Topic 2 - Rocks - Recycling The Planet Flashcards
What is the diameter of the earth in km?
12 742 km
How thick is the atmosphere around Earth in km?
100 km
How long ago was the earth created?
4.6 billion years ago
What are the 3 types of rock varieties?
Igneous
Metamorphic
Sedimentary
How are igneous rocks formed?
By cooling and solicitation of molten liquid rock
How are metamorphic rocks formed?
By recrystallisation of pre-existing rock as a result of changes in pressure and temperature
How are sedimentary rocks formed?
By the accumulation and burial of layers of rock debris
By lithification of materials that were originally weathered from pre existing rocks
What is the definition of ‘mineral’?
In everyday language it can mean:
Anything that is neither an animal nor a plant
Certain chemical components of food
In earth science it means:
A mineral is a solid material, formed by natural processes, with a chemical composition that falls within certain narrow limits and with its constituents atoms arranged in a specific regular ,three dimensional array or pattern.
Is mineral water a mineral?
Mineral water is not a mineral because it is not solid. It is named this way because the water contains a small amount of dissolved material derived from having been in contact with soluble minerals underground.
How many different minerals are there?
Almost 4000 and new ones are being discovered every year
What is a crystal?
It is a closely related term to mineral, which describes a solid material whose atoms are arranged in a specific, ordered arrangement. This arrangement gives rise to the material having flat faces arranged in a particular orientation and hence he characteristic geometrical shape such as a cube or octahedron.
How can different minerals vary in terms of their composition and or atomic structure and display contrasting physical properties and appearances as a result. How can they be differentiated?
Colour
Lustre
Form or shape
What is the lustre of a mineral?
The appearance caused by how light is reflected from the minerals surface for example, metallic, glassy(or vitreous) or dull
How can the form and shape of a mineral affect a mineral?
Crystal form often mimics atomic structure
Crystals are much longer than they are wide are said to have a prismatic form
Crystals that are flat are said to be tabular
Crystals with square faces intersecting at 90 degrees are cubic
Crystals with six equal sided faces that don’t intersect at 90 degrees are rhombohedral
What other properties can be used to classify and identify minerals other than colour, lustre or form?
Density
Hardness
The pattern on a fractured broken surface
How is density measured in minerals?
Grams per cubic centimetre
Kilograms per cubic metre
What is the hardness of a mineral influenced by?
The atomic structure
What is a conchoidal fracture?
A fracture that looks like concentric bands seen on some shells such as mussels.
Describe what the mineral property ‘cleavage’ is ?
The tendency for a mineral to break apart along preferred planes of natural weakness in its crystal structure.
Why does cleavage of a rock occur?
It is a consequence of the way the constituent atoms are arranged.
Which mineral shows the property cleavage very clearly? And how is it arranged.
Mica
It’s atoms are arranged in layers or sheets , so crystals of mica tend to split apart parallel to the sheets like the pages of a book. Mica has just one set of cleavage surfaces parallel to each other, so this is why mica forms platy or flake like crystals.
What is the chemical composition of amphibole?
Iron Magnesium Calcium Aluminium Silicate containing water
What is the crystal form and colour of amphibole?
Black and elongate
What is the cleavage of amphibole?
2 sets of cleavage
Planes intersecting at about 120 degrees when crystals viewed end on
What is the chemical composition of calcite?
CaCo3
What is he colour of calcite?
White
How many sets of cleavage does calcite have?
3
What does calcite react with and what does it produce?
Acid
It produces Co2 gas
What is the chemical composition of feldspar?
Occurs as two types
Potassium-aluminium-silicate
(Potassium feldspar variety)
Sodium - calcium- aluminium- silicate (plagioclase feldspar variety)
What is the crystal form of feldspar?
Prismatic, tabular
What colour does feldspar appear?
White and pink
What is the chemical composition of Garnet?
Iron Magnesium Calcium Aluminium Silicate
What is the colour of garnet?
Red- brown
What is the crystal form of garnet?
