Notes for first exam
Minerals
Isotopes - elements with different numbers of neutrons in the nucleus
Ions - atoms with excess positive or negative charge (gain or loss of electrons from the outermost shell).
- Ions dissolved in water will combine to form compounds.
Cations (positive charge, lose electrons) Ca+
Anions (negative charge, gain electrons) CO3 Compounds - combination of atoms of one or more elements in a specific ratio.
Types of Bonds
1. Van der Waals weakest bond- weak attraction. (Graphite)
2. Ionic - transfer of electrons between cations and anions. Sodium Chloride (salt), NaCl
3. Covalent strongest bond- electrons are shared between atoms. (Diamond, Quartz))
Most Common Elements – the most common elements on our planet, by weight, are Oxygen and Silicon.
They combine and become part of the largest family of minerals, the SILICATES.
1. Oxygen
2. Silicon
47%
28%
Five Requirements to be a mineral
1. Naturally formed
2. Solid
3. Formed by inorganic processes
4. Specific chemical composition
5. Characteristic crystal structure
Properties of Minerals
1. Crystal form –The shape of an individual mineral crystal and is a reflection of the internal
arrangements of atoms.
2. Habit – The shape of a single or group of mineral crystals.
3. Cleavage – a smooth break producing what appears to be a flat crystal face. This break is along a
plane of weakness in the crystals atomic structure.
4. Luster – a description of the way light interacts with the surface of a crystal. For your class we will
define a luster as being metallic or non-metallic.
5. Color – Not good for identifying minerals. Trace amounts of impurities can give a mineral different
colors.
6. Streak - The color of the mineral in its powdered form. This is a true indication of a minerals color.
7. Density – The weight per volume of a mineral.
8. Hardness - The resistance of a mineral to be scratched. The stronger the bonds, the harder the
mineral
Mohs Hardness Scale (unit less) this scale is used to determine the RELATIVE hardness of minerals helps
in their identification.
The scale is numbered 1-10 with small numbers being soft minerals and large numbers being hard minerals.
Igneous Rocks
Rock – a coherent, naturally occurring solid, consisting of an aggregate of one or more minerals, or a mass
of natural glass or organic matter.
Basic Rock Classifications
•Igneous
•Sedimentary
•Metamorphic
Igneous Rocks
-a rock that forms when hot molten rock
(magma or lava) cools and freezes solid
Two types of igneous rocks
•Plutonic – cools underground
•Volcanic – cools above ground
Factors controlling Melting
1. Temperature: Melt at [800oC and 1200oC]
Source of heat [radioactive decay]
Partial Melting - Some minerals melt at a lower temperature than others.
Geothermal Gradient – the rate at which temperature increases with depth in the Earth.
2. Pressure: as pressure increases, melting temperature increases.
Lowering pressure causes melting in divergent margins.
3. Water content: as water content increases, melting temperature decreases
Water in rocks causes melting in convergent margins.
Bowen’s Reaction Series: There in an order in which different minerals crystallize. Usually, the dark
colored-mafic minerals crystallize first as a magma freezes. Likewise, they are the last to melt as a rock
heats up.
Types of Molten Material
1. Magma – molten material below the Earth's surface.
2. Lava – molten material above the Earth's surface.
Magma Chemistry
Molten material can consist of liquid rock, mineral grains and gases (H2O, CO2, SO2).
Silicon and oxygen (SiO2) make up the majority of a magma.
45% SiO2 - "low" silica content
75% SiO2 - "high" silica content
•Mafic – low SiO2; high iron and magnesium
•Silicic – high SiO2; low iron and magnesium
Magma Viscosity
Viscosity – resistance to flow
honey – high viscosity
water – low viscosity
•Viscosity increases as silica content increases.
Igneous Rock Types
•Intrusive (plutonic) rock – cools and solidifies below the Earth's surface.
•Extrusive (volcanic) rock – cools and solidifies above the Earth's surface.
Textures of Igneous Rocks
Texture – overall appearance, related to size, shape, and arrangement of minerals.
Texture is related to cooling history of an igneous rock, not its chemistry.
There are two main terms for igneous rock textures
• Phaneritic – Slow cooling that results in crystals big enough to see with the unaided eye.
• Aphanitic – Rapid cooling that results in crystals too see with the unaided eye.
Two special Aphanitic textures are:
Vesicular: this rock contains small cavities left as gas bubbles froze.
Glassy: this rock looks like dark brown or black glass and is created when the lava cools so
fast the almost no crystals form.
Volcanoes and Volcanism
Volcano - a vent through which magma, solid rock debris, and gases are ejected.
