- Created by: Alex Hegarty
- Created on: 30-04-12 14:03
Minerals can be formed in a numberof environments, the key idea is that minerals must be crystallised because they are formed from other rocks.
These can be formed in a number of ways
- Crystallisation from a melt (All from the same Magma Random Interlocking crystals)
- Metamorphic recrystallization (A Re-order of atoms)
- Crystallization of a solution (A solution evaporate and leaves behind a crystal for example in a salt lake)
- Crystallization as cement from flowing water (Minerals dissolve into rain water and when a suitable pH is found is formed)
- Crystallization of thermal fluids (Within a vein Crystals point inwards like teeth)
These can be very valuable especially if they are lustrious (SHINY SHINY) or very strong like diamonds.
Minerals are naturally occuring elements or compounds with fixed properties
Rocks are naturally occuring materials formed from fragments of rocks or fossilised creatures....
Fossils are any preserved signs of life which are past 10,000 years old.......
Sedimentary Rocks (Shallow Marine)
Sedimentary rock type can differentiate depending on the environment in which they are deposited..... In a shallow marine environment sedimentary rocks formed would be.....
- Limestone this rock is composed mainly of calcite and the skeletal remains of dead sea creatures
- Sandstone, well its made of sand, y'know from the seabed
- Conglomerates are sediments formed of Rounded clasts
Sedimentary Rocks (Deep Marine)
Sedimentary Rocks formed in a deep marine environment are
- Turbidites are rocks which have been formed when low celocity waters have deposited sediments on the ocean floor and are usually banded have ripple marks, and are sorted by density.
- Black shales
Sedimentary rocks (Land)
Sedimentary rocks found on land can vary massively.....
Deposited by Rivers and deltas - Shales and sandstones and coal.
Deposited by wind and water - Breccias and desert sandstones.
Evaporites - Halite
Glacial till - can vary greatly.
Reef building corals
These are usually found in Marine environments which are shallow and warm.
Trilobites are usually found in marine environments.
Ammonites are usually found in marine.
Plant fossils can indicate past life on land, for example fern fossils.
Trace fossils are tracks or burrows basically a marking which indicates that something has been there before.
Igneous rocks are rocks which have been heated to the point of melting, and then cool. This means there is a direct correlation inbetween the size of crystals and how quickly the rock has cooled. If the crystals are large then the rock cooled slowly if they're small it cooled quickly.
Metamorphic rocks are caused by putting temperature and pressure on pre-existing rocks.
Rock records can be used to provide an accurate account of tectonic activity.
Breaks in these rock records are called uncomformities.
Carbon dating can also beused or by measuring the decay of certain radioactive materials.
Folding and faulting
Folding and faulting are both easily observable if we use the principle of original horizontality.
Folding is caused by tectonic stress (compression)
Faulting is caused by tectonic stress (compressional, sheer and tensional)
This is the belief that the rock on the bottom is the one which was placed their first. Though in certain situations the rock can be tilted to a point where it is completely upside down.
This is the belief that all rocks are positioned horizontally, but sand dunes can disturb this slightly.
Cephalopods evolved in a manner which makes it easy to use them to date rocks.
Beginning as Goniatites then becoming ceratites and then finally ammonites.
After they become ammonites it is possible to use the suture line to distinguish their evolutionary period.
Graptolites can also be used to date rocks through use of their evolutionary chain.
They start off with many stipes (the branches) and then evolve to have only two. Then the thecae (spikes) begin to poin inwards and then they become just one stipe.
Weathering is the process of eroding rocks and breaking them down. Usually in one of three ways physical chemical or biological.
Chemical weathering - Of limestone or of sand and clay.
Biological weathering - By means of roots or by organic acids.
Physical weathering - By freeze thaw method.
This is the process of transporting materials of weathered products.
Water ice and wind can erode rocks by methods of attrition and abrasion.
Sediment is transported and deposited.
When gravity s in place it can cause rocks to gather at the foot of hills and create scree slopes.
V shaped valleys are caused by rivers.
U shaped valleys are caused by Glaciers.
Low lying floodplains are usually in lowland areas.
These valleys may not reflect the underlying geological site.
landforms caused by weathering
When rocks of different types are eroded they erode at different paces and thusly landforms are created in accordance with how they erode.
- Plateau - Horizontal beds
- Scarp and vale - Gently dipping beds
- Ridge -Steep dip Dyke
- Upland area - Pluton
- Fault scarp
- Coastal landform - Cliffs
Landscape can be modified by previous business there for example a quarry, and this does not indocate weathering.
SSSI & RIGS
SSSI's or sites of specific scientific interest.
RIGS or Regionally important Geological sites.
These kinds of sites are not to be damaged because they are of specific importance.
Catastrophism & Gradualism
These are used to indicate features that take place at different rates. Catastrophism are things that happen exceedingly fast, for example a meteorite strike.
Gradualism are thing that happen well gradually, like a river eroding its bed.
The earths crust
The earths crust consists of the Crust, mantle, outer core and then inner core. The asthenosphere is the tectonic plates which make up the crust. The lithosphere is the cold rigid outer shell which stretches down to the mantle.
The plate boundary types are
- Divergent - Otherwise known as a constructive plate margin.
- Conservative - Where plates slide past each other causing earthquakes.
- Convergent - Destructive plate margins where plates slide into each other and then one is subducted beneath the other.
Global warming is the process of the earth warming up due to greenhouse gases in the atmosphere. We can see that the level of CO2 is rising from checking cores of ice found, or from previous global sea level change for example submerged forests. CO2 can be contained in trees and in limestone and is released from them when they are gone.
Origins of life
Life probably originated from Hydrothermal pools or Black smoker approximately 3500Ma.
These rocks provide evidence of the changing latitude of Britain.
1. Lower Palaeozoic period - Britain is south of the equator and this can be used evidence for plate collision. Proof of this is the presence of both turbidites and granites and thrust folds.
2. Upper palaeozoic period - Britain drifts to be above the equator, the tropical seas at this time can be seen through the presence of limestones. Swamp forests and this can be seen coals. Desert conditions can be seen through evaporites and Breccias.
3. Mesozoic period - seperation of africa from America, the warm seas can be seen from the limestone.
4. Cenozoic period - Opening of north atlantic, diverging plate boundaries in NW britain can be seen in the sudden volcanism and also glaciation presnt at the time.
The hazards of geological events
- Earthquakes - can cause landslides.
- Volcanic eruptions - Lava ash and pyroclastic flows
These factors relate to how dangerous it can be
- Population density
The low level of accurate hazard prediction means it can be hard to tell when a geological disaster is going to occur.
Recent major finds...
- Rare exceptionally well preserved - Burgess shal fauna
- Links in evolution - Archaeopteryx
- Complex fossils
- Very early hominids - Lucy
- Exceptional discoveries
gas and Oil migration
Gas and Oil migrate through rocks depending on their porosity.
The change from source beds to reservoir rocks through differing porosity.
Oil and gas are most likely to be trapped by cap rocks faults or salt domes.
Seek anomalies in background data for example high magnetism or chemical levels.
Sample and analysis of river beds or soil.
Siting dams and reservoirs
Factors which affect the ability to site dams and reservoirs.
- Permeability of bedrock
- Dip of strata
- Faulting and jointing
- Bedrock stability
environmental geoscientists do.......
- Planning for and monitoring of waste disposal
- Restoration of soil
- Monitoring of potentially polluted water.
A geotechnical geologist investigates the stability of bedrock, to check if certain geological thingamabobs can be built there for example Dams.
Academic research geologists
These geologists are the more lab based ones mainly reviewing work already done and reviewing it.