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geophysics > earth materials > Flashcards

earth materials Flashcards

1
Q

define a mineral

A

minerals are naturally occuring, homogenous, crytalline solid with a definite crystalline chemical composition

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2
Q

what is continuous and constant throughout the mineral structure.

A

• Atomic structure is continuous and constant throughout the mineral structure

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3
Q

define a rock

A

•a rock is a naturally formed aggregate of mineral matter constituting a significant part of the Earth’s crust.

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4
Q

what does consolidated mean?

A

it means the rock is firm

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5
Q

what does non-consolidated mean?

A

it means the rock is loose

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6
Q

what is concrete?

A

a non-natural aggregate of other rocks set in a matrix

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7
Q

coal, limestone, evaporite. are they biogenic or inorganic?

A

coal - biogenic

limestone - biogenic

evaporite - inorganic

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8
Q

define the unit cell and what it is representative of

A

• The Unit Cell is the smallest 3D repeating unit of crystal structure,

representative of :
• atomic structure
• chemical composition
• crystal symmetry
• It has regularly ordered atoms with fixed geometry

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9
Q

what is the length of an angstrom?

A

1A = 10-10m

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10
Q

cubic = …

A

CUBIC
a = b = c; α = β = γ = 90

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11
Q

tetragonal = …

A

TETRAGONAL
a = b != c; α = β = γ = 90

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12
Q

orthorhombic = …

A

ORTHORHOMBIC
a != b != c; α = β = γ = 90

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13
Q

monoclinic = …

A

MONOCLINIC
a != b != c; α = γ = 90 β > 90

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14
Q

triclinic = …

A

TRICLINIC
a != b != c; α != β != γ != 90

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15
Q

hexagonal

A

HEXAGONAL
a = b != c; α = β = 90; γ =120

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16
Q

trigonal - rhombohedral

A

TRIGONAL - Rhombohedral
a = b = c; α = β = γ != 90 < 120

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17
Q

crystal symmetry is defined by:

A

Crystal symmetry is defined by:
• Planes of symmetry
• Axes of rotation
• Axes of inversion
All properties of a crystal substance conform to a symmetry

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18
Q

symmetry is a defining property of…

A

Symmetry is a defining property of a crystal

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19
Q

if crystal growth occurs at the same rate in all directions..

A

If this occurs at the same rate in all directions the **shape of the unit cell will be retained in the macro crystals **

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20
Q

the symmetry of the macro crystals always reflects…

A

The symmetry of the macro crystals ALWAYS reflects at least the minimum symmetry of the crystal system of the unit cell.

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21
Q

name 9 properties of minerals to aid in the identification of them

A
  • Habit of crystals and crystal aggregates
  • Density
  • Hardness
  • Cleavage
  • Colour
  • Lustre
  • Reactivity with acids
  • magnetism,
  • radioactivity
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22
Q

define habit

A

habit describes the general shape of a crystal or crystal aggregate

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23
Q

what controls crystal habit?

A

it is controlled by:

shape of the unit cell of the crystal

conditions under which the crystal formed.

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24
Q

what is nomenclature

A

they are terms to describe the form of naturally occuring minerals

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25
Q

what is the nomenclauture of this rock?

A

prismatic habit

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26
Q

what is the nomenclauture of this rock?

A

tabular habit (looks like tables on top of each other)

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27
Q

what is the nomenclauture of this mineral?

A

platy habit

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28
Q

what is the nomenclauture of this rock?

A

fibrous habit

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29
Q

what is the nomenclauture of this rock?

A

accicular habit

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30
Q

what is the nomenclauture of this rock?

A

nodular radiating habit

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31
Q

what is the nomenclauture of ths rock?

A

botryoidal habit

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32
Q

what is the nomenclauture of this rock?

A

dendritic habit

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33
Q

when does twinning occur?

A

it can occur during crystal growth, or by the deformation during the formation of the rock

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34
Q

what is twinning?

A

twinned crystals have two or more parts that are physically continuous.

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35
Q

name the three typical types of twinning found in minerals

A

simple

repeat/ polysyntheitc

interpenetrant (two cubes penetrating each other)

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36
Q

name two factors that effect density.

A

mass of the individual atoms

the packing of the atoms

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37
Q

where do fingernail, copper coin and steel knife blade come on the moh’s scale of hardness?

