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Mcgill Geology > Week 2 > Flashcards

Week 2 Flashcards

1
Q

how many minerals are known

A

almost 6000 (5327 officially)

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2
Q

why study minerals

A

minerals are the building blocks of the body of our planet
- minerals make up all of the rocks and sediments on earth

minerals are important to humans
- industrial minerals (manufacturing)
- ore minerals (metals)
-gem minerals (human passions)

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3
Q

what is a mineral

A

geologic definition:
- naturally occuring
- formed geologically
-solid
-crystalline structure
-most minerals are inorganic

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4
Q

can we synthesize minerals

A

yes: sapphire, diamond, quartz

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5
Q

how are minerals formed by geologic processes

A

mostly formed by geologic processes
- freezing from a melt (like volcanic magmas)
- precipitation from a dissolved state in water or other solvent
- chemical reactions at high pressures and temperatures

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6
Q

how are minerals formed by biogenically

A

living organisms can create minerals
- vertebrate bones
- oyster mussel and clam shells
- skeletal types
- tooth enamel

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7
Q

how are minals formed

A
  • mostly geologic processes and also by living organisms ( biogenically)
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8
Q

what is a crystalline structure

A

a state of matter that can maintain its shape indefinitely

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9
Q

minerals can be melted or vapourized but they are not ….

A

liquids or gases..

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10
Q

how are mineral defined?

A

by their structure butthey have a definite elemental composition

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11
Q

minerals can be defined by a chemical formula but more commonly they are defined by

A

as a structure

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12
Q

what are the different structures of a mineral

A

simple ( largely defined by a chemical formula)

complex (many elements might be substituted)

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13
Q

what is a crystal

A
  • single continuous piece of crystalline solid
  • typically bounded by flat surfaces (crystal faces)
  • crystal faces grow naturally as the minral forms
  • crystals are sometimes prized mineral specimens
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14
Q

T or F crystals come in a variety of different shapes

A

T

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15
Q

what makes a crystal so special

A
  • regular geometric from
  • crystals interact with light to create attractive beauty
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16
Q

what is X-ray diffraction used for

A

study and identify minerals

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17
Q

how does X-ray diffraction worl

A
  • X-ray beam passed through a crystal or crystal powder creates distinctive pattern
  • diffraction pattern related to arrangement of atoms in crystal
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18
Q

what do you see when you look inside a crystal

A
  • ordere atomic patterns in minerals display symmetry
  • ordered atoms like tiny balls packed together
  • held in place by chemical bonds
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19
Q

symmetry characterisitcs are used to what

A

identify minerals

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20
Q

what are the displays of symmetry in crystals

A
  • mirror images
  • rotation about an axis (or axes)
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21
Q

what defines the crystal structure q

A

the way atoms are packed

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22
Q

what do the physical propreties (hardness, shape) depend upon

A
  • identity of atoms
  • arrangement of atoms
  • nature of atomic bonds
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23
Q

what does the nature of atomic bonds control caracteristics of crystals (chemical) ex:

A

ex: - diamond and graphite are both made of Carbon

  • diamond: atoms arranged in tetrahedra: hardest mineral
  • graphite: atoms arranged in sheets: softest mineral
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24
Q

five ways minerals can form

A
  • solidification from a melt
  • precipitation from a solution
  • solid-state diffusion
  • biomineralization
  • precipitating directly from a gas
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25
Q

fullerines and graphene

A
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26
Q

Solidification from a melt

A
  • crystals grow when the melt cools
  • liquid freezes to form solid
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27
Q

precipitation from a solution

A

seeds form when a solution becomes saturated

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28
Q

what are garnets

A

garnets are fundamentally a structure rather than a stoichiometric chemical composition as in molecules (reddish minerals)

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29
Q

what are the various compositions that the structure of the garnet can be formed with

A

X3Y2 (SiO4)

X is occupied by divalent cations (Ca, Mg, Fe, Mn)2+

Y is occupied by trivalent cations (Al, Fe, Cr)3+

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30
Q

mineral growth is often restricted by what

A

lack of space

ex: anhedral: grown in tight space, no cystal faces
Ex: euhedral: grown in an open cavity, good crystal faces

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31
Q

what is much more prevalent: anhedral or euhedral

A

anhedral

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32
Q

where do euhedral crystals grow

A

in the open space in a geode

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33
Q

how can minerals be destroyed ( cant destroy the chemistry)

