earth materials Flashcards
1
Q
define a mineral
A
minerals are naturally occuring, homogenous, crytalline solid with a definite crystalline chemical composition
2
Q
what is continuous and constant throughout the mineral structure.
A
• Atomic structure is continuous and constant throughout the mineral structure
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.
4
Q
what does consolidated mean?
A
it means the rock is firm
5
Q
what does non-consolidated mean?
A
it means the rock is loose
6
Q
what is concrete?
A
a non-natural aggregate of other rocks set in a matrix
7
Q
coal, limestone, evaporite. are they biogenic or inorganic?
A
coal - biogenic
limestone - biogenic
evaporite - inorganic
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
9
Q
what is the length of an angstrom?
A
1A = 10-10m
10
Q
cubic = …
A
CUBIC
a = b = c; α = β = γ = 90
11
Q
tetragonal = …
A
TETRAGONAL
a = b != c; α = β = γ = 90
12
Q
orthorhombic = …
A
ORTHORHOMBIC
a != b != c; α = β = γ = 90
13
Q
monoclinic = …
A
MONOCLINIC
a != b != c; α = γ = 90 β > 90
14
Q
triclinic = …
A
TRICLINIC
a != b != c; α != β != γ != 90
15
Q
hexagonal
A
HEXAGONAL
a = b != c; α = β = 90; γ =120
16
Q
trigonal - rhombohedral
A
TRIGONAL - Rhombohedral
a = b = c; α = β = γ != 90 < 120
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
18
Q
symmetry is a defining property of…
A
Symmetry is a defining property of a crystal
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 **
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.
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
22
Q
define habit
A
habit describes the general shape of a crystal or crystal aggregate
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.
24
Q
what is nomenclature
A
they are terms to describe the form of naturally occuring minerals
25
what is the nomenclauture of this rock?
prismatic habit
26
what is the nomenclauture of this rock?
tabular habit (looks like tables on top of each other)
27
what is the nomenclauture of this mineral?
platy habit
28
what is the nomenclauture of this rock?
fibrous habit
29
what is the nomenclauture of this rock?
accicular habit
30
what is the nomenclauture of this rock?
nodular radiating habit
31
what is the nomenclauture of ths rock?
botryoidal habit
32
what is the nomenclauture of this rock?
dendritic habit
33
when does twinning occur?
it can occur during crystal growth, or by the deformation during the formation of the rock
34
what is twinning?
twinned crystals have two or more parts that are physically continuous.
35
name the three typical types of twinning found in minerals
simple
repeat/ polysyntheitc
interpenetrant (two cubes penetrating each other)
36
name two factors that effect density.
mass of the individual atoms
the packing of the atoms
37
where do fingernail, copper coin and steel knife blade come on the moh's scale of hardness?
fingernail - 2.5
copper coin - 3.5
steel knife blade - 6.5
38
give the general hardness of these mineral groups
silicates
sulphides
oxides
carbonates, sulphates
Silicates 5 – 8
Sulphides \<6
Oxides \>6
Carbonates, sulphates \<5
39
hardness generally increases with...
Hardness generally increases with density
Calcite CaCO3 D = 2.71 g/ml H = 3
Aragonite CaCO3 D = 2.93 g/ml H = 4
40
what is mineral cleavage?
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)
41
whats the difference between cleavage and fracture?
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
42
what distinctive feature can you use to tell if it is a cleavage plane.
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.
43
if a mineral is idiochromatic we say that...
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
44
most minerals are allochromatic. this means...
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
45
what is lustre?
lustre is the quality of light reflected and refracted by crystals.
46
\_\_\_\_\_\_\_\_\_\_ lustre is characteristic of transparent/ glassy minerals (i.e. most silicats, carbonates & sulphate minerals)
Vitreous lustre is characteristic of transparent/ glassy minerals (i.e most silicates, carbonates & sulphate minerals).
47
\_\_\_\_\_\_\_\_\_\_ lustre is characteristic of semi-transparent minerals
Resinous lustre is characteristic of semi-transparent minerals
48
\_\_\_\_\_\_\_\_\_ lustre is characteristic of opaque, highly reflective sulphide, oxide and native element minerals.
