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Geology > Geological Materials > Flashcards

Geological Materials Flashcards

1
Q

Rock

A

Any formation of natural origin in the earth, composed of a single mineral, or an aggregate of a number of minerals.

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2
Q

Mineral

A

Naturally occurring, inorganic, solid compound or element, with a definite chemical composition and a regular internal structure composed of repeating bonded atoms or molecules. Crystalline.

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3
Q

Igneous

A

Crystallised from magma which is produced by partial melting of rocks at depths typically down to 150km.

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4
Q

Sedimentary.

A

Mostly formed from the products of weathering of rocks exposed at the earths surfaces which have been deposited by (or in) water, wind or ice, buried the lithified.

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5
Q

Metamorphic

A

Formed by the transformation of pre-existing rocks in the solid state by the influence of changing pressures and temperatures.

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6
Q

Texture of minerals

A

Way the minerals in a rock exist together:
Interlocking grown together from magma - CRYSTALLINE
Broken fragments/grains of weathered/eroded rocks - CLASTIC

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7
Q

SiO2

A

Quartz

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8
Q

Al(2)O(3)

A

Corundum

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9
Q

Fe(2)O(3)

A

Haematite

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10
Q

CaCO(3)

A

Calcite

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11
Q

Mg(2)SiO(4)

A

Olivine

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12
Q

Crystalline

A

Minerals are arranged in an orderly, repeating, 3D Array

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13
Q

Glass

A

Absence of mineral formation

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14
Q

Anions

A

Negative charge (extra electrons)

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15
Q

Cations

A

Positive charge (loss of electrons)

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16
Q

Habit

A

The development of an individual crystal, or aggregate of crystals, to produce a particular external shape, with development depending on the conditions obtaining during formation.

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17
Q

Prismatic

A

Means that mineral has an elongated habit with the bounding faced forming a prismlike shape, as is common in members of the pyroxene and amphibole groups of silicates.

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18
Q

Columnar

A

Exhibits rounded columns as is common in tourmaline.

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19
Q

Acicular

A

Means needlelike (zeolite).

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20
Q

Tabular

A

Describes crystal masses that are flat like a board as commonly seen in barite.

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21
Q

Fibrous

A

Refers to threadlike masses, as exhibited by chrysotile, the most common mineral included in the commercial term asbestos.

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22
Q

Massive

A

Describes a mineral specimen that is totally devoid of crystal faces.

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23
Q

Cleavage

A

Crystals split along planes of weakness inherent in the structure of their atomic lattices.
Set fractures closely spaced.

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24
Q

Planar cleavage

A

Cleavage along a single planar direction. MICA minerals.

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25
Q

Prismatic cleavage

A

Two different cleavage directions whose lines of intersection are commonly parallel to a specific crystallographic direction.

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26
Q

Cubic cleavage

A

Mineral fragments that have cubic outlines on account of three cleavage directions at 90 degrees to one another.

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27
Q

Rhombohedral cleavage

A

Results in fragments with an external shape with six sides. Carbonates and calcite.

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28
Q

Conchoidal fracture

A

Curvature of the interior surface of a shell. Same as in glass due to absence of clearly defined planes of weakness in the crystal structure of quartz or glass.

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29
Q

KAlSi(3)O(8)

A

Orthoclase

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30
Q

Sheet silicates

A

Silicate minerals characterised by possessing layers of SiO(4)^(4-) to form a flat sheet with the composition Si(4)O(10). Includes micas, chlorite, clays.

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31
Q

How do crystals form? (Temp drop)

A

As a melt’s temperature drops, it gradually becomes unstable as a melt and reconfigures into ordered minerals that are more stable. Minerals CRYSTALLISE.
MAGMA COOLING

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32
Q

How do crystals form? (Ionic solution)

A

Ionic solution becomes supersaturated in ions such that crystals must precipitate out of solution.
Salt forming from seawater.

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33
Q

How do crystals form? (Change Physical/chemical conditions)

A

Change the physical or chemical conditions of an existing system ie temp or pressure. The existing crystals may not be stable at the new conditions so the ions in the solid minerals will rearrange themselves in the solid state to form new minerals which are more stable.
GRAPHITE TO DIAMOND.

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34
Q

Mineral stability depends on

A 
Temperature
Pressure
pH
Water availability,
Gas content,
Biological activity.  
Proportions of elements available - depend on environment crystallisation occurs in.
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35
Q

Mineral stability (carbon polymorph)

A

Form diamond and graphite = mineral polymorphs.
Formed in different environments - graphite is low pressure and temp
- diamond is the high pressure and temp
- ~50/60 kilobits pressure = 150 km down.

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36
Q

8 main minerals that make up 99% of crust.