Equidimensional, 12 sided (dodecahedral)
What is the chemical composition of Halite?
NaCl (sodium chloride)
What is the crystal form of halite?
Cubic
What is the colour of Halite?
White
What is the chemical composition of kyanite?
Aluminium silicate
What is the lustre of kyanite?
Glassy
What is the crystal form of kyanite?
Prismatic, bladed
What what is the chemical composition of Mica?
Potassium Magnesium Iron Aluminium Silicate Contains water (Dark mica)
Potassium Aluminium Silicate Contains water (White mica; muscovite)
What is the lustre of mica?
Glassy
What is the crystal form of Mica?
Tabular, Platy
What is the chemical composition of quartz?
Silicon dioxide
What is the lustre of quartz?
Glassy
What is the crystal form of quartz?
Prismatic
What are silicate minerals?
Minerals containing silicon and oxygen
What are ore minerals?
Ores are naturally occurring rocks that contain metal or metal compounds in sufficient amounts to make it worthwhile extracting them. The method used to extract a given metal from its ore depends upon the reactivity of the metal and so how stable the ore is. The uses of metals depend on their properties. Alloys are made by mixing a metal with another material in order to improve the properties.
No silicate
What is the scientific definition of the term ‘rock’?
Any naturally formed, solid assemblage of mineral grains is defined as a rock and may consist of on type or mineral but island several minerals
How do igneous rocks form?
When molten (liquid) rock material called magma cools down and solidifies.
What is magma?
Molten (liquid) rock
Lava
Where does the word igneous come from?
It comes from the Latin word ignis meaning fire.
What two categories does igneous rock fall in to?
Extrusive igneous rocks
Intrusive igneous rock
Describe what extrusive igneous rocks are and where they form?
Rocks that form by the extrusion (forcing out) of magma onto the Earths surface at volcanoes.
Which Igneous rock category does ‘Lava’ fall in to?
Extrusive igneous rocks
Describe what intrusive igneous rocks are and how they are formed?
Intrusive igneous rocks form deep underground, as the magmas were forced into (intruded) pre existing rocks.
What is a pluton?
It is an igneous rock that has forced into pre existing rocks
It is an intrusion can be several kilometres across known as a pluton while others are no more than a few metres
What is a narrow slab shaped intrusion of igneous rock that stands vertically called?
A dyke
What is an intrusion called that long narrow slab shaped intrusion that lies horizontally?
A sill
What happens to magma as the temperature falls by a small amount?
Particular minerals start to appear as microscopic nuclei (or seeds)
What is crystal nucleations?
This is when particular minerals start to appear as microscopic crystal nuclei or seeds as the temperature of a solution cools
What happens when magma cools further for a longer period of time in terms of crystal nucleation?
On further cooling the crystals grow even larger and new minerals start to nucleate and then grow. Eventually, there are enough crystals to form an interlocking network. After a little more cooling the last crystals to grow full spaces between and the magma has become a completely solid igneous rock.
Define what is meant by the ‘texture’ of a rock?
The shape of the grains, their size and relationship between them define texture
It is a mixture of randomly oriented crystals of different minerals forming an interlocking network because this is the way the crystals nucleated and grew from a cooling liquid. It is an important distinctive feature of igneous rocks
What effect does the rate of cooling have on rock?
The rate at which magma cools has a significant effect on the texture of the resulting rock
What effect does slow cooling of rock have on the nuclei?
In general, slow cooling allows a relatively small number of nuclei to form, which then gradually grow into large crystals
What effect does fast cooling of rock have on the nuclei?
Very fast cooling causes crystallisation to occur by the nucleation of small crystals rather than the steady growth of a few crystals
Which rate of cooling of igneous rock results in fine grains?
Fast cooling
What rate of cooling of igneous rock results in larger grains?
Slow cooling
What can happen in extreme cases when crystal nucleation is inhibited?
The liquid solidifies very quickly as a crystal free volcanic glass
What is partial melting?
