Elements, minerals and rocks Flashcards
What is an element?
A substance made entirely of one type of atom.
How can Earth’s elements be classified?
The Goldschmidt system.
Define the atomphiles and give some examples.
Gas loving elements, which occur as liquids/gases at temperatures/pressures found on/above the Earth’s surface. Examples may include nitrogen, hydrogen and carbon.
Define the lithophiles and give some examples.
Rock loving elements which combine with oxygen to form low-density compounds which remain near Earth’s surface and are concentrated in the crust. Examples may include oxygen, silicon and sodium.
In the lithophiles what are the eight elements in this group and how much do they account for the weight of the Earth’s crust. (Same for silicate minerals)
-Oxygen (47%)
-Silicon (28%)
-Aluminium (8%)
-Iron (5%)
-Calcium (3.5%)
-Sodium (3%)
-Potassium (2.5%)
-Magnesium (2%)
Silicon and oxygen combine together and also with other elements to form what?
The Silicate minerals.
Define the chalcophiles and give some examples.
Ore-loving elements combine with sulphur to form higher density sulphides. They occur deeper than lithophiles and are concentrated in the mantle. Examples may include copper, lead and sulphur.
Define the siderophiles and give some examples.
Iron-loving elements that have a high density and combine more easily with iron than oxygen, forming dense compounds that occur in the Earth’s core. Examples may include iron, iridium and nickel.
What can the bulk composition of the Earth be postulated from?
Meteorites.
What are the types of meteorite and what are their compositions?
-Iron meteorites=composed of iron and nickel.
-Stony meteorites=composed of silicate minerals and are non-metallic.
What is undifferentiated?
Smaller bodies cooled and solidified too quickly for differentiation to take place, so these primitive meteorites are our best picture of the early history of the solar system since they have fewer influences for change over the age of the solar system.
What is differentiation?
As a larger body cools, more dense materials such as iron sink towards the centre.
What are undifferentiated stony meteorites also known as?
Chondrites.
What is a mineral?
A solid, inorganic and naturally occurring chemical compound/element with a defined structure and composition.
What are the distinct characteristics of minerals?
-Chemical compositions
-Atomic structures
-Physical properties by which they may be identified
What are the two main element groups?
The two main element groups are the major elements and the minor elements.
What is the main process that forms minerals?
Crystallisation
What happens when water is 0 degrees celcius?
The temperature decreases, so crystals of ice start formation.
What happens when magma starts to cool and then when it cools below its melting point?
Solid minerals crystallise. When magma cools below its melting point, crystals of minerals begin to form.
When can this process occur and what happens if this continues?
When liquids evaporate from a solution. When water evaporates, the concentration of salt is a lot higher, so the solution becomes saturated. If continual evaporation occurs, salt will precipitate/drop out of solution a crystals.
What are the main physical properties of minerals?
-Hardness
-Density
-Cleavage/fracture
-Streak
-Lustre
-Colour
-Other diagnostic properties (crystal shape, reaction with HCl acid and twinning)
What is hardness and how can it be tested?
Hardness is the resistance of a mineral to scratching. It can be tested by Moh’s scale which chooses ten common reference minerals. Fingernails (2.5), copper coins (3.5), steel blade (5.5) and glass (7).
What is density and how can it be tested?
Density is the mass per volume and is dependant on chemical composition and crystal habit. Density can be calculated by mass/volume or displacement of water. Hefting can also be used to approximate which mineral is denser.
What is colour?
Reflects the chemical composition of a mineral. Felsic=light mineral and mafic=dark mineral.
What is lustre?
The reflective properties of a mineral. Varies from dull to resinous+silky to bright.
What is streak?
The colour left when a mineral is scratched across a pottery tile.
What is cleavage?
The tendency for a mineral to break along flat surfaces. Weak bonds results in the mineral splitting along planes. A mineral that is strongly bonded may have no cleavage. Assessed as perfect, good or poor.
What is fracture?
The tendency for a mineral to break along irregular surfaces other than cleavage planes. All minerals show fracture either along cleavage planes or in minerals in any direction.
What is crystal habit+form?
This is the shapes of minerals. Well-formed=euhedral crystals and poorly-formed=anhedral crystals.
What is reaction to HCl acid?
Whether the mineral fizzes or not. Calcite will react violently and fizzes as CO2 is likely to escape.