A
  • melting: heat breaks the bonds holding atoms together
  • dissolving: solvents (moslty water) break atomic bonds
  • chemical reaction: reactive materials break bonds
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34
Q

name some easily seen properties for mineral identification

A

color
crystal shape

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35
Q

some properties require handling or testing

A
  • hardness
  • magnetization
  • specific gravity
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36
Q

common propreties

A
  • color
  • streak on ceramic tile
  • luster
  • hardness
  • specific gravity
  • crystal habit
  • fracture or cleavage
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37
Q

color of minerals

A

part of visible light that is not absorbed by a minerla

  • disgnostic for some minerals (ex: malachite is distinctive green)
  • some mineras exhibit a borad color range ex: quartz
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38
Q

what does color varities reflect

A

trace impurities

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39
Q

what is streak

A

color of a powder produced by crushing mineral

obtained by scraping a mineral on unglazed porcelain

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40
Q

luster

A

the way a mineral surface scatters light

  • metallic
    -nonmetallic: silky, glassy,satiny, resinous, pearly, earthy
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41
Q

hardness

A

sscratching resistance of a mineral

derives from the strength of atomic bonds

hardness compared the Mohs scale for hardness

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42
Q

Mohs scale for hardness

A

fingernail: Gypsum
Copper penny: Calcite
Glass: Apatite
Stell File: Orthoclase

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43
Q

what does specific gravity represent

A

the density of a mineral: mineral weight over the weight of an equal water volume

(how heavy it feels)

ex: Galena feels heavier than quartz

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44
Q

crystal habbit

A

-a single crystal with well-fromed faces,
or
- an aggregate of many well-fromed crystals

  • arrangement of faces reflects internal atomic structure
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45
Q

variation in directional growth rates

A

blocky or equand (equal growth rate in 3D

  • bladed (shaped like knofe blade)
  • needle-like: rapid growth in one dimension, slow in others
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46
Q

special physical propreties

A
  • effervescence (reactivity with acid ex: calcite)
  • magnetism (ex: magnetite0
  • taste: (lick test ex: halite (salt))
47
Q

fracture

A

mineral breaks in ways that reflect atomic bonding

48
Q

what does fracturing imply

A

equal bond strength in all directions

ex: quartz displays conchoidal fracture

  • break like glasss (smooth cruved surfaces)
  • shard edges
49
Q

cleavage

A

tendency to break along planes of weaker atomic bonds

50
Q

what does cleavage produce in a mineral

A

flat and shiny surfaces

51
Q

how is cleavage described

A

by the number of planes and their angles

52
Q

T or F: crystal faces only occur on external surfaces and often forms parallel steps

A

T

53
Q

Exemple of cleavage

A
  • one direction (micas)
  • two directions at 90º (ex pyroxene)
  • two directions not at 90º (ex amphibole)
  • three directions at 90º (ex: halite)
  • three directions not at 90º (ex: calcite)
54
Q

mineral classification: seperated how?

A
  • the principal anion (negative ion)
    OR
  • anionic group (negative molecule)
55
Q

what is the most abundant mineral class

A

silicates

56
Q

Minerals are classified by their dominant anion

A
  • silicates (SiO24-) are colled rock forming minerals
  • constitute almost the entire crust and mantle of Earth
  • they are the most common mineral
    ex: quartz
57
Q

mineral classes: - Oxides

A
  • Metal Cations (FE2+, Fe3+, Ti2+) are bonded by oxygen
  • ex: magnetite (Fe3O4), Rutile (TiO2), Hematite (fe2O3)
58
Q

mineral classes: Sulfides (S)

A
  • metal cations are bonded to a suflide anion

ex: - pyrite (FeS2)
- Galena (PbS)
- (sphalerite ZnS)

59
Q

mineral classes: Sulfates (SO42-)

A

metal cation bonded to a sulfate anionic group
- many sulfates form by evaporation of seawater
- ex: Gypsum (CaSO4 X 2H2O) , Anhydrite (CaSO4)

60
Q

mineral class: by their dominan anion: Halides (CL- or F-)

A

ex: halite (NaCl)
- Fluorite (CaF2)

61
Q

mineral class: dominant anion: Carbonates (CO32-)

A

ex: Calcite (CaCO3)
Dolomite (Ca,Mg)(CO3)
Natrite (Na2CO3)