A

fingernail - 2.5

copper coin - 3.5

steel knife blade - 6.5

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38
Q

give the general hardness of these mineral groups

silicates

sulphides

oxides

carbonates, sulphates

A

Silicates 5 – 8
Sulphides <6
Oxides >6
Carbonates, sulphates <5

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39
Q

hardness generally increases with…

A

Hardness generally increases with density
Calcite CaCO3 D = 2.71 g/ml H = 3
Aragonite CaCO3 D = 2.93 g/ml H = 4

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40
Q

what is mineral cleavage?

A

mineral cleavage is the ability of minerals to split along well defined planes of weakness

cleavage planes represent planes of relative bond weakness in the crystal structure (distinct from rock cleavage)

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41
Q

whats the difference between cleavage and fracture?

A

fracture leaves an irregular pattern

fracture surfaces are uneven and not parallel to each other - unrelated to crystal structure e.g. quartz fractures but has no cleavage

cleavage has distinct regular patterns

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42
Q

what distinctive feature can you use to tell if it is a cleavage plane.

A

when the mineral brakes along the cleavage plane it will have a shiny/ reflective lustre due to the showing of a fresh plane of crystal.

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43
Q

if a mineral is idiochromatic we say that…

A

if a mineral is idiochromatic we say that the mineral has one distinctive colour that we can use to identify it. e.g native sulphur which is yellow

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44
Q

most minerals are allochromatic. this means…

A

most minerals are allochromatic. this means that the mineral can have variable colours due to different chemical or mineral impurities. e.g. quartz, flourite

this means that we shouldnt take colour as a major .factor in the identification of the rock

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45
Q

what is lustre?

A

lustre is the quality of light reflected and refracted by crystals.

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46
Q

__________ lustre is characteristic of transparent/ glassy minerals (i.e. most silicats, carbonates & sulphate minerals)

A

Vitreous lustre is characteristic of transparent/ glassy minerals (i.e most silicates, carbonates & sulphate minerals).

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47
Q

__________ lustre is characteristic of semi-transparent minerals

A

Resinous lustre is characteristic of semi-transparent minerals

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48
Q

_________ lustre is characteristic of opaque, highly reflective sulphide, oxide and native element minerals.

A

Metallic lustre characterises opaque highly reflective sulphide, oxide and native element minerals

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49
Q

________ lustre characterises very finely crystalline minerals

A

Earthy lustre characterises very finely crystalline minerals

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50
Q

________ lustre charaterises fibrous minerals

A

Silky lustre characterises fibrous minerals

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51
Q

what is luminescence?

A
  • Emission of light when mineral is irradiated, e.g. by UV light or an electron beam
  • Caused by defect in crystal structures or impurities
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52
Q

what is the difference between phosphorescence and fluorescence

A

Phosphorescence
Emission of light even after removal of UV radiation
Fluorescence (fluorite)
Emission of light only during UV irradiation

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53
Q

some of what type of minerals react with cold dilute HCL.

A

Some carbonate minerals react with cold dilute HCL and effervesce as carbon dioxide

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54
Q

which two minerals react with cold HCL?

A

calcite, aragonite (limestone) but other carbonate minerals only react in hot acid e.g. dolomite

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55
Q

name the most magnetic mineral

A

magnetite

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56
Q

which minerals have a high degree of radioactivity?

A

uranium and thorium

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57
Q

which two minerals have orthosilicate tetradhera structure?

A

garnet and olivine

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58
Q

which mineral is a chain silicate?

A

pyroxene

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59
Q

what are the two major types of pyroxenes and what is the diffence between the two?

A

Augite – stubby crystals - Ca clinopyroxene

aegirine –long crystals- Na clinopyroxene

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60
Q

for pyroxenes what two unit cell can they have and what name is then given to that mineral.

A

can be:

orthorhombic (orthopyroxenes)

monoclinic (clinopyroxenes)

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61
Q

give hardness, colour, habit, cleavage of pyroxene.

A

usually dark coloured but varies depending on Fe/Mg contents.

elongate prismatic habits but not acicular or fibrous.

intersecting cleavages at 87/93˚.

Hardness 5 – 6

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62
Q

define isomorphs

A

different chemical composition but same crystal structure

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63
Q

describe olivine interms of crystal, colour, cleavage, hardness and lustre.

A

olivines form equidimensional pale to dark green crystals

no apparent cleavage

hardness of 6½

victorious lustre

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64
Q

what is the unit cell of garnet? how can we tell?

A

cubic

as it has the same minimum symytery as a cube.

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65
Q

describe garnet in terms of crystal, colour, cleavage and hardness.

A

garnets form equi-dimensional dark crystals

no cleavage

hardness of 6 – 7½.

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66
Q

which mineral is a double chain silicate, linked lateally by various cations.