It is when a rock will melt over a range of temperatures within which crystals and liquid coexist (the reverse of crystallisation)
How are metamorphic rocks formed?
They form from pre existing rocks when one set of minerals transforms into another. This happens when the pressure or temperature that they are subjected to changes, but without any melting taking place. In other words metamorphic rocks form in the solid state.
What happens to any rock when it is subjected to sufficiently high temperature and/or pressure?
The atoms in minerals making up the rock become reorganised, even when conditions are not hot enough to cause melting. pre existing crystals of a given mineral may regrow to form new crystals of the same mineral, or crystals of different minerals may react with each other to produce new minerals. Either way, we re-crystallisation takes place in the solid state the new rock is known as a metamorphic rock
What is a foliation in a rock?
The alignment of platy minerals means that there are closet spaced planes of weakness running through the rock. These weaknesses mean that the rock tends to split apart into fairly flat pieces. The rock is said to have foliation because its mineral grains are aligned like a stack of leaves (foliage) lying on top of each other.
What type of rock is slate?
A metamorphic rock
What is contact metamorphism?
It is metamorphism in the rock surrounding the magma which has been caused by heating, so this is known as thermal metamorphism or contact metamorphism and is confined to the area no more than about a kilometre or so from the contact
What does the end product of metamorphism depend on?
The chemical composition of the starting rock
The pressure
Temperature
In which 3 ways does sedimentary rock form?
The accumulation and burial of layers of rock debris
The growth of organically produced rock structures such as coral reefs
The accumulation of salty mineral deposits where seawater evaporates
What are layers of sedimentary rock called?
Beds or strata
What is the starting point in the formation of sedimentary rocks?
It occurs at the earths surface where rocks are slowly broken up by exposure to rain, wind and frost. This process is known as weathering.
What is erosion?
It is when small rock particles and grains crumble away from the bulk rock and can be picked up and removed by flowing water, wind or glaciers
What is erosion usually followed by?
By the processes sediment transport and then deposition eventually resulting in roughly horizontal layers of sediment being laid down
What is lithification?
It is when accumulated layers of sediment become compacted under the weight of overlying sediment and new minerals may grow in the spaces between grains. In this way, loose sedimentary grains become cemented together forming a solid sedimentary rock
What type of rocks usually have a fragmental texture?
Sedimentary rock
What is a fossil?
It is defined as any evidence of ancient life that has become naturally preserved within a rock for example ammonites
Give two ways in which sedimentary processes differ fundamentally from both igneous and metamorphic processes?
First sedimentary processes happen at the earths surface (land surface and in the oceans) whereas igneous and metamorphic processes happen well below the surface. An exception to this is with extrusive (volcanic) igneous rocks, but even these require subsurface processes to feed them
Second igneous and metamorphic processes happen at high temperatures and pressures, whereas sedimentary processes occur at normal surface temperatures
What are the two types of weathering?
Physical
Chemical
What is physical weathering?
This is where it directly breaks rocks in to fragments and several processes cause this. E.g. Water expands slightly as it freezes. When this happens in a confined space, such as a crack within a rock, pressure builds up and breaks the rocks apart.
Heating and cooling also produce forces within rocks l. Solar radiation can heat rock to uncomfortable temperatures even in areas such as Antarctica
Which property of minerals is likely to assist breakage?
Some minerals have one or more cleavage planes. The planes of weakness within their crystal structure that allow them to break apart more easily
Easily cleaved minerals have one or more cleavage planes - the planes of weakness within their crystal structure allow them to break apart more easily
What is chemical weathering “?
It occurs on rock surfaces that are exposed to naturally acidic rainwater and stronger acids produced by vegetation (particularly when vegetation decays in the soils of the humid tropics)
What does the chemical decomposition of minerals generally result in?
Dissolved material that gets carried away in surface water and rivers
New residual solid minerals
Give a common example of a rock that can react to acid rain?