62
Q

mineral class: minerals with no (dominant) anion: native metlas

A

common: (Cu, Au, Ag)

  • ex: :Copper (Cu)
  • gold (Au)
  • Silver (Ag)

pure masses of single metal or alloy

63
Q

where do silicate minerals dominate eath

A

mantle and crust

64
Q

what are silicate minerals made out of

A

made of oxygen and silicon with other atoms

65
Q

what is the anionic unit of SiO44- (silicate_

A

silicon-oxygen tetrahedron

  • four O atoms are bonded to a central Si atom
  • Define the corners of a four-sided geometric figure
  • the “silica tetrahdron” is the building block of silicates
66
Q

Independent Tetrahedra

A
  • silica tetrahedra share no oxygens
  • linked by cations
  • ex: olivine, Garnet
67
Q

Single Chains

A

silica tetrahedra link to share two oxygens
- ex: pyroxenes

68
Q

double chains

A

silica tetrahedra alternate sharing two and three oxygens
- ex: amphiboles

69
Q

sheet silicates

A
  • silica tetrahedra share three oxygens
  • create 2D flat sheets of linked tetrahedra
  • characterized by one direction of perfect cleavage
  • ex: micas, clays
70
Q

Framework silicates

A

all four oxygens in each silica tetrahedron are shared
- ex: feldspars, silica (quartz) group

71
Q

what is a gemstone

A

a mineral with special value
- rare: fromed by unusual geological processes
- beautiful: strikingly unique colour, clarity, luster

72
Q

what is a gem

A

a cut and polished stone created for jewelry

  • precious: stones that are particularly rare and expensive (ex: diamond, ruby)
  • semiprecious: less rare (ex: topaz, garnet)
73
Q

T or F gemstone facets are not natural crystal faces

A

True

74
Q

where do diamonds come from

A

originate under extremely high pressure (150 km deep in the upper mantle) where pure carbon is compressed into the diamond structure

  • rifting causes deep-mantle rock to move upward
  • diamonds are found in kimberlite pipes
75
Q

what is a volcano

A

a vent where molten rock comes out of earth

76
Q

what happens when a volcano errupts

A
  • hot basaltic lava pools around volcanic vent
  • hot, syrupy lava runs downhill as a lava flow
  • the lava flow slows, loses heat, crusts over
  • flow stops and cools, forming igneous rock
77
Q

how is igneous rock formed

A

by cooling from a melt

78
Q

difference between magma and lava

A

magma: melted rock below ground
- lava: melted rock once it has reached the surface

79
Q

what temp does igneous rock freeze at

A

high temp: 1100 to 650 degrees

80
Q

different types of igneous rock

A
  • extrusive igneous rock and intrusive igneous rock
81
Q

extrusive igneous rocks

A
  • cool quickly at the surface (above ground)
  • lava flows, streams or mounds of cooled melt
  • pyroclastic debris: cooled framgents
  • volcanic ash: fine particles of volcanic glass
  • volcanic rock: fragmented by eruption
82
Q

intrusive igneous rocks

A

cool below the ground
- much greater volume than extrusive igneous rocks
- cooling rate is slower than extrusives (large colume magma chamber, smaller volume tabular bodies or columns)

83
Q

why does magma form?

A
  • magma is not eveywhere below earth’s crust
  • magma only forms in special tectonic conditions
84
Q

what are the special tectonic conditions that magma forms in

A
  • partial melting occurs in the crust and upper mantle
  • magma is fluid-like rather thatn solid
  • melting is caused by: pressure release, volatile addition, heat transfer
85
Q

what are the causes of melting

A
  • decrease in pressure (decompression)
  • addition of volatiles ( lfux melting)
  • heat transfer melting
86
Q

decrease in pressure (P) decrompression (cause of melt)

A
  • the base of the crust is hot enough to melt mantle rock
  • due to high Pressure, rock deosnt melt
  • melting will occur if pressure decreases
87
Q

when does the pressure drop (melting of rock)

A

drops when hot rock is carried to shaller depths
- matnle plumes
- beneath rifts
-beneath mid-ocean ridges

88
Q

addition of volatiles (cause of melting)

A
  • volatiles lower the melting Temperature of a hot rock
  • common volatiles include H2O and CO2
  • subduction carries water into the mantle, melting rock
89
Q

heat transfer melting (cause of melting)

A

-rising magma carries mantle heat with it
- this raises the T in nearby crustal rock, which then melts

90
Q

what is magma made of?