A

amphiboles

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67
Q

what are the two major types of amphibole?

A

hornblende

glaucophane (dark blue needle crystals)

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68
Q

ambibole and pryroxene look very similar to the eye.

how can we differentiate between amphibole and pyroxene?

A

easiest way is by looking at cleavage planes under cross section microscope.

amphibole has cleavage of 124/56º while pyroxene is more likely to be 90/90º

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69
Q

what habits can amphibole have?

A

elongate, acicular or fibrous habits.

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70
Q

describe amphiboles in terms of colour, cleavage, and hardness.

A

Fe/Mg varieties are dark coloured whereas the more Al rich varieties are light coloured.

cleavages at 124/56˚

Hardness = 5 – 6

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71
Q

what two minerals are sheet silicates?

A

mica

chlorite

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72
Q

what are the two major types of mica?

A

muscovite mica

biotite mica

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73
Q

whats the major difference between muscovite and biotite?

A

muscovite - usually colourless

biotite - dark brown (more black with more Fe)

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74
Q

what is the lustre, morphology, cleavage, hardness of both types of micas?

A

both muscovite and biotite have a pearly to vitreous lustre.

both exhibit a platy morphology; plates are flexible

one perfect basal cleavage

soft with a hardness of 2 to 3

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75
Q

what makes mica different to other silicates?

A

mica is much softer unlike other silicates

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76
Q

what is the unit cell of chlorites?

A

monoclinic

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77
Q

describe chlorites.

A

Chlorites are sheet silicates with a different crystal structure to that of the micas

In hand specimen chlorites are characteristically green in colour - green colour increases with increasing Fe contents.

They exhibit a platy morphology with one perfect basal cleavage

soft with a hardness of 2 to 3.

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78
Q

name the two soft silicates and why?

A

micas and chlorites due to them being sheet silcates thus can bend very easily.

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79
Q

name two minerals which have a framework silicate

A

quartz

feldspar

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80
Q

what is the unit cell of quartz

A

trigonal

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81
Q

describe quartz

A

no cleavage

hardness = 7

vitreous lustre

conchoidal fracture

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82
Q

when identifying quartz what shouldnt you use to identify it?

A

you shouldnt use colour as you get many coloured varieties due to chemical impurities. however quartz is normally colourless.

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83
Q

what is chalcedony?

describe it properties in terms of fracture and hardness

A

micro-crystalline quartz with sub-microscopic pore spaces infilled with water.

They grow into a cavity. Can be used as thin blades used in surgery.

massive with concoidal fracture

hardness - 7

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84
Q

what types of chalcedony are there?

A

Agate is a banded variety,

flint is a dark nodular variety

85
Q

what are feldspars?

A

Feldspars are framework silicates in which 25 to 50% of Si is replaced by Al and the change in balance is maintained by cations K, Na and Ca.

this is done in a particular way so that feldspar now has cleavage, unlike the other framework silicate, quartz

86
Q

what cation makes up alkali feldspars

A

potassium

87
Q

what cation makes up plagioclase feldspar?

A

calcium

88
Q

what happens to alkali feldspars above 700º and then what happens when it cools down?

A

above 700º it is a solution between k feldspars and Na feldspars.

cooling promotes unmixing and perthite textures

89
Q

descibe alkali feldspars in terms of colour, cleavage, lustre, hardness, texture, twinning.

A

colourless, however can be multiple colours, mainl pink.

two good intersecting cleavages 90º

vitreous lustre

hardness of 6 (less than quartz)

perthitic texture may be visible (tiger stripes (thin veins) in same direction)

may show simple of interpenetrative twinning

90
Q

whats the difference between plagioclase feldspar and alkali feldspar.

A

Plagioclase feldspars show complete solid solution at lower temperatures than alkali feldspars (we dont get this seperation when at a lower temp.)

plagioclase do not form perthitic structures

there are many different types of plagioclase feldspar based on the concentration of sodium and calcium.

plagioclase can have multiple polysynthetic twinning while orthoclase can have simple or interpenetrative twinning

91
Q

describe plagioclase feldspar interms of colour, cleavage planes, lustre, hardness, twinning, and texture

A

various colours or colourless,

good intersecting cleavage planes 90º

vitreous lustre,

hardness of 6: less than quartz,

may show polysynthetic twinning,

no perthitic cleavage.

92
Q

calcte and aragonite are polymorphs.

what does this mean?

A

Calcite and aragonite are polymorphs of CaCO3 – i.e same composition but different crystal structures.