Classified by the type of eruption:
Largely a function of viscosity and dissolved gas content of the magma.
Viscosity – the resistance of a liquid to flow. Magma/Lava with a high silica content have a high
viscosity (they are thick, not runny). Silicic melt has a high viscosity.
1. Non -explosive - low viscosity (flows easily)
- low silica content (mafic)
- basaltic magma/lava
Associated Landforms
1. Shield Volcanoes - broad, flat volcano with gently sloping sides, built of successive lava flows.
2. Basalt Plateaus (flood basalts) - lava emerges from elongate fractures or fissures and spreads widely to
create vast, flat lava plains, sometimes covering 10's or 100's of thousands of square kilometers.
2. Explosive- high viscosity (resists flow)
- high silica content (intermediate, felsic)
- andesitic or granitic magma (lava)
Associated Landforms
Composite Cones - large, nearly symmetrical
- built by alternating layers of lavas and pyroclastic fragments
- most violent
- Mt. Saint Helens, Mt. Rainier
- Located at converging oceanic – continental plate boundaries
Crater - a funnel shaped depression near the summit of a volcano.
Caldera - a large crater, usually greater than a kilometer across.
Pyroclastic flow- hot pyroclastic material and gases which rush down the flanks of a volcano
Lahar - hot and cold liquid and debris
Pyroclastic Rocks (Tephera)
Bombs – largest
Lapilli - intermediate size
Ash - smallest
Lava types
pahoehoe - (pronounced pah-hoy-hoy), relatively smooth skin
aa - (pronounced ah-ah), rough surface, jagged blocks
Why are some explosive while other are not?
Explosive volcanoes has a magma composition which is high in silica while non-explosive volcanoes are low
in silica. High silica magma is thick and allows for more gases to be trapped within them. When the
pressure confining the magma is released the gases evolve explosively.
Hazardous Volcanic Geologic Processes
Tephra Fall
-Mixture of hot gas and fragments less dense than air.
Major Hazards of Tephra Fall
1.Impacts
2.Burial of structures
3.Suspension of abrasive aerosols
Pyroclastic Flows
Avalanches of hot, dry, volcanic rock fragments and gases
•Denser than air
• 600 - 1500O F
• Up to 200 mph
• Tends to channel into valleys
Major Pyroclastic Flows Hazards
•Incineration
•Burial
•Impacts by rock or flying material
•Exposure to noxious gases (SOx) (CO2)
Explosive Ejection of Ballistic Projectiles
Material is projected along arced trajectories
• Not constrained by wind direction
• Not dependent on eruptions
• Large projectiles thrown 1/2 mile
Lateral Blasts
The horizontal projection of material due to pressure release
Lava Flows
• Flow controlled by topography
• Destructive, but not life threatening
• Speed related to slope and viscosity
Lahars
• Rapid flow of sediment, rock, and water
• Channelized
• Twice as fast as water
Plate Tectonics
The Prune Effect - 1800s
The molten Earth cools and contracts
The crust wrinkles and crumples
Mountains form
Problems
What about rift valleys?
What about shape and position of the continents?
The Expanding Earth
20th century - radioactive decay
Land masses are ripped apart
Explains the continents
Problems
What about the mountains?
Continental Drift
An idea before its time
- Alfred Wegener 1915
- Processor to plate tectonics
Pangaea – supercontinent (200 million years ago)
Land fragmented and floated around
Lines of Evidence for Continental Drift
1. Matching Coastlines
2. Matching Geology
3. Glacial Striations
4. Fossil Evidence
Glossopteris
Mesosaurus - links South America and Africa during the late Paleozoic and early
Mesozoic eras.
5. Apparent Polar Wandering
- The Earth has a magnetic field. This creates an invisible force field in space. We can detect this
field with a compass -- a compass needle aligns with magnetic field lines.
- We can represent this field by an arrow that points from the north magnetic pole to the south
magnetic pole, through the center of the Earth.
- Geologists discovered that rocks contain tiny magnetic mineral grains, each of which acts like a tiny
compass needle and points to the Earth's magnetic poles.
- When an igneous rock, like basalt, forms, these needles (representing the magnetization of the
magnetic grains) align with Earth's field and lock into place.
- The magnetization of recently-formed lavas points toward the present-day magnetic poles (which is
near, but not exactly at the geographic poles).
- But the magnetization in older rocks does not point toward MNP.Why not? One possible
explanation would be that the location of the magnetic pole has changed through time, an idea known
as polar wandering.