A 
Oxygen,
Silicon,
Aluminium,
Iron,
Magnesium,
Calcium,
Potassium,
Sodium.
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37
Q

Silicate anion

A

Tetrahedral, most minerals on earth’s building block.
Chains or sheets.
Bond with cations.

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38
Q

Key mineral groups

A 
Silicates
Native elements
Halides
Oxides
Sulphides
Carbonates
Sulphates
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39
Q

Main silicate minerals are

A 
Olivine 
Pyroxene
Amphibole
Mica
Feldspar
Quartz
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40
Q

Example of isolated tetrahedra

A

Olivine

Garnet

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41
Q

Example of single chain silicate

A

Pyroxene

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42
Q

Example of double chain silicates

A

Amphibole

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43
Q

Example of sheets of tetrahedra silicates

A

Mica

Clay minerals

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44
Q

Examples of 3D frameworks of tetrahedra silicates

A

Quartz

Feldspar

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45
Q

Isolated tetrahedra

A

Each silicate tetrahedra exists on its own, it does not share oxygens with any other silicate tetrahedra.
Net charge remains as 4-
Tetrahedra bonded by cations that satisfy the negative charge. 2 divalent cations (Mg2+,Fe2+)
OLIVINE

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46
Q

Silicate tetrahedra chemical symbol

A

SiO(4)

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47
Q

Olivine mineral group

A

(Mg.Fe)(2)SiO(4)-isomorphic substitution
Any proportion or Mg and Fe
Solid solution!
No shared oxygens between tetrahedra only weak ionic bonds.
No regular repeating planes of weakness
Fractures in an irregular fashion - no cleavage.
Hardness 6-7
Conchoidal fracture.

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48
Q

Solid solution

A

Solid crystalline phases representing a mixture of two or more end members which may vary in composition within finite limits without the appearance of a another phase.

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49
Q

Single chain silicate basic formula

A

[SiO(3)]2-

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50
Q

Single chains ORTHO-PYROXENE formula

A

(Mg,Fe)SiO(3) Or (Mg,Fe)(2)Si(2)O(6)

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51
Q

Single chain CLINO-PYROXENE formula

A

Ca(Mg,Fe)Si(2)O(6)

52
Q

PYROXENE

A

Black, hard to tell difference between ortho and Clint pyroxene.
2 perfect cleavages at 90 degrees
Strong Si-O and O-O bonds

53
Q

Double chain silicates AMPHIBOLE

A

[Si(8)O(22)]12-
With an OH- is hydrated
Charge is balanced by variety of cations.
Hornblende is most frequent and black

54
Q

Hornblende amphibole

A

Black or green

Two prominent cleavages at 60/120 degrees

55
Q

Sheet silicate MICAS

A

[Si(4)O(10)]4-
Two sheets linked octahedrally
Flakey

56
Q

Framework silicates QUARTZ

A 
SiO(2)
Pale coloured or transparent. 
Chemically indestructible 
No cleavage
7 on Mohs scale. 
Conchoidal fracture.
57
Q

Framework silicates FELDSPAR

A

XAl(Si(2)O(8)

Potassium=orthoclase feldspar
Prismatic cleavage. (ALKALI FELDSPAR)

Plagioclase feldspar - Na to Ca

58
Q

Key mineral properties

A 
Colour
Lustre
Streak
Hardness
Crystal habit
Cleavage 
Fracture
59
Q

Microcline twinning

A

Really really slow cooling of orthoclase. corsshatched.

60
Q

Magmas form from

A

Partial melts of mantle or crust through decompression melting or hydration melting. Pressure and volatiles influence temp.

61
Q

Magna generation is linked to

A

Plate tectonics

62
Q

Partial melt of mantle produces a _____ magma

A

Mafic

63
Q

Magmatic differentiation.

A

How we get intermediate and silicic felsic magmas and rocks

64
Q

3 main processes of magmatic differentiation

A

Fractional crystallisation
Assimilation/contamination
Magma mixing/ replenishment

65
Q

Bowen’s reaction series

A

The evolution of magma is linked to the specific order of crystallisation of the silicate minerals
Fixed order in which the silicate minerals crystallise.

66
Q

3 key groups of Bowen’s reaction series

A

Discontinuous reaction series of mafic minerals
Continuous reaction series of plagioclase feldspars
Final crystallisation of felsic minerals

67
Q

Discontinuous series of mafic minerals

A

Mafic minerals rich in Mg and Fe (olivine pyroxene amphibole biotite) crystallise at specific temp intervals only with each new mineral adopting an increasingly more polymerised and complex silicate structure as temp descends -
isolated tetrahedra>single chains>double chains>sheets

68
Q

Mafic minerals rich in Mg and Fe

A

Olivine
Pyroxene
Amphibole
Biotite

69
Q

Continuous reaction series of plagioclase feldspar

A

Crystallises at high temp in parallel with mafic series.
Ca rich anothites and becomes more Na rich Albite Down temp. Series is continuous as mineral structure doesn’t change only Ca:Na ratio changes

Remaining felsic minerals crystallise together at lowest temps (orthoclase quartz and muscovite)

70
Q

Bowen’s reaction series is a model :

A

Doesn’t predict mafic melt with result in a rock with all silicate minerals but some.