93
Q

name the three major types of carbonates and describe the general properties of carbonates in terms of hardness, lustre, cleavage

A

calcite - trigonal

dolomite - trigonal

aragonite - orthorhombic

hardness < 5

vitreous lustre

trigonal carboantes are characterised by perfect rhombic cleavage

94
Q

how can you tell the carbonates apart?

A

calcite and aragonite are readily soluable in cold HCl, dolomite is not.

95
Q

whats the best test for halides?

A

chloride minerals have a salty taste

being readily soluable in water.

96
Q

what lustre is most oxides?

A

some but not all oxides are opaque with a metallic lustre.

97
Q

what characterises sulphides?

A

sulphides are opaque with characteristic metallic lustre.

98
Q

what unit cell is calcite?

A

trigonal

99
Q

what colour is dolomite usually?

A

brown

100
Q

what is the unit cell of dolomite?

A

trigonal

101
Q

what is the unit cell of aragonite?

A

orthorhombic

102
Q

what is the difference in the formation of calcite and aragonite ( they are isomorphs CaCO3)

A

calcite (low pressure, higher temperature)

aragonite (higer pressure, low temperature)

103
Q

describe carbonates in terms of hardness, lustre, cleavages.

A

generally have a hardness <5

vitreous lustre

trigonal carbonates have perfect rhombic cleavages.

104
Q

name the three main sulphates

A

gypsum

anhydrite

barite

105
Q

describe gypsum in terms of habits, twinning, hardness, cleavage

A

Tabular fibrous, granular, massive habits

  • often twinned
  • soft (H=2)
  • One perfect + 2 good cleavages
106
Q

what is the unit cell of gypsum ?

A

monoclinic

107
Q

anhydrite - gypsum without water.

describe anhydrite in terms of hardness, cleavage, and habits

A
  • H= 3-5
  • 3 good/perfect intersecting cleavages at right angles
  • fibrous, granular habits
108
Q

what is the unit cell of barite?

A

orthorhombic

109
Q

describe barite in terms of cleavage, density, habit

A
  • two- three cleavage planes, at least one perfect.
  • Denser than usual in vitreous minerals, platy habit
110
Q

what are the general properties of sulphates in terms of hardness, lustre, and where do they normally occur.

A

Sulphates usually have hardness < 4 and show Vitreous to pearly lustre. Usually occur in evaporate deposits

111
Q

name the two major types of halides.

A

halite

flourite

112
Q

what is the unit cell of halite and flourite.

A

cubic

113
Q

what is the hardness and cleavage of halite?

A

h<3

three perfect cleavage planes

114
Q

what is the hardness, cleavage, colour and streak of flourite?

A

h<4

4 perfect cleavage planes

variable colours

white streak

115
Q

what are the major three oxides?

A

hematite

magnetite

corrundum

116
Q

what are the unit cell of magnetite and hematite?

A

cubic

117
Q

what mineral is this?

A

hematite

118
Q

what is the unit cell, hardness and lustre of corundum?

A

trigonal

hardness = 9

vitreous-resinous lustre

119
Q

what is a distinctive feature of oxides?

A

they have a red brown streak

120
Q

what are the general properties of oxides, in terms of lustre, hardness, cleavage, streak?

A

most but not all oxides are opaque with a metallic lustre.

hardness usually >= 5

no cleavage planes

red-brown streak

121
Q

what are the major four sulphides? and what are the unit cell for all sulphides?

A

pyrite

galena

chalcopyrite

sphalerite

they are all cubic unit cell

122
Q

what are the general properties of sulphides in terms of lustre, hardness, cleavage?

A

are opaque with characteristic metallic lustre

hardness <= 6

variable cleavages

123
Q

what does idiocratic and monocratic mean?

A

Idiocratic – different colours
Monocratic - all the same colour

124
Q

describe the basic rock formation of igneous, sedimentary and metamorphic rocks.

A

igneous

  • melting in crust and upper mantle
  • cooling and crystallisation

sedimentary

  • weathering and erosion at surface (+biological inout)
  • deposition, burial, dewatering, lithification

metamorphic

  • alteration by high temperature and/or pressure at depth
  • recrystallisation and new minerals
125
Q

what are the relative proportions of the crust and land surface in terms of igneous and sedimentary?

A

crustal volume

~95% igenous

~5% sedimentary

land surface area

~ 75% sedimentary

~ 25% igneous

126
Q

how are igneous rocks formed?

A

igneous rocks form by the crystallisation from magmas in the crust or at the surface

127
Q

magmas of different composition originate via …

A

magmas of different compositions originate via melting of different source rocks in the lower crust and mantle.