Metallic lustre characterises opaque highly reflective sulphide, oxide and native element minerals
49
\_\_\_\_\_\_\_\_ lustre characterises very finely crystalline minerals
Earthy lustre characterises very finely crystalline minerals
50
\_\_\_\_\_\_\_\_ lustre charaterises fibrous minerals
Silky lustre characterises fibrous minerals
51
what is luminescence?
* Emission of light when mineral is irradiated, e.g. by UV light or an electron beam
* Caused by defect in crystal structures or impurities
52
what is the difference between phosphorescence and fluorescence
**Phosphorescence**
Emission of light even after removal of UV radiation
**Fluorescence (fluorite)**
Emission of light only during UV irradiation
53
some of what type of minerals react with cold dilute HCL.
Some **carbonate minerals** react with cold dilute HCL and effervesce as carbon dioxide
54
which two minerals react with cold HCL?
**calcite**, aragonite (**limestone**) but other carbonate minerals only react in hot acid e.g. dolomite
55
name the most magnetic mineral
magnetite
56
which minerals have a high degree of radioactivity?
uranium and thorium
57
which two minerals have orthosilicate tetradhera structure?
garnet and olivine
58
which mineral is a chain silicate?
pyroxene
59
what are the two major types of pyroxenes and what is the diffence between the two?
**Augite** – stubby crystals - Ca clinopyroxene
**aegirine** –long crystals- Na clinopyroxene
60
for pyroxenes what two unit cell can they have and what name is then given to that mineral.
can be:
**orthorhombic (orthopyroxenes)**
**monoclinic (clinopyroxenes)**
61
give hardness, colour, habit, cleavage of pyroxene.
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
62
define isomorphs
different chemical composition but same crystal structure
63
describe olivine interms of crystal, colour, cleavage, hardness and lustre.
olivines form equidimensional pale to dark green crystals
no apparent cleavage
hardness of 6½
victorious lustre
64
what is the unit cell of garnet? how can we tell?
cubic
as it has the same minimum symytery as a cube.
65
describe garnet in terms of crystal, colour, cleavage and hardness.
garnets form equi-dimensional dark crystals
no cleavage
hardness of 6 – 7½.
66
which mineral is a double chain silicate, linked lateally by various cations.
amphiboles
67
what are the two major types of amphibole?
hornblende
glaucophane (dark blue needle crystals)
68
ambibole and pryroxene look very similar to the eye.
how can we differentiate between amphibole and pyroxene?
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
69
what habits can amphibole have?
elongate, acicular or fibrous habits.
70
describe amphiboles in terms of colour, cleavage, and hardness.
Fe/Mg varieties are dark coloured whereas the more Al rich varieties are light coloured.
cleavages at 124/56˚
Hardness = 5 – 6
71
what two minerals are sheet silicates?
mica
chlorite
72
what are the two major types of mica?
muscovite mica
biotite mica
73
whats the major difference between muscovite and biotite?
muscovite - usually colourless
biotite - dark brown (more black with more Fe)
74
what is the lustre, morphology, cleavage, hardness of both types of micas?
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
75
what makes mica different to other silicates?
mica is much **softer** unlike other silicates
76
what is the unit cell of chlorites?
monoclinic
77
describe chlorites.
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.
78
name the two soft silicates and why?
**micas and chlorites** due to them being sheet silcates thus can bend very easily.
79
name two minerals which have a framework silicate
quartz
feldspar
80
what is the unit cell of quartz
trigonal
81
describe quartz
no cleavage
hardness = 7
vitreous lustre
conchoidal fracture
82
when identifying quartz what shouldnt you use to identify it?
you shouldnt use colour as you get many coloured varieties due to chemical impurities. however quartz is normally colourless.
83
what is chalcedony?
describe it properties in terms of fracture and hardness
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
84
what types of chalcedony are there?
Agate is a banded variety,
flint is a dark nodular variety
85
what are feldspars?
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
what cation makes up alkali feldspars
potassium
87
what cation makes up plagioclase feldspar?
calcium
88
what happens to alkali feldspars above 700º and then what happens when it cools down?
above 700º it is a solution between k feldspars and Na feldspars.
cooling promotes unmixing and perthite textures
89
descibe alkali feldspars in terms of colour, cleavage, lustre, hardness, texture, twinning.
