Download Rocks and minerals Solid Earth materials Minerals Crystal structures

Solid Earth materials
Rocks and minerals
Chapter 17
Minerals
• Earth science definition: a naturally occurring,
inorganic solid element or compound with a
crystalline structure
– Cannot be synthetic
– Not directly produced by a living organism
– Must have regular, repeating pattern
• Example: halite (NaCl)
• Nonuniform distribution of
matter
• Molten core
– Contains most heavy
elements
– Iron, nickel
• Thin surface crust
– Mostly lighter elements
– 8 elements make up 98.6%
of crust
– Rocks and minerals make up
solid crust materials
Crystal structures
• Can be made up of one
or more kinds of element
– Diamond - carbon only
– Quartz - silicon and
oxygen
• Classification
– Based on surface
symmetries
– Six major systems:
isometric, hexagonal,
tetragonal, orthorhombic,
monoclinic and triclinic
Silicates and nonsilicates
Silicates
•
•
•
•
Contain mostly silicon and oxygen
Make up 92% of Earth’s crust
Based on silicon-oxygen tetrahedral
unit
Four major arrangements
1.
2.
3.
4.
Nonsilicates
• No silicon-oxygen
tetrahedrons in
crystalline structure
• Make up remaining
8% of Earth’s crust
• Eight groups of
nonsilicates
1. Carbonates
–
2.
3.
4.
5.
6.
7.
8.
Most abundant
Sulfates
Oxides
Sulfides
Halides
Phosphates
Hydroxides
Native elements
Isolated tetrahedrons
Chain silicates
Sheet silicates
Framework silicates
Physical properties of minerals
• Color
– Not very useful
– Can be influenced by trace
impurities
• Streak
– Color of the mineral when finely
powdered
– More consistent than color
• Hardness
– Resistance to scratching
– Mohs hardness scale
• Uses ten test minerals with
increasing hardness
More physical properties
• Crystal form
– Related to the internal
geometric arrangement of
atoms
– Six basic groups already
mentioned
• Cleavage
– Tendency of minerals to break
along smooth planes
• Fracture
– Irregularity in broken surfaces
• Luster
– Surface sheen
– Types include metallic, pearly
and vitreous
• Density
– Mass to volume ratio
– Alternative: specific gravity
(ratio of mineral density to that
of water)
– Two factors: kinds of atoms
making up the mineral; packing
of the atoms into the crystal
lattice
Minerals formed at high temperatures
• Bowen’s reaction series
– Silicate crystallization sequence
– Ferromagnetic silicates crystallize at higher temperatures
– Minerals crystallizing later are progressively richer in silicon
Mineral forming processes
Formation in two liquid
environments most common
1. Water solutions
–
Crystals form from highly
concentrated ions
2. Magma
–
–
–
Molten rock from which
minerals can crystallize
Can happen below or above
Earth’s surface
Lava: magma forced out to the
Earth’s surface
• Important factors
–
–
–
–
Temperature
Pressure
Time
Availability and
concentration of ions in
solution
• Glass
– Rapidly cooled solid
lacking a crystalline
structure
Minerals formed at normal
temperatures
• Formed at the Earth’s surface in contact with
oxygen, carbon dioxide and water
• Carbonates, sulfates, oxides, halides and sulfides
• Except for oxides, have substantially lower
hardnesses and specific gravities than minerals
formed at high temperatures
Altered minerals
• Exposure to different environmental pressure,
temperature or chemical solutions can change
minerals into new ones
• Generally occurs above 150ºC and 2000
atmospheres of pressure
• Examples: garnet, epidote, talc, graphite and
serpentine (asbestos source)
Rocks
• Aggregation of one or
more minerals and
perhaps other
materials
• Minerals are
physically combined to
make rocks
• Most rocks are silicate
minerals
•
Ore minerals
•
•
•
•
Mineral deposits with economic value
Often found in veins
Thin, flat bodies of mineral material
Left over from crystallizing magma and flushed
away in hot water solutions
• Examples: pyrite (iron sulfide,“fool’s gold”),
calcopyrite (sulfide of copper and iron)
Igneous rocks
Classification
scheme
– Based on how rocks
were formed
– Three main groups
1. Igneous
2. Sedimentary
3. Metamorphic
• Formed from magma
above or below Earth’s
surface
• All rocks were at one time
igneous rocks
• Cooling rate determines
the texture
• Intrusive igneous rocks
– Formed beneath surface
– Slow cooling produces
large crystals
– Coarse grained
• Extrusive igneous rocks
– Formed from lava on
surface
– Rapid cooling produces
small crystals
Igneous rock classification
•
Two factors
1.
2.
•
Nonferrous composition on
left of figure
–
–
–
•
Mineral composition
Texture
– Accumulated from rocks at various stages of breaking down
Low in density
Light in color
Granite: most common
example
Greater density
Darker color
Example: basalt
Sedimentary rocks
•
– Accumulations of silt, sand or other materials that settled out of water
• Clastic sediments
Ferromagnetic composition
on right
–
–
–
•
•
Sedimentary rocks
• Formed from particles or dissolved materials from previously
existing rocks
• Sediments
Chemical sediments
Formed from
dissolved rock
materials
Three sedimentation
paths
1. Chemical precipitation
from solution
2. Crystallization from
evaporating water
3. Biological sediments
Lithification
•
•
The rock-forming process
Two main parts
1. Compaction
•
•
Reduces thickness of deposit
Squeezes out water
2. Cementation
•
•
Spaces between sediment particles filled with chemical deposit
Chemical deposit binds particles together
Metamorphic rocks
• Previously existing rocks
changed by heat, pressure or
hot solutions into distinctly
different rock
• Causes associated with
geologic events
– Movement of the crust
– Heating and hot solutions from
magma intrusion
– Temperatures must be high
enough to cause
recrystallization, but not melting
The rock cycle
• Rocks transformed into new types by Earths’ interior
and exterior dynamical processes
– Moving continents
– Seas advance and retreat
– Weathered and eroded by wind and rain
Classification of metamorphic rocks
• Foliation
– Alignment of flat crystal flakes into sheets
– Caused by pressure on parent rocks
– Rock cleaves along planes between aligned grains
• Nonfoliated
– Parent rocks consist mainly of one mineral
– Grains not aligned into sheets