128
Q

melting is controlled by:

A

melting is controlled by:

source rock composition

water contents

pressure

temperature

129
Q

where would you find acid (silicic) rocks, intermediate rocks (contaminated), and basaltic (basic) rocks.

A

acid (silic) rocks: continental setting

intermediate rocks (contaminated): convergent margins

basaltic (basic) rocks (primary magmatic source): mid-oceanic ridges/hotspots

130
Q

what is the correlation between crustal depth and crystal size?

A

extrusive

rapid cooling - smaller crystals/glass

intrusive

slow cooling - larger crystals

131
Q

describe extrusive (volcanic) igneous rocks

A
  • form by rapid crystallisation from magmas at the surface
  • characterised by volcanic glass (e.g. obsidian)
  • and/or fine grained crystals (e.g. basalt)

-two major types:

lavas - formiing flows

pyroclastics - forming deposits of volcanic fragments

-both may be found in most volcanic settings

132
Q

describe volcanic rocks interms of texture and appearance.

A

lavas show a variety of textures

escaping gas creates holes or vesicles

some lavas contain large crystals (phenocrysts) formed during slower cooling to poduce a porhyritic texture

pyroclastics (or tuffs) form from violent explosive eruptions

ash and lava fragments formed often compact and weld together when hot.

133
Q

what are phenocrysts and what is the associated texture?

A

phenocrysts are large crystals found in lavas which are formed during slow cooling

the associated texture is a porphyritic texture

134
Q

what is meant by a vesicular texture?

A

vesicular texture

texture produced by escaping gas bubbles.

some gas bubbles infilled by minerals (amygdales)

135
Q

name the three products of volcanic eruption

A

**glass **

-obsidian

pyroclastics

  • ash
  • pumice
136
Q

what is a welded tuff?

A

welded tuff

volcanic ash flow with flattened and deformed volcanic clasts and glass

137
Q

describe intrusive or plutonic igneous rocks.

A

intrusive or plutonic igneous rocks

  • form by slow crystallisation from magmas below the earth’s surface
  • composed entirely of coarse interlocking crystals (holocrystalline)
138
Q

what are the three major types of intrustive/plutonic rocks?

A

granite (acidic)

diorite (intermediate)

gabbro (basic)

139
Q

describe the colour variations between gabbro, diorite and granite.

A

gabbro - dark coloured (limited colour variation)

diorite - intermediate in colour, often with more feldspars

granite - lighter coloured (more colour variation)

140
Q

plutonic rocks

the larger the body, _________ the grain size.

the larger the body, ___________ the crustal setting

A

plutonic rocks

the larger the body, coarser the grain size.

the larger the body, deeper the crustal setting

141
Q

name the larger and deeper igneous intrusives and the shallower intrusives.

A

plutons: deep, large bodies (e.g. bastholiths)

shallower intrusives: sills, dykes

142
Q

which direction do sills and dykes go in?

A

dykes - vertical sheets

sills - horizontal sheets

143
Q

what is a sill?

A

sill: an intrusive, concordant, igneous rock body forced between parallel strata

144
Q

what is a dyke?

A

dyke: an intrusive, discordant, igneous rock body cross-cutting sedimentary layers (vertical to sub vertical

145
Q

what is meant by holocrystalline, hypocrystalline, and holohyaline?

A

interlocking crystals - holocrystalline

glass plus crystals - hypocrystalline

glass only - holohyaline

146
Q

in terms of igneous rock crystal shapes, what does euhedral, subhedral, and anhedral mean?

A

euhedral - well developed crystal shapes with preserved faces; usually phenocrysts

subhedral - some well-developed crystal shapes with preserved faces

anhedral - no well-developed crystal shapes and ne preserved faces

147
Q

igneous rock textures.

name and describe the seven igneous rock textures.

A

granular - uniform sized medium to coarse crystals

aphnitic - uniformily fine grained; cannot differentiate individual crystals with the naked eye

granitic - irregular mixture of euhedral, subhedral, and anhedral crystals

porphyritic - large phenocrysts in finer grained groundmass

vesicular - cavities caused by escape of gas bubbles

amygdalidal - cavities later infilled with crystals

poikilitic - later crystallising mineral encloses smaller earlier forming crystals.

148
Q

silicate minerals characterise igneous rocks

most common are:

A

silicate minerals characterise igneous rocks

most common are:

quartz, feldspar, micas, pyroxenes, amphboles, olivines

149
Q

whats the major difference between mafic and felsic?

