Download Geology 101

Geology 101
Sarah Arnoldi
 Plate Tectonics
 Geological Time
 Minerals
 Volcanoes
 Igneous Rocks
 Sedimentary Rocks
 Metamorphic Rocks
 Groundwater
 Global Climate Change
 Mineral Resources
1
Chapter 3
Minerals
2
Defining a mineral
1. Naturally occurring
o True minerals are naturally occurring whereas synthetic gemstones are generated by
artificial/ human-made processes and not minerals
2. Inorganic
3. Solid substance
4. Crystalline structure
o Atoms are arranged in an orderly, repetitive manner
5. Definite chemical composition that allows for variation
Definitions
 Rock: solid mass of any mineral, or mineral-like matter that occurs naturally
o Some rocks can be made entirely of one mineral. Eg limestone → calcite
 Aggregate: minerals are joined in such a way that their individual properties are retained
Atoms and bonding
 Atoms: smallest particles that cannot be chemically split. Contain protons and neutrons in a central
nucleus that is surrounded by electrons
 Protons and electrons have electrical
 Neutrons (charge 0)
charge
 Electrons (charge -1)
 Protons (charge +1)
 Atoms bond under the conditions (temperatures and pressures) that occur on Earth
 Chemical bond: transfer or sharing of electrons that allows each atom to attain a full valence shell
of electrons
 Ionic bonds:
o Forms ions – positively and negatively charged atoms and symmetrically distributed
o Bond is the attraction of oppositely charged ions to one another
o Complete transfer of electrons between atoms
 Covalent bonds:
o A chemical bond formed by the sharing of one or more valence electrons between a pair of
atoms
o Strongest type of bond
 Metallic bonds:
o Valence electrons are free to move from one atom to another so all atoms share valence
electrons. Relatively weak
o Accounts for the high electrical conductivity of metals
o Found in copper, gold, aluminium and silver
 Hybrid bonds:
o Incomplete transfer of electrons that results in atoms partially transferring and partially
sharing electrons
3
Mineral
Colour/Streak
Lustre
S.G
Cleavage
Fracture
Hardness
Other
Group and
structure
Medium
None
Conchoidal
6.5-7.5
Mafic
Silicate
→ Single/
Independent
tetrahedral
Vitreous to
dull
Medium
2
At 60° and
120°
Irregular
5-6
Mafic
Silicate
→ Double chain
Vitreous to
dull
Medium
2
At 90o
Irregular
5.5-6.5
Mafic
Silicate
→ Single chain
Vitreous to
sub metallic
Medium
1
At 180o
Irregular
2.5
Mafic
Silicate→ Sheet
Felsic
Hexagonal crystals
Silicate
→Threedimensional
framework
Green
Olivine
Vitreous
No Streak
Amphibole
(hornblende)
Brown,
Greenish
Black
Grey-White
Streak
Brown, Black
Pyroxene
(augite)
Biotite Mica
White Streak
(rare)
Brown, Black,
Transparent
Grey Streak
White, Grey
Quartz
No Streak
Vitreous to
waxy
Medium
None
Conchoidal
7
4
Mineral
Colour/
Streak
Lustre
Fracture
Hardnes
s
S.G
Cleavage
Irregular
4
Other
-Fluorescent
under UV
Group and
structure
Fluorite
Clear light
green / white
Vitreous
Medium
4 good to
perfect
Octahedral
Pyrite
Brass-yellow
/ greenishblack
Metallic
Heavy –
Very Heavy
N/A
Irregular
~6-6.5
Opaque
Sulphide
Galena
Silver-grey /
silver-grey
Metallic
Very Heavy
3 perfect @
90°
Irregular
~2.5
Opaque
Sulphide
Magnetite
Earthy black
to reddish
brown / black
Dull-earthy
to submetallic
Heavy-Very
Heavy
5.5-6.5
Octahedral or
granular habit,
magnetic
Oxide
Haematite
Silvery-grey /
reddishbrown
Metallic
Heavy-Very
Heavy
5.5-6.5
Reinform,
botryoidal or
massive habit
Oxide
None
Irregular
None
Irregular to
subconchoidal
-Cubic or
octahedral
Picture
Halide
5
Chapter 4
Volcanoes
6
A volcano is…
 An opening in the Earth’s crust through which material from within the Earth escapes onto the
surface
 Part of the way the planet is still cooling – vents/safety values in the crust
 Features of the volcanoes depend on the nature of the original magma
Nature of Magma
 Is determined by:
 The chemical composition
 The temperature
 The dissolved gases
 These three factors determine the VISCOSITY (the ability to flow) of the magma
 High viscosity = flows slowly like a syrup/honey
 Low viscosity = flows quickly and easily like water
Viscosity
 Temperature:
 Hotter magma flows easily – is less viscous
 As magma cools it thickens, flows more slowly and solidifies quick – higher viscosity
 Chemical composition:
 Silica content
 Low silica content = low viscosity. Basaltic lavas have low silica so flow easily
 Higher silica content = higher viscosity. Granitic lavas have high silica so don’t flow,
and produce larger/bulkier features
Gas Content
 High gas content = high viscosity
 More explosive because the gases get trapped and build up pressure
 As the magma moves to the surface, the confining pressure is reduced and gases can release
suddenly
 Low gas content = low viscosity
 Any gases present are able to slowly leak out without building up pressure
Relationship between lavas, silica content, viscosity and gases
Basic/Mafic
Basaltic
Andesitic
Silica (%)
40
50
Viscosity
Low (sticky)
Gas
Least (1-2%)
Eruption
More frequent but gentle
Material
Lava/stream
60
Acidic/Felsic
Rhyolitic
70+
High
Most (4-6%)
Less frequent but violent
Pyroclastic, gases, lava
7