Ch 4b: Rocks Flashcards
How to identify rocks
look at texture, mineralogy and chemical composition
What is texture
pattern, internal patterning, orientation of the crystal
Mineraology
what are the minerals in it
Rocks
Solid, cohesive aggregate of crystals or grains of one or more. Exception: volcanic glass (non-crystalline rocks)
Types of rocks:
igneous, sedimentary, metamorphic
The rock cycle
Transition of a rock type into another rock type
Processes:
sedimentary, metamorphic, igneous
Sedimentary Process:
weathering, erosion, transportation, sedimentation, deposition, lithification, precipitation, diagenesis
Metamorphic Process:
re-crystallization, deformation
Igneous Process:
melting, crystallization
What is Igneous Rock
crystallizations from molten rock.
Two forms of igneous rock:
extrusive (shoots out of the top) and intrusive (doesn’t make it to the surface)
Plutonic Rocks
Intrusive Rocks
Intrusive rocks
magma cools below the Earth’s surface. Surrounding rock acts as insulator. Magma cools slowly.
Magma cools slowly
crystals have time to grow large, coarse grained (Phaneritic)
Phaneritic
if you can see the crystals with the naked eye
Volcanic Rock
Extrusive rock
Extrusive Rock
rapid cooling at the Earth’s surface in air or water.
Cools quickly and rapidly
microscopic crystals, fined grained (Aphanitic)
Aphanitic
cannot see individual crystals with the naked eye (volcanic glass)
Two types of Extrusive Rocks
Lava, Pyroclastics
Pyroclastics
“fire fragments”, molten rock and minerals, ash
Volcanic Ash
small minerals and volcanic debris. Unique to the volcano and the eruption.
Igneous Composition Types:
Felsic to Mafic, in between is intermediate
rock type depends mainly on the proportion of:
free quartz, feldspars, Fe-Mg minerals
Felsic
free quartz, pink, (Green = ultrafelsic) 800
Intermediate
half and half dark and light colors
Mafic
Darker 1200
Isotropic
equal properties and equal dimensions
eg. Magnatic
Anisotropic
there is preferred orientations, no equal properties and equal dimensions
eg. Sediment
Generalizations for Igneous
hard and isotropic due to crystalline texture, formed under conditions different at the surface. Brought to the surface via plate tectonics/volcanos
Regolith
unconsolidated rock layer
All rocks can be weathered by:
water, wind, ice, humans.
Rates are variable and controlled by:
properties of parent rock, climate, soil, time
Weathering
Break down of rocks at the Earth’s surface, chemical and physical
Erosion
Process that loosens and transports rock fragments
Physical Weathering
physical breakup of material, creating fractures, creates more surface area, no compositional change, stress applied exceeds strength
Examples of physical weathering:
biological weathering, ice, mineral crystallizations, human activities
Chemical Weathering
minerals are dissolving and/or chemically altered. Change in particle size (clays are usually made). Weaken the integrity of the material
Chemical Reactions
solution: dissolve carbonate minerals by adding carbonic acid
Hydrolysis: dissolve feldspars to form clays
Hydration: add water without releasing material
Oxidation: weathering of iron silicates to iron oxides
The more stable a mineral ….
the more slowly it reacts
Minerals that formed at a high temperature and pressure at depth are …
unstable at the surface
Sediments:
unconsolidated material can be loosened and transported. Sediment characteristics can tell us material movement distance and duration
Sedimentary Structures
many types: dunes ripples, bioturbation (filled tunnels), mudcracks
Define diagensis
physical chemical changes that occurs during the conversion of sediment to sedimentary rock
Sedimentary Rocks: clastic/detrital
derived from pre-existing rocks
Clastic:
Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock
Silt
gritty but falls apart
Clay
can be modelled
siltstone
if you break it, it has feathery wispy appearance
mudstone
breaks off into clumps
if its bigger than sands,…
its probably conglomerate
Soils
continued weathering of sediment: Naturally occurring, unconsolidated, mineral or organic, 10cm thick, at surface and can support plants
Soil development depends on:
climate, organisms, relief, parent material, time
Soil Structure:
distinct layers (horizons) are designated with modifiers (indepth horizons)
A horizon
zone of leaching or eluviation of mineral and organic matter. Maximum organic matter. Coarser texture than B
B horizon
Zone of accumulation or illuviation. Minerals (clay, oxides, salt) transferred from A
C horizon
Parent material, pre-existing sediment, shows some weathering due to soil processes.
Laterites:
wet, warm climates, deep red, highly leached clayey. Ultimate end product of chemical weathering. In the B horizon
If T and P increase due to:
increasing sediment layer thickness in basins, converging plates, proximity to hot magma bodies. Then enters metamorphsis.
Protolith
What you started with
Metamorphic Rocks
“changed form”. Recrystallized in the solid state. May involve deformation.
Bigger Mica =
More shiny
Metamorphism is caused by
change in pressure and temperature
Main types of Mrocks
Contact, Regional
Contact MRocks:
cooling of a plutonic body
Plutonic:
magma chamber that is localized deep in the Earth. Temperature changes but not pressure
Regional MRocks:
Stress and heating related to plate tectonics. Large scale changes, mountains.
If Temperature Increase…
partial melting (different minerals melt at different temperatures. Addition of water lowers melting T, increasing P raises melting temperatures.
Andesitic:
intermediate between felsic and mafic
Rhyolitic: Felsic flow
more SiO2, doesn’t flow well
Basaltic: Mafic flow
less SiO2, flows well
Pacific Ring of Fire
History’s famous volcanic eruptions. Major climate and weather changes.
Most significant of the volcanoes are the
Stratovolcanoes
Stratovolcanoes
Composite volcano.
Variable viscosity
Increased water content
Source of many volcanic hazards.
Phreatic
underground water in a zone of saturation
Large _____ eruptions can affect the global climate for several years
Pyroclastic-rich.
eg. Mount Pinatubo, PH, 1991
Height and amount of material emitted into the atmosphere can cause:
Reduced solar radiation (temporary).
Temperature drops related to SOx aerosols (Long-term)
Global Spread
Once in the stratosphere movement is global, effects become widespread
Volcanism is:
A suspected culprit for the Permian Extinction.
Tectonic Uplift
Creates obstacles that control atmospheric flow patterns.
eg. Rain shadow effect, chinooks, breezes.
Rain Shadow Effect
wet on one side of the mountain, dry on the other
Differential Heating
Plate tectonics changes relief.
Variable temperatures due to sun angles and heat capacity differences. Changes precipitation patterns
Uplift - Mass wasting
Steeper slopes promote material transfer, “land slides”
Effects of mass wasting
damming of rivers, removal of vegetation, soil disturbances
Carbon Cycle
Strongly affected by the rock cycle, common link between climate components.
Carbon Cycle: climate components
Weathering: removes it from atmosphere
Lithification: confines it
Biological Organisms: need it
Metamorphism and Volcanic Eruptions: release it
Describe the process of Diagenesis
Sediment piles become thicker –> increases compaction, fluids may precipitate out and cement the pieces together.