A common example is the chemical decomposition of feldspar, which you’ll recall is a silicate mineral containing sodium, calcium, potassium and aluminium. When it reacts with weak acid, the products are tiny crystals of clay (an insoluble mineral) and ‘salty’ water containing the most soluble components of the original feldspar. We can write this as:
Feldspar + weakly acid rain or soil > clay and dissolved salts
What can rock be exposed to to cause erosion?
Flowing water, wind, frigid conditions, a glacier, pebbles, sand grains, strong winds and fragments jutting from the Ade of a moving glacier can pound, blast and scrape more debris to wear away the surfaces over which they pass.
As well as grain size which of the following properties of mineral grains are likely to play a role in determining whether grains will be picked up and eroded away?
Grains with high density are heavier than low density grains of the same size, so will be harder to dislodge and pick up. Hardness and lustre will not play a role
Suggest two conditions in which there will be no selective erosion of given grain sizes?
Under extremely slow flow speeds not even the smallest grain sizes will be eroded, and under extremely high flow speeds, grains of all sizes will be eroded
What is a suspended load?
It is when small sedimentary grains can be carried in suspension. For example clay and silt in flowing water
What grains move by a process called saltation?
Larger grains may bounce along the river or seabed in a process called saltation.
From Latin saltare ‘ to leap or jump’
What is a dissolved load?
The water itself carries the soluble material produced during chemical weathering
What kind of grain is produced from a longer history of erosion, transport and deposition?
A narrow range of grain sizes
What is meant by the sorting of sediment?
A sediment with a wide range of grain sizes is said to be poorly sorted
A well sorted sediment has a narrow range of grain sizes, and results from extensive reworking of a sediment by wind action in deserts, or wave action on beaches and in shallow seas
What is sedimentary bedform?
It is a general term for any three dimensional structure formed on a surface where sediment is being deposited or eroded.
The local environmental conditions will determine the type and size of the bedforms, such as ripples on a sandy beach or sand dunes in a desert or the patterns of cracks on a friend out mudflat
What are evaporites?
Sedimentary rocks that are not fragmentary in texture but are made of intergrown crystals. They are usually distinguishable as sedimentary deposits by their layering and are often associated with other sediments formed in arid environments.
How do marine organisms in seawater produce shells and skeletons?
Many groups of organisms take up some calcium and carbon dioxide (CO2) that is dissolved in seawater to produce shells or skeletons composed of calcium carbonate (calcite)
What is limestone made of?
Depending on environmental conditions some marine settings with marine organisms that have shells and skeletons made from the calcium carbonate in water over huge periods of time accumulate on the sea floor and become solid rock called limestone.
What is lithification?
A process by a combination of compaction under the weight of overlying sediment and cementation
What is cementation?
It is a process that involves new mineral growth between sediment grains and analogous to what happens in a bowl of damp sugar grains
The wet grains dissolved slightly in the water and the sugary solution coats the grains. When the water evaporates, the gaps between the crystals are filled by newly crystallised sugar, binding the crystals into a hard lump
What two consequences does chemical weathering have?
It releases material into solution and can produce new minerals from old, such as clay from feldspar
What kind of flow rate does erosion require? What is needed for deposition?
Erosion requires sufficiently fast flow rates. When flow speed slacken below a certain threshold (which is lower than the threshold for erosion to take place grains are deposited
What is a good starting point in working out he environment in which rocks were formed?
To examine their texture
What is petrology?
The study of rocks and their constituents
What is granite ??
It is a course grained (average grain >2 mm) and is composed mainly of feldspars and quartz, with minor amounts of Mica and or amphibole
What is gabbro?
It is a course trained and composed mainly of calcium rich plagioclase feldspar and pyroxene, possibly with minor amounts of olivine
What is basalt?
A fine grained (average size <1mm) and is composed mainly of calcium rich plagioclase feldspar and pyroxene, possibly with minor amounts of olivine
What is fractional crystallisation?
It is when a new liquid (rock) becomes separated from the crystals, say if minerals sink out of the liquid, then new liquid magma with a different chemical composition from the initial liquid is available. It is important because it produces a range of magma compositions and hence a range of igneous rock compositions.