A

mafic (e.g. gabbro, basalt) is normally dark in colour

felsic (e.g. granite) is light in colour

150
Q

origin of magmas

magmas vary: from melting of mixed source rocks in upper mantle and crust

______________: rocks in upper mantle melt partially

____________: mixtures of sedimentary and basaltic rocks in subduction zones

__________: mixtures of sedimentary, igneous and metamorphic rocks

A

origin of magmas

magmas vary: from melting of mixed source rocks in upper mantle and crust

basaltic magmas: rocks in upper mantle melt partially

intermediate magmas: mixtures of sedimentary and basaltic rocks in subduction zones

granitic magmas: mixtures of sedimentary, igneous and metamorphic rocks

151
Q

describe briefly Bowen’s reaction series.

A

tried to explain how basaltic magma cooled and evolved

‘fractional crystallisation’ (formation of crystals at different times) gives silica rich magmas

152
Q

what are clastic sediments?

A

they are sediments that are created by weathering, erosion and deposition

153
Q

what are the main two types of sediments?

describe them.

A

clastic sediments - derived from weathering )can be physical, freeze-thaw, or chemical) and erosion of pre-existing rocks and transported bywater, wind and ice before deposition

biogenic and chemical sediments- form as biochemical or inorganic chemical precipitates e.g. skeletal fragments (shelly fragments) in limestones; evaporites

154
Q

what is lithification?

A

lithification converts sediments into sedimentary rocks by compaction or cementation by new minerals precipitating out of pore fluids

155
Q

what is diagenesis?

A

diagenesis describes all the physical, chemical, and biological processes that affect sediments after deposition

156
Q

name the major siliciclastics, calciclastics, biogenic sediments, and evaporites.

A

siliciclastics - quartz, feldspars, clay minerals, rock fragment (silica rich)

BUT weathering and erosion of carbonate rocks will yield clasts of carbonate composition – calciclastics – calcite, dolomite.

biogenic sediments aragonite, calcite, opaline silica and quartz (chalcedony silica (flint) occurs as subsiduary

evaporites halite, gypsum and anhydrite Dolomite occurs in evaporites but also forms via dolomitisation of calcite

157
Q

what are conglomerates and breccias and how are they differentiated?

A

conglomerates and bressias are dominated by clasts >2mm in size.

clasts are composed mainly of rock fragments rather than single minerals.

if a matrix is present it will be mud or sand grade.

post depositional diagenetic crystalline cements may also be present in variable amounts.

conglomerates have rounded clasts while breccias have mainly angular clasts reflecting the degree of transport before deposition.

158
Q

what is meant by ortho-conglomerate and para-conglomerate?

A

ortho-conglomerate: clast supported

para-conglomerate: matrix supported

159
Q

clast type

define monomict, polymict, and diamict

A

clast type

monomict - clasts of mainly one composition

polymict - clasts of various composition

diamict - clasts poorly sorted of various types (mainly matrix supported)

160
Q

what is the difference between matrix and cement?

A

matrix - original, primary, finer sediment between major clasts, allogenic - made of the same type

cements - bind clast/matrix (secondary, crystalline, diagenetic - forms after, typically calcite, silica (fills in spore spaces)

161
Q

what is a sandstone?

A

sandstones are dominated by clasts of sand grade that vary from angular to rounded depending on degree of transport before deposition.

matrix, if present, will be of mud grade. diagenetic crystalline cements are common and of various compositions .e.g. quartz, calcite, clay minerals but difficult to see in hand specimens.

162
Q

what is sorting?

A

degree and length of transport can also effect sorting. well sorted sands have a narrow range in grain sizes within the sand rades whereas poorly sorted sands have widely varying sizes within and outside the sand grades.

163
Q

describe a quartz arenite.

A

usually white or pale coloured sandstone composed of 90% quartz grains. the term arenite implies that the rock is dominated by more than 85% sand sized grains.

164
Q

what is meant by the term arenite?

A

the term arentite implies that the rock is dominated by more than 85% sand sized grains.

165
Q

describe arkose/ feldspathic arenite

A

usually pale brown to cream coloured sandstone containing more than 25% feldspar grains

166
Q

describe lithic arenite.

A

often dark coloured sandstone with more than 25% of sand-sized fine grained rock fragments such as mudrocks, slates or volcanics

167
Q

describe a grey wacke.

A

dark coloured sandstone containing 15-20% mud grade matrix as well as poorly sorted quartz, felspar or lithic sand grains. can have different varieties depending on dominent composition of sand grains e.g. quartz wacke, lithic wacke, etc.

168
Q

what is the pettijohn classification?