A

magmas have three componens ( solid, liquid, gas)
- solid: solidified mineral crystals are carried inthe melt
- liquid: the melt itself is composed of mobile ions (majority Si and O, lesser Al, Ca, Fe, Mg, Na, K)
- different mixes of elements yield different magmas
-gas: variable amounts of dissolved gas occur in magma: dry magma (scarce volatiles) wet magma (15% volatiles ex: H2O)

91
Q

types of magma

A

based on % of silica (SiO2)
- felsic (feldspar and silica 66-76%)

  • intermediate (52-66%)
  • mafic (Mg and Fe rich) (45-52% SiO2)
  • ultramafic (38-45% SiO2)
92
Q

why are there different magma compositions?

A

magma vary chemically
- source rock dictates initioal magma composition
- initial source rock compositions
-partial melting
-assimilation
-magma mixing

93
Q

Partial melting

A
  • upon melting, rocks rarely dissolve uniformly
  • portion of rock melts instead: Si rich minerals melt first then Si poor minerals melt last
  • partial melting yields a silica-rich magma
94
Q

source rock dictates initioal magma composition ex:

A
  • mantle source: ultra-mafic and mafic magmas
  • crustal surface: mafic, intermediate, and felsic magmas
95
Q

partial melting yields what type of magma

A

partial melting yields a silica-rich magma

96
Q

what happens when you remove the partial melt from its source what is created

A
  • felsic magmas form granites and rhyolites
  • mafic magmas form basalts and gabbros
97
Q

assimilation

A

magma melts the wall rock it passes through
- blocks of wall rock fall into magma
- assimilation of these rocks alters magma composition

98
Q

magma mixing

A
  • different magmas may blend in a magma chamber
  • result combines the characteristics of the two
  • often magma mixing is incomplete, resulting in blobs of one rock type suspended within the otehr
99
Q

how does magma move

A

it tends to rise upward:
- magma may move upward in the curst
- may breach the surface: volcano

100
Q

what does magma movement do

A

transfers mass from deep to shallow parts of earth:
- crucial process in the earth system
- provides the raw material for soil, atmosphere and ocean

101
Q

why does magma rise

A
  • it is less dense than surrounding rocks: (magma = more buoyant, which lifts it upward)
  • weight of overlying rock creates pressure ( pressure squeezes magma upward)
102
Q

what is the speed of magma movement and what does it depend on

A

the speed of magma flow is governed by viscosity

103
Q

what does a lower viscosity do to magma dlow

A

eases movement

104
Q

how is a lower viscosity magma generated

A
  • higher T
  • lower SiO2 content
  • higher volatile content
105
Q

temperature does what (viscosity of magma)

A

hot= lower viscosity
cooler = higher viscosity

106
Q

volatile content (viscosity)

A

more volatiles = lower visc.

less volatiels = higher viscosity

107
Q

silica content (viscosity)

A

less SiO2 ( mafic) ; lower viscosity

more SiO2 (felsic): higher viscosity

108
Q

how fast does magma cool what does it depend on

A
  • depth (depth is hotter, shallow is cooler)
    -shape (spherical bodies cool slowly, tabular faster)
  • groundwater: circulatin water removes heat
109
Q

why d0es depth change cooling rate?

A

deep plutons lose heat very slowly: take long time to cool
- shallow flows lose heat more rapidly: cool quickly

110
Q

how are igneous rocks changed

A
  • changes with cooling:

fractional crystallization: early crystals settle by gravity

Melt composition changes as a result: Fe, Mg, Ca are removed as early mafic minerals settle out, remaining melt becomes enriched in Si, Al , Na and. K

111
Q

what does Bowen’s REaction Series do?

A

divsed experiments cooling melts:

  • early crystal settle out, (removing Fe, Mg, Ca)
  • remaining melt progressively enriched in Si, Al, Na
112
Q

what did Bowen discover

A

minerals solidify in a specific series:
- continuous: plagioclase change from Ca rish to Na rich

  • discontinuous: minerals start and stop crystallizing
113
Q

ex of discontinuous minerals

A

olive
pyroxene
amphibole
biotite

114
Q
A

Mcgill Geology (5 decks)

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