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
whats the difference between plagioclase feldspar and alkali feldspar.
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
describe plagioclase feldspar interms of colour, cleavage planes, lustre, hardness, twinning, and texture
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
calcte and aragonite are polymorphs.
what does this mean?
Calcite and aragonite are polymorphs of CaCO3 – i.e same composition but different crystal structures.
## Footnote
93
name the three major types of carbonates and describe the general properties of carbonates in terms of hardness, lustre, cleavage
calcite - trigonal
dolomite - trigonal
aragonite - orthorhombic
hardness \< 5
vitreous lustre
trigonal carboantes are characterised by perfect rhombic cleavage
94
how can you tell the carbonates apart?
calcite and aragonite are readily soluable in cold HCl, dolomite is not.
95
whats the best test for halides?
chloride minerals have a salty taste
being readily soluable in water.
96
what lustre is most oxides?
some but not all oxides are opaque with a **metallic lustre**.
97
what characterises sulphides?
sulphides are opaque with characteristic metallic lustre.
98
what unit cell is calcite?
trigonal
99
what colour is dolomite usually?
brown
100
what is the unit cell of dolomite?
trigonal
101
what is the unit cell of aragonite?
orthorhombic
102
what is the difference in the formation of calcite and aragonite ( they are isomorphs CaCO3)
calcite (low pressure, higher temperature)
aragonite (higer pressure, low temperature)
103
describe carbonates in terms of hardness, lustre, cleavages.
generally have a hardness \<5
vitreous lustre
trigonal carbonates have perfect rhombic cleavages.
104
name the three main sulphates
gypsum
anhydrite
barite
105
describe gypsum in terms of habits, twinning, hardness, cleavage
Tabular fibrous, granular, massive habits
- often twinned
- soft (H=2)
- One perfect + 2 good cleavages
106
what is the unit cell of gypsum ?
monoclinic
107
anhydrite - gypsum without water.
describe anhydrite in terms of hardness, cleavage, and habits
- H= 3-5
- 3 good/perfect intersecting cleavages at right angles
- fibrous, granular habits
108
what is the unit cell of barite?
orthorhombic
109
describe barite in terms of cleavage, density, habit
- two- three cleavage planes, at least one perfect.
- Denser than usual in vitreous minerals, platy habit
110
what are the general properties of sulphates in terms of hardness, lustre, and where do they normally occur.
Sulphates usually have hardness \< 4 and show Vitreous to pearly lustre. Usually occur in evaporate deposits
111
name the two major types of halides.
halite
flourite
112
what is the unit cell of halite and flourite.
cubic
113
what is the hardness and cleavage of halite?
h\<3
three perfect cleavage planes
114
what is the hardness, cleavage, colour and streak of flourite?
h\<4
4 perfect cleavage planes
variable colours
white streak
115
what are the major three oxides?
hematite
magnetite
corrundum
116
what are the unit cell of magnetite and hematite?
cubic
117
what mineral is this?
hematite
118
what is the unit cell, hardness and lustre of corundum?
trigonal
hardness = 9
vitreous-resinous lustre
119
what is a distinctive feature of oxides?
they have a red brown streak
120
what are the general properties of oxides, in terms of lustre, hardness, cleavage, streak?
most but not all oxides are opaque with a metallic lustre.
hardness usually \>= 5
no cleavage planes
red-brown streak
121
what are the major four sulphides? and what are the unit cell for all sulphides?
pyrite
galena
chalcopyrite
sphalerite
they are all cubic unit cell
122
what are the general properties of sulphides in terms of lustre, hardness, cleavage?
are opaque with characteristic metallic lustre
hardness \<= 6
variable cleavages
123
what does idiocratic and monocratic mean?
Idiocratic – different colours
Monocratic - all the same colour
124
describe the basic rock formation of igneous, sedimentary and metamorphic rocks.
**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
what are the relative proportions of the crust and land surface in terms of igneous and sedimentary?
**crustal volume**
~95% igenous
~5% sedimentary
**land surface area**
~ 75% sedimentary
~ 25% igneous
126
how are igneous rocks formed?
igneous rocks form by the crystallisation from magmas in the crust or at the surface
127
magmas of different composition originate via ...
magmas of different compositions originate via melting of different source rocks in the lower crust and mantle.