A

it is based on percentage of matrix

  • matrix poor (<15%) - arenites
  • matrix rich (>15%) - wackes
169
Q

name three fine grained siliciclastic rocks.

A

fine grained siliciclastic rocks

mudstones

siltstones

shales

170
Q

what is meant by fissility?

A

fissility - a tendency to split along thin bedding planes or laminae, which mudstones and siltstones do not have.

171
Q

describe shales.

A

shales are characterised by fissility, a tendency to split along thin bedding planes or laminae, which mudstones and siltstones do not have. in addition to quartz and feldspar the mudstones and shales are usually dominated by the presence of clay mineral, fine graied sheet silicates

172
Q

whats the difference between shale and slate?

A

shale - splits along bedding planes

slate - splits on cleavage planes

173
Q

what is meant by textural and mineralogical maturity in sedimentary rocks?

A

maturity is a function of sediment transport

textural maturity refers to:

  • the degree of roundness of the grains
  • the amount of sorting of the grain sizes

texturally mature sandstones have well-rounded and well sorted grains, immature if not.

mineralogical maturity refersto the percentage of quartz grains

  • feldspars break down under transport
  • quartz grains are more resistant due to hardness

mineralogically mature sandstones have the most quartz grains

arkose thus is mineralogically immature.

174
Q

what are carbonates?

A

carbonates

are biogenic minerals

sometimes inorganic precipitats from carbonate saurated waters

common in warm, high productivity seas (near the equator)

175
Q

describe the classification of carbonates.

where do teh names dolostone and dolomitic limestone come from?

A

by definiton carbonate rocks have more than 50% CaCO3 mainly as calcite (CaCO3) in limestones but also as dolomite (CaMg(CO3)2)

carbonates can be amde of hard (reefs) or from soft grains.

if dolomite predominates rock it is referred to as a dolostone

if calcite > dolomite and dolomite > 10% its called a dolomitic limestone

176
Q

name and describe three carbonate facies.

A

reefs

  • high productivity
  • CaCO3 shells
  • complicated physical structures
  • lagoon - burrows

shoals

  • high carbonate production rates
  • high degree of agitation (waves go back and for to make constant symmetrical ripples)
  • precipitation of carbonate ooids (made like a snowball when a central grain has CaCO3 rolled on top)

pelagic

  • algal blooms –> CaCO3 grains produced
  • coccoliths - make up the white cliffs of dover
  • there is also foraminifera - fine grained chalk with courser flint.
177
Q

many siliclastic rocks cotain carbonates as _________ and ________

A

many siliclastic rocks contain carboantes as fossils (bioclasts) and as crystalline cement (spar)

178
Q

because limestones show limited mineralogical/chemical variability the limestones rocks are classified on the basis of textural variations.

what are the three major compoents and describe them.

A

the three major components are:

carbonate grains or allochems

  • composed of skeletal/shell material - bioclasts
  • precipitated carbonate forming spherical coated grains or ooids
  • ovoid aggregates of carbonate mud or peloids
  • clasts of previously formed limestones or partly lithified carbonate carbonate sediments - aggregates or intraclasts

carbonate mud or micrite

cements - usually carbonate compositions

179
Q

what are calcirudites, calarenites, and calcilutites?

A

calcirudites - carbonate grains predominantly greater than 2mm

calarenites - (calcareous sandstones) carbonate grains predominantly of sand grade (2mm - 0.063mm)

calcilutites - (calcareous mudstones or micrite) carbonate grains predominantly of mud grade (<0.063mm)

180
Q

useing the folk classification of limestones

what are the four prefixes and the surffix when cemented by sparite and a micritic matrix.

A

skeletal grains - bioclasts - bio-

ooids - oo

peloids - pel

intraclasts - intra

cemented by sparite -sparite

micritic matrix -micrite

thus ooids cemented by sparite would be oosparite

and peloids with a micritic matrix would be pelmicrite.

181
Q

what are the four main allochem types?

A

skeletal/ shell material - bioclasts

precipitated carbonate, forming spherical coated grains - ooids

ovoid aggregates of carbonate mud - peloids - poop from creatures

limestone clasts or partly lithified carbonate sediments - intraclasts.

182
Q

what are pisoliths?

A

pisoliths are ooids bounded together

183
Q

what are ooids?

A

concentric

nucleus, skeletal fragment or quartz grain.

184
Q

what is the dunham classifying system based on?

A

the dunham classifying system is based on the presence of mud matrix and grain/ mud support

185
Q

what are the five classifications of the dunham system. describe them.

