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126 Cards in this Set

  • Front
  • Back
Meaning of the word 'Geology'.
Geo-Earth
Logia-Study/science
What things do geologists study other than rocks? (3)
Volcanism, glaciation, stream-flow.
What is the theory of 'Catastrophism'?
pre-1800 people though the earths features were produced by God, during catastrophic events.
Who were the first type of geologists?
Miners.
Who was the father of modern geology?
James Hutton (1726-1797)
What theory did the father of geology propose?
'Uniformitarianism' everything moves slowly in a repetitive continuous cycle.
When was the theory of tectonics proposed and then accepted?
proposed-1960/70
accepted 1980
What is the most abundant element in the earths bulk?
iron (Fe)
What is the most abundant element in the earths crust?
oxygen (O)
What is the earths inner core made of? How far below the surface is it?
Solid iron. 5000-6400km below the surface.
How thick on average is the oceanic crust?
8km.
How thick on average is the continental crust?
45km.
Which part of the earth generates the magnetic field?
The liquid outer core.
How were the zones of the earth discovered?
Vibrations through earthquakes and nuclear tests show the reflections and refractions of different waves through different material.
What is the earths outer core made of? How far below the surface is it?
Molten iron. 2900-5000km below the surface.
What is the temperature of the earths mesosphere (mantle)/core boundary? How far below the surface is the mantle?
5000oC. 350-2900km below surface.
Describe the Asthenosphere. (3)
100-350km below surface.
Part of the mantle.
Rocks are ductile, have little strength and easily deform.
Describe the Lithosphere. (3)
Outer 100km of the solid earth.
Uppermost mantle and crust.
Rocks are harder and more rigid than those in the asthenosphere.
What processes do plate tectonics generate? (3)
Earthquakes, volcanoes, mountain building.
What is the geothermal gradient?
The rate at which the earths temperature increases with depth.
What oC/km can the geothermal gradient be between?
15-40oC per km.
What is the surface heat flux?
0.1W/m2
What is the lithostatic pressure (weight of rock) in reference to geothermal gradients?
0.3 kbars/km
What is the hydrostatic pressure (weight of water) in reference to geothemal gradients?
0.1 kbars/km
What is the geothermal gradient in the UK? In South Africa? What does this mean?
In the UK it is 30oC/km. In South Africa it is 9oC/km, this means mines can be much deeper in Africa.
What is the density composition of the earth?
Low density crust is underlayen by higher density mantle, which is underlayen by higher density core.
What is the average geothermal gradient at the base of the oceanic lithosphere? What is the temperature?
13oC/km. 1300oC.
What is the average geothermal gradient at the base of the continental lithosphere? What is the temperature?
6.7oC/km. 1350oC.
What is a mineral? (4)
Naturally formed.
Inorganic.
Specific chemical composition.
Characteristic crystalline structure.
Give examples of minerals composed of a single element. (5)
Diamond (C). Graphite (C). Gold (Au). Copper (Cu). Sulfur (S).
What is Galena composed of?
PbS, lead sulphide.
What is a streak?
Colour of a thin layer of powdered material left when specimen is rubbed on an unglazed ceramic plate.
What is luster?
Quality and intensity of light reflected from a mineral.
Metallic luster-
like a polished metal surface.
Vitreous luster-
like glass.
Resinous luster-
like resin, the look of dried glue or amber.
Pearly luster-
the iridescent look of a pearl.
Greasy luster-
as if the surface were covered by a film of oil.
What is the Mohs scale?
A relative hardness scale using 10 minerals with distinct hardness.
What are types of tenacity are there?
Tenacity means resistance to being broken or bent. Brittle, elastic or flexible (plastic).
What is density? What is the unit?
Mass per unit volume. The unit of density is gram per cubic centimeter (g/cm3).
Minerals with a high density (gold) contain atoms with high mass numbers that are closely packed.
What is specific gravity?
The weight of substance in air divided by the weight of an equal volume of pure water. So specific gravity is a ratio of weight.
What is cleavage?
The tendency to break in preferred directions along bright, reflective planar surfaces. The planes along which binding between atoms is relatively weak.
What is the cleavage of Halite?
3 cleavages at 90o to each other. Cuboid shapes.
What is a crystal?
Any solid body that grows with planar surfaces.
What shape does quartz take?
Hexagonal crystals, prismatic form.
What shape does Jamesonite take?
Acicular, needle-like.