128
melting is controlled by:
**melting is controlled by:**
source rock composition
water contents
pressure
temperature
129
where would you find acid (silicic) rocks, intermediate rocks (contaminated), and basaltic (basic) rocks.
**acid (silic) rocks**: continental setting
**intermediate rocks (contaminated)**: convergent margins
**basaltic (basic) rocks (primary magmatic source)**: mid-oceanic ridges/hotspots
130
what is the correlation between crustal depth and crystal size?
**extrusive**
rapid cooling - smaller crystals/glass
**intrusive**
slow cooling - larger crystals
131
describe extrusive (volcanic) igneous rocks
- 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
describe volcanic rocks interms of texture and appearance.
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
what are phenocrysts and what is the associated texture?
phenocrysts are large crystals found in lavas which are formed during slow cooling
the associated texture is a porphyritic texture
134
what is meant by a vesicular texture?
**vesicular texture**
texture produced by escaping gas bubbles.
some gas bubbles infilled by minerals (amygdales)
135
name the three products of volcanic eruption
**glass **
-obsidian
**pyroclastics**
- ash
- pumice
136
what is a welded tuff?
**welded tuff**
volcanic ash flow with flattened and deformed volcanic clasts and glass
137
describe intrusive or plutonic igneous rocks.
**intrusive or plutonic igneous rocks**
- form by slow crystallisation from magmas below the earth's surface
- composed entirely of coarse interlocking crystals (holocrystalline)
138
what are the three major types of intrustive/plutonic rocks?
granite (acidic)
diorite (intermediate)
gabbro (basic)
139
describe the colour variations between gabbro, diorite and granite.
**gabbro** - dark coloured (limited colour variation)
**diorite** - intermediate in colour, often with more feldspars
**granite** - lighter coloured (more colour variation)
140
plutonic rocks
the larger the body, _________ the grain size.
the larger the body, ___________ the crustal setting
plutonic rocks
the larger the body, coarser the grain size.
the larger the body, deeper the crustal setting
141
name the larger and deeper igneous intrusives and the shallower intrusives.
plutons: deep, large bodies (e.g. bastholiths)
shallower intrusives: sills, dykes
142
which direction do sills and dykes go in?
dykes - vertical sheets
sills - horizontal sheets
143
what is a sill?
sill: an intrusive, concordant, igneous rock body forced between parallel strata
144
what is a dyke?
dyke: an intrusive, discordant, igneous rock body cross-cutting sedimentary layers (vertical to sub vertical
145
what is meant by holocrystalline, hypocrystalline, and holohyaline?
interlocking crystals - holocrystalline
glass plus crystals - hypocrystalline
glass only - holohyaline
146
in terms of igneous rock crystal shapes, what does euhedral, subhedral, and anhedral mean?
**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
igneous rock textures.
name and describe the seven igneous rock textures.
**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
silicate minerals characterise igneous rocks
most common are:
silicate minerals characterise igneous rocks
most common are:
quartz, feldspar, micas, pyroxenes, amphboles, olivines
149
whats the major difference between mafic and felsic?
**mafic** (e.g. gabbro, basalt) is normally dark in colour
**felsic** (e.g. granite) is light in colour
150
**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
**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
describe briefly Bowen's reaction series.
tried to explain how basaltic magma cooled and evolved
'fractional crystallisation' (formation of crystals at different times) gives silica rich magmas
152
what are clastic sediments?
they are sediments that are created by weathering, erosion and deposition
153
what are the main two types of sediments?
describe them.
**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
what is lithification?
**lithification** converts sediments into sedimentary rocks by **compaction** or **cementation** by new minerals precipitating out of pore fluids
155
what is diagenesis?
diagenesis describes all the physical, chemical, and biological processes that affect sediments after deposition
156
name the major siliciclastics, calciclastics, biogenic sediments, and evaporites.
**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
what are conglomerates and breccias and how are they differentiated?
**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
what is meant by ortho-conglomerate and para-conglomerate?
**ortho-conglomerate**: clast supported
**para-conglomerate**: matrix supported
159
**clast type**
define monomict, polymict, and diamict
**clast type**
**monomict** - clasts of mainly one composition
**polymict** - clasts of various composition
**diamict** - clasts poorly sorted of various types (mainly matrix supported)
160
what is the difference between matrix and cement?