A

mudstone - less than 10% grains (mud supported)

wackestone - more than 10% grains (mud supported)

packstone - (contains mud)(grain supported)

grainstone - (lacks mud)(grain supported)

boundstone - original components bound together at deposition. intergrown skeletal material, liamination contrary to gravity, or cavities floored by sediment, roofed over by organic material but too large to be interstices.

186
Q

what are evaporites?

A

evaporites

chemical precipitates from super saturated solutions

usually associated with low rainfall/ aridity plus high evaporation rates

dead seas - large amounts of salt

marine and non-marine evaporates common

produced during greenhouse time periods

187
Q

explain how evaporite minerals form.

A

evaporite minerals

minerals precipitate out in definite order:

least soluable first (carbonates)

then gypsum

followed by halite

then the K/Mg salts

188
Q

to what depths and temperatures does metamorphism happen to?

A

up to 35km

200 - 700 degrees

189
Q

what are the two types of metamorphism?

A

regional metamorphism

occurs over large areas of the crust subjected to high temperatures and pressures

**contact thermal metamorphism **

occurs over localised areas adjacent to igneus intrusions causing mainly an increase in temperature but also pressure in some instances

190
Q

what effects the mineralogy of metamorphic rocks?

A

temperature

pressure

source rock

191
Q

whats the difference between calcite, shale, and basalt as they are metamorphosed?

A

calcite will usually recrystallise

shale and basalt will go under different mineralogical changes.

192
Q

what do metamorphic facies help us to define?

A

metamorphic facies help us to define the conditions of temperature and/or pressure

193
Q

what are metamorphic facies defined by?

A

metamorphic facies are defined by the rock texture (foliation, granularity, etc) and new mineral growth

194
Q

what are isograds?

A

isograds

lines on a geological map to show locations of first appearance of index minerals and represent sets of conditions satisfying the reaction equilibrium of the metamorphic reaction.

195
Q

what is foliation?

A

foliation

caused principally by the alignment of platy minerals e.g. micas and chlorites perpendicular to the principal deformation stress direction.

pressure induces reorganisation and growth of new minerals: creating foliation

196
Q

what are the four main foliated matamorphic rocks?

put them in order of grade from smallest to highest grade

what feature shows you the grade of the rock?

A

slate

phyllite

schist

gneiss

splitting surfaces is low grade coaser grade foliation, distinct banding is higher grade.

197
Q

describe slates.

A

lowest grade of foliated rocks

produced usually by regional metamorphism of shales or fine grained volcanics

will split along foliation planes developed by platy micas and chlorite

there are spotted slates which indicate presence of small irregular porphyroblasts of minerals such as cordierite and andalusite that form during low grade metamorphism at low temperatures

198
Q

describe phyllite

A

slightly higher grade than slate

often foliation planes

glossy sheen due to presence of larger crystals of micas and chlorites than in slates.

199
Q

descirbe schists

A

foliation planes have a highly reflective sheen due to presence of coarse micas and chlorites that make up 50% of the rock

within the foliated textures of schists new metamorphic minerals may grow as large crystals within the matrix, porphyroblasts

200
Q

describe gneisses

A

coarser foliation than in the schists either reflecting a greater degree of metamorphism than the schists with micas and chlorites reacting to form new assemlages more dominated by quartz and feldspar or develop rather than schists if coarser sediments or igneous rocks are metamorphosed.

201
Q

name three non-foliated metamorphic rocks.

A

hornfels (spotted hornfels)

quartzites

marbles

202
Q

what is meant by granoblastic texture?

A

metamorphic rocks show uniform crystal size

203
Q

describe schistosity

A

wavy foliation, parallel mica growth, often with porphyroblasts of garnet

204
Q

describe hornfels

A

dense

uniform grain size

formed by high temperature, low pressure contact metamorphism

platy or elongated minerals showing no preferred orientation

spotted hornfels

spotted due to the prescence of small irregular porphyroblasts of mineral such as cordierite and andalusite that form during meta morphic heating at low pressures.

205
Q

describe quartzite

A

metamorphosed quartz

rich sandstones and metamorphism produces a rock of recrystallised uniform sized quartz crystals with no foliation.

can form under regional and contact metamorphic conditions

206
Q

describe marbles

A

metamorphosed limestone

equi-granular interlocking recrystallised calcite crystals with no foliation.

can form under regional and contact metamorphism

207
Q

what is contact metamorphism?

what controls its extent?

A

baking of a country rock by igneous intrusions

extent is controlled by size of the body. larger intrusions create an aureole surrounding the intrusion

208
Q
A

geophysics (9 decks)

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