified as an ore
and it is not economical to mine it
– Classification of a mineral as an ore may if the supply
of or demand for that mineral changes.
• If demand drops substantially, the mineral is no longer
considered an ore
GEMS
• Valuable minerals that are prized for their
rarity and beauty
– The more rare, the more valuable
– Trace elements can make one variety of a
mineral more colorful and thus more prized
than other varieties of the same mineral