What is a rock?
A naturally occurring aggregate of one or more minerals.
Define an igneous rock.
A rock that has cooled (crystallised) from molten material (magma), either on the Earth’s surface after an eruption/beneath the surface.
Define a sedimentary rock.
A rock that has formed from fragments of other rocks neither from the weathering or erosion of pre-existing rocks at the surface. Lots of rock and mineral/sediment particles are later deposited onto surrounding surfaces/oceans. Upon burial beneath more sediment, deposits become hard (consolidated) and a sedimentary rock is formed.
Define a metamorphic rock.
A rock that has been altered and recrystalised by heat/pressure at depth.
What are the observations of an igneous rock?
-Crystalline texture
-Interlocking crystals=randomly orientated
-Hard, compact rock
What is the mode of origin of an igneous rock?
Crystals/minerals must have grown together during cooling and crystallisation from a magma.
What are the observations of a sedimentary rock?
-Particles of rock as well as individual mineral grains
-Gaps left between minerals
-Fragmental texture
-Soft (friable) rock
What is the mode of origin of a sedimentary rock?
Particles and fragments indicate this was once a sediment that has become consolidated (hardened) to form a rock.
What are the observations of a metamorphic rock?
-Crystals visible which are interlocking
-Crystalline texture
-Individual crystals within the rock are aligned in one direction
-Hard rock
What is the mode of origin of a metamorphic rock?
The crystals are not formed from a liquid source (magma) but are the result of recrystallisation or reorientation of earlier minerals in a pre-existing rock under conditions of intense, directed pressure.
What is texture?
The physical relationships between particles from which a rock is made.
What is crystalline texture?
Minerals have grown together as groupings of crystals that are interlocking.
What is fragmental texture?
Individual minerals/grains/rock particles are not grown together, they are transported and deposited further together later.
Give the stages of the rock cycle in order.
1.Weathering
2.Erosion
3.Transportation
4.Deposition
5.Lithification
Sedimentary rocks form
6.Heat/pressure
Metamorphic rocks form
7.Melting
Magma
8.Cooling/crystallisation
Igneous rocks form
What are the two eons?
Cryptozoic (hidden life) and Phanerozoic (visible life).
What are the eras oldest to youngest?
-Palaeozoic (old life)
-Mesozoic (middle life)
-Cenozoic (new life)
What are the periods oldest to youngest?
-Pre-cambrian
-Cambrian
-Ordovician
-Silurian
-Devonian
-Carboniferous
-Permian
-Triassic
-Jurassic
-Cretaceous
-Tertiary
-Quaternary
What is the difference between a law and a principle?
A law is something that is always true and a principle is something that is mostly true, however there can be exceptions.
What is the principle of superposition?
In a sequence of rocks, the rocks at the base are the oldest and those at the top are the youngest. This can be untrue if the rocks have been upturned by tectonic activity.
What is the law of included fragments?
Fragments eroded from and older rock can be found within younger rocks. The fragments have to be older than the rock that they are found in.
What is the law of cross cutting relationships?
Features which cut through rocks must be younger than the rocks they cut.
What is the principle of original horizontality?
Most sedimentary rocks are laid down horizontally under marine conditions. If the rocks are tilted, then they must are assumed to have been moved by tectonic forces.
What is the principle of lateral continuity?
Layers of sediment initially extend laterally in all directions. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
How are folds and faults formed?
Folds are formed after the rocks have been laid down due to compressive forces causing crustal shortening. Faults are formed after the rocks have been formed by either tensional, compressional or sheer forces.
What are unconformities and how are they formed?
Gaps in the geological record where there is no sediment being deposited or preserved.
Formed when older rocks are folded, faulted, uplifted or eroded before more deposition occurs.
What is absolute/ radiometric dating?
Gives the date of geological materials and events as an age in years before present.
How is the method used?
Based on the rate of decay of radioactive isotopes.
What do radioactive parent isotopes do?
Spontaneously emit protons and neutrons and decay into daughter isotopes.
What is half life?
The amount of time needed for half the parent isotope to decay to a daughter isotope.
What happens during alpha decay?
2 neutrons and 2 protons are lost.
What happens during beta decay?
Neutron loses an electron and becomes a proton.
What happens during electron capture?