71
Q

Bowen reaction series depends on temp and one key condition:

A

That the minerals crystallising do not react back with the magma but are effectively removed from the system as crystallisation proceeds.

72
Q

FRACTIONAL CRYSTALLISATION

A

Process by which the composition of a magma can change or evolve due to successive batches of crystals being removed from the magma.

73
Q

How does fractional crystallisation happen?

A

Different crystals form at different temps
Crystals forming remove specific proportions of elements from the magma.
Crystals forming early tend to be more dense than the magma
The denser minerals sink to the bottom of the magma chamber effectively removing them from the residual magma….
The composition of remaining magma is now different to what it was at start so had differentiated or evolved.

74
Q

Fractional crystallisation with Bowen’s reaction series

A

Olivine plagioclase And pyroxene are forming in a mafic magma and left there they will react with magma continuously so final rock will be a mafic igneous rock containing those three minerals.
REMOVE minerals so cannot react the residual magma composition will be changed.
New magma will be of a composition that is only able to crystallise minerals of intermediate composition.
AMPHIBOLE BIOTIT AND NA RICH PLAGIOCLASE

75
Q

Bowen’s reaction series predicts that fractional crystallisation. If more mafic magmas can lead to more felsic acidic silicic magmas as long as …..

A

fractions of crystals are removed from the melt!

76
Q

Other ways of separating crystals and magma

A

Filter pressing
Convective separation
Sidewall crystallisation

77
Q

Assimilation/contamination

A

Mafic magmas are high temp and have enough heat to partially melt some crust.
Crustal rocks are felsic! Melt at lower temps than mafic magmas exist.
Felsic minerals melt first and become assimilated into mafic magma contaminating it - results in magma more enriched in felsic components.

78
Q

Where does assimilation contamination occur

A 
SUBDUCTION ZONES
Hydration melting (subduction zones) - water/volatiles are added to the mantle then the melting temp is reduced giving partial melt.  
Partially melts more felsic continental crust and operating alongside fractional crystallisation a magma that is more intermediate - acidic in composition results = volcanic mountains such as Andes.
79
Q

Examples of where assimilation happens

A

Magma chambers in deep crust
Large sills and dykes in shallow crust
In areas where mantle plumes invade the crust.

80
Q

Magma mixing / replenishment.

A

Mafic + felsic = intermediate magma
Can happen anywhere where two magmas meet (feel in crust)
Magma chambers can evolve through fractionation as we saw and become more felsic in composition but are often replenished with new magma as they are objected with plumes of new mafic magma rising from deep mantle.

81
Q

Intermediate magma facts

A 
Medium temp ~1000-900
55-65% wt% silica
Moderately viscous - resist flow
Moderate to high volatile content
Erupt effusively or explosively 
Convergent plate boundaries
ANDESITIC DIORITIC OR GRANODIORITIC MAGMAS.
82
Q

Minerals in intermediate rocks

A

Amphibole and plagioclase some biotite

A lil bit of quartz and orthoclase.

83
Q

Colour of intermediate rocks

A

Medium grey

84
Q

Fine grained intermediate rock

A

Andesite

85
Q

Medium grained intermediate rock is

A

MICRODIORITE

86
Q

Coarse grained intermediate rock

A

DIORITE

87
Q

Andesites form as

A

Lavas erupted from subduction zone volcanoes

88
Q

Diorites are formed from

A

Subduction zone magma chambers solidifying

89
Q

Microdiorites are formed from

A

Dykes and sills of intermediate magma

90
Q

Eruption style of andesites

A

Lots of volatiles = PYROCLASTIC ERUPTIONS
erupt effusively as lavas
Steep sided than mafic volcanic edifices
Caldera eruptions.