**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
what is a sandstone?
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
what is sorting?
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
describe a quartz arenite.
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
what is meant by the term arenite?
the term arentite implies that the rock is dominated by more than 85% sand sized grains.
165
describe arkose/ feldspathic arenite
usually pale brown to cream coloured sandstone containing more than 25% feldspar grains
166
describe lithic arenite.
often dark coloured sandstone with more than 25% of sand-sized fine grained rock fragments such as mudrocks, slates or volcanics
167
describe a grey wacke.
**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
what is the pettijohn classification?
it is based on percentage of matrix
- matrix poor (\<15%) - arenites
- matrix rich (\>15%) - wackes
169
name three fine grained siliciclastic rocks.
**fine grained siliciclastic rocks**
mudstones
siltstones
shales
170
what is meant by fissility?
fissility - a tendency to split along thin bedding planes or laminae, which mudstones and siltstones do not have.
171
describe shales.
**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
whats the difference between shale and slate?
**shale** - splits along bedding planes
**slate** - splits on cleavage planes
173
what is meant by textural and mineralogical maturity in sedimentary rocks?
**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.
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what are carbonates?
**carbonates**
are biogenic minerals
sometimes inorganic precipitats from carbonate saurated waters
common in warm, high productivity seas (near the equator)
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describe the classification of carbonates.
where do teh names dolostone and dolomitic limestone come from?
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**
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name and describe three carbonate facies.
**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.
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many siliclastic rocks cotain carbonates as _________ and \_\_\_\_\_\_\_\_
many siliclastic rocks contain carboantes as fossils (bioclasts) and as crystalline cement (spar)
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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.
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**
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what are calcirudites, calarenites, and calcilutites?
**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)
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useing the folk classification of limestones
what are the four prefixes and the surffix when cemented by sparite and a micritic matrix.
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.
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what are the four main allochem types?
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.**
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what are pisoliths?
pisoliths are ooids bounded together
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what are ooids?
concentric
nucleus, skeletal fragment or quartz grain.
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what is the dunham classifying system based on?
the dunham classifying system is based on the presence of mud matrix and grain/ mud support
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what are the five classifications of the dunham system. describe them.
**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.
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what are evaporites?
**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
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explain how evaporite minerals form.
**evaporite minerals**
minerals precipitate out in definite order:
least soluable first (carbonates)
then gypsum
followed by halite
then the K/Mg salts
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to what depths and temperatures does metamorphism happen to?
up to 35km
200 - 700 degrees
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what are the two types of metamorphism?
**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
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what effects the mineralogy of metamorphic rocks?
temperature
pressure
source rock
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whats the difference between calcite, shale, and basalt as they are metamorphosed?
calcite will usually recrystallise
shale and basalt will go under different mineralogical changes.
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what do metamorphic facies help us to define?
metamorphic facies help us to define the conditions of temperature and/or pressure
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what are metamorphic facies defined by?
metamorphic facies are defined by the **rock texture** (foliation, granularity, etc) and **new mineral growth**
194
what are isograds?
**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
what is foliation?
**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
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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?
slate
phyllite
schist
gneiss
splitting surfaces is low grade coaser grade foliation, distinct banding is higher grade.
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describe slates.
**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
describe phyllite
slightly higher grade than slate
often **foliation planes**
**glossy sheen** due to presence of larger crystals of micas and chlorites than in slates.
199
descirbe schists
**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
describe gneisses
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
name three non-foliated metamorphic rocks.
hornfels (spotted hornfels)
quartzites
marbles
202
what is meant by granoblastic texture?
metamorphic rocks show uniform crystal size
203
describe schistosity
wavy foliation, parallel mica growth, often with porphyroblasts of garnet
204
describe hornfels
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
describe quartzite
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
describe marbles
**metamorphosed limestone**
equi-granular interlocking recrystallised calcite crystals with no foliation.
can form under **regional and contact** metamorphism
207
what is contact metamorphism?
what controls its extent?
baking of a country rock by igneous intrusions
extent is controlled by size of the body. **larger intrusions** create an **aureole** surrounding the intrusion
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