What shape does Mimetite take?
Botryoidal, grape-like.
What shape is a conchoidal fracture?
Ridged like a shell.
Recite the rock cycle.
At one time all rocks were igneous. Then they were exposed to wind and weather and broken down into grains, when they reformed into sedimentary rocks. These are then buried, put under high temperature and pressure which causes crystal type rocks.
Where do most carbonate minerals form?
In the sea.
What is an igneous rock?
They are formed through the cooling and solidification of magma.
What conditions are required for melting rocks? (3)
Depressurisation (driven by tectonic forces).
Adding water and other volatiles.
Heating to the point of melting.
What are the three magma types, their silicon contents and their temperatures.
Basaltic 45-55% silicon deficient, 1200oC.
Andesitic 55-65% silicon, 800-1000oC.
Rhylolitic >65% silicon rich, 600-900oC.
What % of magma is dissolved gasses, and what gasses are these?
0.2-3%, it is mostly water vapour, with some CO2.This mix accounts for 98% of volcano emissions.
What is the viscosity of magma dependant on?
Dependant on temperature and comosition.
The higher the temperature, the lower the viscosity.
The higher the silica content, the higher the viscosity, due to the bonding of silica.
What is crystalisation?
When magma cools it produces crystals. Different magmas produce different minerals, which crystalise at different temperatures.
Describe intrusive rocks.
Coarse grained because of slow cooling within the crust.
Describe extrusive rocks.
Fine grained as it solidifies on the surface, cools rapidly, not enough time for large crystals to grow.
What are phenocrysts?
Crystals that start growing earlier form larger crystals. The isolated large grains are called phenocrysts. An igneous rock containing phenocrysts is called porphyritic (nearly all abdesitic rocks).
What are vesicles?
t the last stages in solidification, the bubbles become trapped and preserved, called vesicles.
What are amygdales?
Vesicles filled by secondary minerals are called amygdales.
What types of volcanoes does basalitic magma produce?
Sheild volcanoes. Broad and gently sloping, as the low viscosity can flow for km down gentle slopes.
What are the types of tephra and their measurments? (3)
Bombs (64mm).
Lapilli (2-64mm).
Ash (<2mm).
What do andesitic eruptions emit? (2)
Viscous lava flows.
Tephra.
What is a stratovolcano?
Layered volcano formed through the release of lava then tephra then lava ect.
What is the texture of the igneous rock phanerite?
Course grained.
What is the texture of the igneous rock pegmatite?
Contains large mineral grains 2cm+.
What is the texture of the igneous rock aphanite?
Fine grained.
What is a pyroclastic flow?
A mixture of hot gasses and pyroclasts which are more dense than the atmosphere, which the mixture flows down the flank of the volcano.
What is a rhyolitic eruption?
A circular steep walled basin, created by collapse of surface rock following an eruption. This would wipe out whole areas of the globe.
How are glassy rocks formed?
When magma cools quickly, the atoms do not have time to arrange themselves into minerals, form black glass.
What are the minerals common igneous rocks are made up of? (6)
Quartz. Feldspar (potassium and plagioclase). Mica (muscovite and biotite). Amphibole. Pyroxine. Olivine.
What minerals are a lightly coloured igneous rock likely to be made up of? (3)
Quartz. Feldspar. Muscovite. These minerals contain a lot of silicon.
What minerals are likely to be found in dark coloured igneous rocks? (3)
Biotite. Amphibole. Pyroxene. These mineral contain less silicon.
What are plutons?
Bodies of intrusive igneous rock, regardless of shape or size.
What is a dyke?
A thin but laterally extensive igneous rock intrusion that cuts across the layering of the rock into which it intrudes. (minor intrusion).
What is a sill?
An igneous intrusion like a dyke, but runs parallel to the layering of the rocks into which it intrudes.(minor intrusion).
What is a laccolith?
An igneous intrusion parallel to the layering of the rocks, but forces the layers above it to bend, forming a dome. (minor intrusion).
What is a volcanic pipe?
An igneous intrusion which is roughly cyldrical and once fed magma upward to a vent.(minor intrusion).
What is a batholith?
The largest kind of igneous intrusion. Iregular shape. Cuts accross the fabric of the rock that it intrudes into. (major intrusion).
What is a xenolith and how are these produced?
Any rock still enclosed by a magmatic body when it solidifies. Caused when rising magma dislodges fragments of overlying rocks, which being cooler and denser will then sink.