- Geologists measured magnetism in rocks of different ages in North America and constructed a
polar-wander path (PWP), to show how the pole had moved through time.
- They did the same for rocks in Europe and found that the PWP is different from the PWP for North
America. This didn't make sense!
- So, polar wandering does not occur!! The magnetic pole doesn't wander. The pole stays fixed, and
continents move. So, we call the trace of the pole relative to the continent and "apparent polar-wander
path."
- The occurrence of apparent polar-wander paths means that continental drift does occur.
Unifying Theory - Plate Tectonics
Tectonic cycle- deals with the movement and interactions of the lithospheric plates. The theory describing
the movement of the continents and the mechanism which drives them. It brings together two earlier
theories (continental drift and sea-floor spreading). This is the “Unifying” theory of geology and explains
many of the landforms we see and processes which form them.
Plate Boundaries / Margins
Divergent Plate Boundaries
1. continental - rift valleys
2. ocean - mid-oceanic ridge / spreading sea floor
Transform Plate Boundaries
Convergent Plate Boundaries
1. Oceanic - Continental
2. Oceanic – Oceanic
3. Continental - Continental
Convergent - when two plates move toward one another, they form either a subduction zone or a continental
collision. This depends on the nature of the plates involved. In a subduction zone, the subducting plate,
which is normally a plate with oceanic crust, moves beneath the other plate, which can be made of either
oceanic or continental crust. During collisions between two continental plates, large mountain ranges, such
as the Himalayas are formed.
Divergent - linear feature that exists between two tectonic plates that are moving away from each other.
These areas can form in the middle of continents but eventually form ocean basins. Divergent boundaries
within continents initially produce rifts which produce rift valleys. If the rifting process stops, a failed rift
results. Therefore, most active divergent plate boundaries are between oceanic plates and are often called
oceanic rifts.
Transform fault - a fault which runs along the boundary of a tectonic plate. The relative motion of such
plates is horizontal in either left or dextral right. Typically, some vertical motion may also exist, but the
principal vectors in a transform fault are oriented horizontally.
Weathering
Three Dynamic Processes of Breaking and Removing rock
1.Weathering - the disintegration and decomposition of rock at or near the surface
2.Erosion – the movement of weather material
Result of Weathering
Regolith – a loose layer of broken rock and mineral fragments.
Dissolved ions
Benefits of Weathering
Creates soil
Produces clay, sand, and gravel
Produces minerals
Types of Weathering
Mechanical – physical breakdown of rocks.
Chemical – decomposition of rocks by chemical reactions.
Mechanical Weathering
1.Frost Wedging
2.Salt Wedging
3.Biological Wedging
4.Unloading
5.Thermal Expansion
1. Frost wedging – water penetrates into cracks, expands when it freezes.
Must have:
•Adequate moisture
•Cracks in rocks
•Freeze/thaw cycles
2.Salt wedging – growth of minerals in cracks
•Desert environments
•Water evaporates, ions in solution combine to form minerals
3. Biological wedging – plant roots penetrate into cracks causing cracks to widen.
Must have:
•Climate hospitable for plants
•Adequate moisture and temperature
4. Unloading - removal of pressure of deep burial
•Exfoliation Domes
•Sheeting
5. Thermal expansion
•repeated daily heating and cooling of rock;
•heat causes expansion; cooling causes contraction.
Chemical Weathering
Results in new minerals and ions in solution.
Water and acid are essential.
Types of Chemical Weathering
Hydrolysis - any reaction in which water participates.
1.Ion Exchange – H+ replaces other cations.
2.Dissolution - mineral completely dissolves, leaving only ions in solution.
3.Oxidation - reaction in which elements gain or lose electrons (example: rust).
Factors influencing Weathering Rates
1.Rock Structures – chemical/mineral composition, Physical features
2.Topography
3.Climate
Erosion – transport of regolith from one place to another
Modes of Transport
1.Water
2.Wind
3.Ice
Transport by Water
Saltation – particles move downstream in short jumps.
Bed load – material transported by saltation.
Suspended load – material carried in water for long distances.
Erosion by Wind
Deflation - Loose material can be picked up by wind
Abrasion - windblown sediments can "sandblast" rocks.
Transport by Wind - Same processes as water – saltation, bed load and suspended load.
Erosion by Ice
Plowing – loose material is "bulldozed".
Plucking – pieces of bedrock are pried loose.
Abrasion – pieces of rock in the ice grind against bedrock below.
Particle size and method of Transport
Water – smallest particles to small boulders.
Wind – smallest particles to sand size.
Ice – smallest particles to boulders as big as a house.