91
Q

PYROCLASTIC eruptions

A

Viscous volatile rich magmas produce PYROCLASTIC eruptions.
Depressurises and gases come out of solution - sticky magmas don’t deform for gasses release bubbles - magma froths And shatters producing TEPHRA

92
Q

Tephra

A

Tiny glassy shards of magma - Ash is larger crystalline class called lapilli and larger coasts (blocks)

93
Q

Mafic Rock

A

Igneous rock rich in magnesium and iron bearing minerals

94
Q

Basic Rock

A

Same as mafic

95
Q

Felsic Rock

A

Igneous rock rich in feldspathic minerals and silica

96
Q

Acidic rock

A

Same as felsic

97
Q

Intermediate rock igneous

A

a rock with a composition between felsic and mafic

98
Q

Ultramafic Rock

A

igneous rock that has a similar composition to the mantle, peridotite is an unltramafic rock

99
Q

2 cooling rates occur when

A

magma cools deep underground for a bit growing large crystals, then the crystals and remaining melt cam be erupted onto the surface where the rest of the magma cools rapidly to form smaller crystals

100
Q

2 cooling rates lead to

A

2 crystal sizes in rocks:

  1. Large slow cooled crystals; PHENOCRYSTS
  2. Tiny quick cooled crystals whcih crystallise last to form the rest of the rock known as GROUNDMASS (textural term)
101
Q

PORPHYRITIC TEXTURE

A

A rock with large phenocrysts and then a small groundmass

102
Q

Dikes/Dykes

A

Intrusive igneous rock formation that cuts across layers of county rock

103
Q

Sills

A

Intrusive Igneous rock that runs parallel to layers of country rock

104
Q

Type of rock formed from an Effusive eruption

A

Basic/Mafic magma

105
Q

Types of magma from a pyroclastic eruption

A

Acidic/Silicic

106
Q

Rocks formed at an ISLAND ARC PLATE SUBDUCTION

A

Mafic to Intermediate (Volcanism and plutonism)

107
Q

Rocks formed at a plate divergence

A

Basaltic extrusives and intrusives

108
Q

Rocks formed at Hot Spot Volcanism

A

Basaltic extrusives and intrusives

109
Q

Rocks formed at Continental Plate subduction

A

Mafic to felsic intrusives and extrusives

110
Q

Partial melting -

Why and where do they form?

A

minerals melt at different temps - most magmas formed from partial melts. They form at mid ocean ridges and in mantle wedges above subduction zones

111
Q

Partial melting of mantle - does the mantle always melt at same temperature?

A

doesn’t always melt at the same temperature because of pressure (melts at higher temp) and volatile content (water and gas reduce the melting temp)

112
Q

2 main processes by which the mantle partially melts

A

Decompression melting and dehydration melting

113
Q

Experiments in melting rocks tell us

A

At a given pressure a rock will melt over a range of temperatures - the melting interval. We can plot these on a graph. Point at which melting begins is the SOLIDUS
point when the rock is completely molten is the LIQUIDUS

114
Q

Solidus

A

Point on graph of melting interval where melting begins

115
Q

Liquidus

A

Point on graph of melting interval when the rock is completely molten

116
Q

Liquid produced by partial melting will be completey enriched in

A

the lowest temp components especiall Silica

117
Q

The presence of water _____ the melting temperature

A

reduces

118
Q

Rocks rich in silica melt at ____ temps than rocks poor in silica

A

LOWER

119
Q

Decompression (adiabatic) melting

A

Solid mantle, partially melts with exactly right pressures and temps at MID OCEAN RIDGES because mantle gets closest to earths surface - solid mantle flows earths surface where the crust is thinnest, it retains its heat while at lower pressures = PARTIAL MELTING
MAFIC or BASIC magma composition.

120
Q

Partial melts of the mantle

A

confining pressure drops but temp stays same and amount of partial melt can be tiny (3-5%)

121
Q

Dehydration Melting (subduction zones)

A

Water or volatiles added to the mantle, melting temp is reduced=Partial melt.
CONVERGENT PLATE BOUNDARIES-SUBDUCTION ZONES
Subducted slab contains hydrated ocean crust - at depth the water and volatiles are liberated from the slab as it heats.
Reduces melting temp of mantle wedge above the subducting slab creating a partial melt of the mantle which is a mafic basic composition of magma.

122
Q

BASIC/MAFIC MAGMAS

A

main magmas formed from partial melts in mantle.
lowest Wt% Silica of the 3 main magma types. High temps, not viscous (=runny), erupt gently - rarely explode violently like pyroclastic eruptions EFFUSIVE

123
Q

Mineralogy of Mafic Rocks

A

Pyroxene, Plagioclase feldspar, ~Olivine ~Glass

124
Q

Fine grained MAFIC ROCK

A

BASALT - lava flows on ground or at top of ocean crust

125
Q

Medium grained MAFIC ROCK

A

DOLERITE - mafic magma chambers solidifying and also form lower ocean crust

126
Q

Coarse Grained MAFIC ROCK

A

GABBRO - dykes or sills in shallow levels of crust.

127
Q

Where do we find Mafic rocks

A

OCEAN CRUST- continents rifting apart and fissure eruptions, dykes and sills, shield volcanos

Geology (4 decks)

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