What are kimberlite pipes the main source of?
The worlds diamonds.
What are sediments transported by? (4)
water, ice wind, gravity.
What is stratification?
Bedding layers. Stratum (singular) Strata (plural).
What are clastic sediments?
Loose fragments of rock debris produced by physical weathering.
What are the properties of course clastic sediments?
Made up of minerals least susceptible to weathering, such as quartz and potassium feldspar.
What is the roundness describing?
The sharpness of the edges of a rock.
What is sphercity describing?
How closely the rock resembles a sphere.
What is lithification?
The process of creating sedimentary rock. Diagenesis is the term for the processes that casue lithification.
What are the processes of diagenesis? (5)
Compaction, cementation, recrystalization, dissolution, chemical alteration.
Name some clastic sedimentary rocks. (5)
Conglomerate, breccia, sandstone, siltstone, mudstone.
What is bioturbidation?
Mixing of sediment by living creatures.
What are mudcracks evidence of?
Subaerial exposure.
What are evaporites?
Rocks made from salts produced by evaporation.
How are banded iron deposits formed?
When the earths atmosphere was switching from reducing to oxygenating.
What type of rocks are chert and flint and how were they formed?
Hard compact sedimentary rocks composed almost entirley of fine grained quartz.Tend to occur in limestones.
How are phosphate deposits formed at what are they used for?
Produced from animal droppings. A main source of fertiliser.
What is the difference between biogenic sediments and bioclastic sediments?
Both are made from fossils, But bioclastic are broken and scattered.
Describe deep sea ooze.
Fine grained, deep sea deposit of skeletal material made of mainly calcium carbonate and silica.
Which is the most important biogenic rock?
Limestone.
What is chalk composed of?
Compacted carbonate shells of minute floating organisms.
What is oolitic limestone?
Contains spherical grains of carbonate. Formed when the grains are rolled forwards and backwards in a tidal environment.
How is coal formed?
Plant remains accumulate to form a pure sediment, peat. This is compressed into coal.
What is stratigraphy?
The study of a sequence of events.
What is the law of orginal horizontality?
Water layed sediments are deposited in strata that are horizontal.
What is stratigraphic superposition?
Any sequence of sedimentary strata was deposited from bottom (oldest) to top (youngest).
Describe the types of unconformaties. (3)
Unconformity- a substantial break or gap. Angular unconformity- old strata deformed then cut off by erosion, then new layers deposited ontop. Disconformity-irregular surface of erosion between parallel strata, hard to see. Nonconformity- strata overlie igneous or metamorphic rock.
What is the primary unit of geological time?
Geological period, a time during which a geological system accumulated.
How is the age of the earth measured accurately?
Through radioactivity. Discovered in 1896.
Why is radiocarbon dating useful?
For dating geologically young samples, its half life is 5730 years.
Magnatism can be used to date rocks, how?
Magnetite and other iron bearing minerals can become permanently magnatized above a certain temperature called the Curie point.
What do vertical changes in strata reflect?
The passage of time.
What are alluvial fans made of, and how are they formed?
Conglomerates and sandstone. Form where mountains join plains because of a change invelocity of the river, there is no longer enough energy to carry the material.
What are the properties of glacial sediment?
Random mixture of particles that range in size, often angular and striated. Only glaciation can carry huge boulders.
What are pelagic facies?
Deep oceanic sediments.
What are deep sea fans?
Large subamarine canyons.
What are lacustrine facies?
Lake sediments.
What are eolian sediments?
They are windblown sediments, the finest type of sediments.
What is metamorphism?
Rocks changing in response to changes in temperature and pressure. It starts at 200oC and ends when most rocks melt at 650-800oC.
What are the general effects of P and T?
With increasing temperature, water is expelled from minerals, carbon dioxide is expelled from carbonates, the minerals become coarser.
What is low grade metamorphism?
Occurs between 200-500oC at relativley low pressure.
What is high grade metamorphism?
Occurs at above 500oC at relativley high pressure.
When does differential stress occur?
If pressure is different in different directions. It results in the rock developing a planar fabric known as a foliation.
What is the relationship between fluids and metamorphism?
Fluids are usually present. Direct evidence of this are mineral filled fractures called veins. Metamorphism progresses more quickly when fluid is present.
Give examples of high, medium and low grade metamorphisised rocks.
High- schist and gneiss. Medium-phylite.
Low-slate.