A proton captures an electron and becomes a neutron.
If there are 1000 parent atoms in a sample, how many will there be after 1,2 and 3 half lives?
1=500 parent and 500 daughter
2=250 parent and 750 daughter
3=125 parent and 875 daughter
Why are radiometric ages always considered to be minimum ages?
Some daughter atoms may have escaped early on.
What are the three radiometric dating types and what are their approximate half lives?
Rubidium and strontium= 50 Ga
Uranium and lead= 7.13 Ma
Carbon and nitrogen (carbon dating)= 6 Ka
What is carbon 14 dating?
Compares the ratio of C14 isotopes to the ratio of C13 and C12 isotopes.
What is the rock cycle?
A set of processes by which earths materials change overtime.
What are the energy inputs to the rock cycle?
External/solar energy (surface processes) and internal/geothermal energy (internal processes).
What is the average thickness, composition and density of an oceanic crust?
-7km
-basaltic
-3.0g/cm3
What is the average thickness, composition and density of a continental crust?
-35km
-granitic
-2.7g/cm3
At constructive plate boundaries:
Where does the magma come from?
Direction of plate movement?
Types of crust involved?
Oceans become narrower or wider?
Example?
-The partial melting of the peridotite mantle
-Away from each other
-Two oceanic plates
-Wider
-Southern Iceland
At constructive plate boundaries-rift valleys:
Where does the magma come from?
Direction of plate movement?
Types of crust involved?
Oceans are created or destroyed?
Example?
-The partial melting of the peridotite mantle
-Away from each other
-Two continental plates
-Created
-Great African/East African Rift Valley
Where does the magma come from?
Direction of plate movement?
Types of crust involved?
Oceans are created or destroyed?
Example?
-Hydration melting of the subjecting plate
-Towards each other
-Oceanic and continental or two oceanic
-Destroyed
-South America
What is the region of an earthquake foci called?
A Benioff Zone.
What happens at destructive plate boundaries?
Magma forms by partial melting. The denser plate is subducted, earthquakes are produced. The magma rises forming volcanoes at the surface. These volcanoes are islands in a chain called an island arc. An example of this would be Japan.
At convergent (continental collision) boundaries:
Where does the magma come from?
Direction of plate movement?
Types of crust involved?
Why does subduction not occur with continental crust?
Example?
-The base of the continental crust
-Towards each other
-Two continental plates
-Both the same density
-The Himalayas
At conservative plate boundaries:
Is there any volcanic activity here? Why (not)?
Direction of plate movement?
Types of crust involved?
Example?
-No, there is no magma being generated
-Opposite directions/same direction
-Any
-San Andreas Fault, California
What evidence can we use to show that two continents were previously joined?
-Fossils
-Matching mountain chains
-Similar rock sequences
-Glacial deposits
What are the properties of quartz (silicate)?
-Hardness 7, not scratched by steel
-No cleavage, but shows conchoidal fracture
-Hexagonal crystals terminated by pyramids
What are the properties of orthoclase feldspar (silicate)?
-Hardness 6, barely scratched by steel
-2 cleavages intersecting at 90 degrees results in blocky shape
-Commonly flesh coloured or a pinkish-white
-Crystals show simple twinning, where the crystals grow in pairs
What are the properties of plagioclase feldspar (silicate)?
-Hardness 6, barely scratched by steel
-2 sets of cleavages intersecting at 90 degrees resulting in blocky form
-Commonly creamy white or grey in colour
-Crystals show multiple or repeated twins
What are the properties of biotite mica (silicate)?
-Hardness 2.5-3.0 scratched by a copper coin
-Shows perfect basal (parallel) cleavage
-Has a distinct pearly lustre
-Brown or black in colour
What are the properties of muscovite mica (silicate)?
-Hardness 2.5-3.0 scratched by a copper coin
-Shows perfect basal (parallel) cleavage
-Has a distinct pearly lustre
-Whitish, straw or silvery in colour
What are the properties of hornblende (amphibole /silicate)?
-Hardness 5.0-6.0, sometimes or only just scratched by steel
-2 sets of cleavages intersecting at 60 degrees/120 degrees
-Greenish black in colour
What are the properties of augite (pyroxene/silicate)?
-Hardness 5.0-6.0, just scratched by steel
-2 sets of cleavages intersecting at 90 degrees
-Greenish black in colour
What are the properties of olivine (silicate)?
-Hardness 6.0-7.0, not scratched by steel
-Olive green in colour
-No cleavage
What are the properties of andalusite/chiastolite (silicate)?
-Hardness 6.5-7.5, not scratched by steel
-Occurs as needle-like crystals but square in cross-section
-Crystals have dark inclusions in the centre, like lead in a pencil
What are the properties of garnet (silicate)?
-Hardness 6.5-7.5, not scratched by steel
-Rhombdodecahedral crystal form, 12 faces each one a rhombus
-No cleavage
-Red/brown or green in colour
What are the properties of calcite (carbonate)?
-Hardness 3, just scratched by a copper coin
-Perfect rhombohedral cleavage, 3 planes intersect at 60 degrees/120 degrees to give cleavage rhombs
-Effervesces and gives off carbon dioxide when dilute hydrochloric acid is applied
What are the properties of fluorite (halide)?
-Hardness 4, scratched easily by steel but not by a copper coin
-Perfect octahedral cleavage, cubic crystals have the corners missing at a 45 degree angle
-Fluoresces in ultra violet light
-Commonly purple, green or yellow in colour
What are the properties of halite (halide)?
-Commonly known as rock salt
-Hardness 2.0-2.5, scratched by a fingernail
-Perfect cubic cleavage, 3 planes intersecting at 90 degrees
-Tastes salty when put on the tongue
What are the properties of gypsum (sulphate)?
-Hardness 1.5-2.0, easily scratched by a fingernail
-Perfectly basal (parallel) cleavage
-Often fibrous in appearance (satin spar)
-Arrow head/fish tail twinned crystals common
What are the properties of barytes/barite (sulphate)?
-Hardness 3.0-3.5, barely scratched by a copper coin
-Dense for a non-metallic mineral (4.5)
-Often shows perfect basal (parallel) cleavage, occasionally displays 2 cleavages
-Commonly shows bladed crystal
What are the properties of chalcopyrite (sulphide)?
-Hardness 4, not scratched by a copper coin
-Black streak with gold strands within it, overall greenish gold colour
-Metallic lustre
-Tarnishes to peacock colours
What are the properties of pyrite (sulphide)?
-Also known as “fools gold”
-Greenish black streak
-Hardness 6.0, barely scratched with steel
-Metallic lustre
-Brassy gold colour
-Cubic crystals show striated faces
-Strikes fire (sparks) with steel
What are the properties of galena (sulphide)?
-Perfect cubic cleavage, 3 planes intersect at 90 degrees
-Hardness 2.5, easily scratched by a copper coin
-Lead grey streak
-Very dense (7.5)
What are the properties of hematite (oxide)?
-Hardness 5.5-6.5, barely scratched by steel
-Cherry red streak
-Metallic lustre
-Often occurs as kidney shaped masses with a fibrous internal structure
What are oxides and give an example?
Minerals comprising atoms of oxygen plus other metal atoms and an example is haematite-iron oxide (Fe2O3).
What are sulphides and give an example?
Minerals comprising atoms of sulphur plus other metal atoms and an example is galena-lead sulphide (PbS).
What are halides and give an example?
Minerals comprising halogens (chlorine, fluorine) and other metal atoms and an example is fluorite-calcium fluoride (CaF2).
What are carbonates and give an example?
Minerals comprising carbon and oxygen atoms plus other metal atoms and an example is calcite-calcium carbonate (CaCO3).
What are sulphates and give an example?
Minerals comprising sulphur and oxygen atoms plus other metal atoms and an example is barytes-barium sulphate (BaSO4).
What are silicates and give an example?
Minerals comprising silicon and oxygen atoms plus other metal atoms and an example is quartz (SiO2).
What is a compound?
Minerals composed of two or more different types of atoms which are chemically bonded together.
What are the feldspars?
Comprise of two main groups orthoclase (alkali) feldspars-rich in Na and/or K and plagioclase feldspars-rich in Na and/or Ca.
What are the ferro-magnesian minerals?
A group of silicate minerals rich in iron and magnesium and an example is biotite mica.
What are the clay minerals?
Produced by the chemical alteration and decomposition of primer silicate minerals (except quartz) and an example is olivine breaking down in serpentine.
