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University First Year > Week 4: How to build a planet: minerals and rocks > Flashcards

Week 4: How to build a planet: minerals and rocks Flashcards

1
Q

What is a mineral?

A

-naturally occurring chemical substance
-has a definite atomic structure and chemical formula (specific chemical composition)
-crystalline, solid inorganic materials

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2
Q

What are the key physical properties of minerals, that can be used in their identification? What controls these properties?

A

All controlled by theri chemical composition
1. Colour= determined by chemical composition
2. Lustre= surface appearance
3. Hardness= strong chemical bonds result in hard minerals
4. Habit: the shape it takes
5. Cleavage= planes of weakness in mineral related to atomic structure
6. Fracture= tendency to break along irregular surfaces other than cleavage planes
7. Density= depends on atomic weight of atoms/ions and their closeness of packing

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3
Q

Silicate minerals you should be familiar with:

A

-quartz
-feldspar
-mica
-pyroxene
-amphibole
-olivine
-clay minerals
-garnet

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4
Q

Non-silicate minerals you should be familiar with:

A

-calcite
-dolomite
-gypsum
-halite
-magnetite
-pyrite
-hematite

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5
Q

What four mechanisms result in the formation of minerals?

A
  1. Cooling and crystallisation
  2. Evaporation and precipitation
    3.Sold state transformation
  3. Secretion by organisms
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6
Q

How are minerals grouped according to their chemical composition?

A
  1. Silicates= contain O and Si e.g. quartz (SiO2)
  2. Carbonates= contain C and O e.g. calcite (CaCO3)
  3. Oxides= contain O and metallic cations e.g. hematite (Fe2O3)
  4. Sulfides= contain S (but no O) and metallic cations e.g. pyrite (FeS2)
  5. Sulfates= contain S04 and metallic cations e.g. anhydrite (CaSO4)
  6. Halides= contain one of CI, F, I or Br (but no O)
  7. Hydroxides= contain OH
  8. Native elements= metals occurring as a single element, not in combination e.g. gold, silver, copper
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7
Q

What is quantitatively the most common group of minerals in the Earth’s crust?

A

Silicates

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8
Q

What is the building block of all silicate minerals?

A

Silicate tetrahedra- ploymerisation

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9
Q

How do the arrangement of the tetrahedra affect the structure of silicate minerals, and what are common mineral examples of each type?

A
  1. Islands= isolated tetrahedra, do not share any oxygens e.g Olivine and Garnet
  2. Single Chains= two of the three basal oxygens are bonded together (Si:O= 1:3) e.g. Pyroxene
  3. Double chains= two single chains that share oxygens where tetrahedra touch to form a double chain (Si:O= 2:7) e.g. amphibole
  4. Sheets= share 3 oygens along the base of the tetrahedra to form 2D sheets (Si:O= 2:5) e.g mica
  5. 3D Frameworks= all oxygens are shared between adjacent tetrahedra to form 3D framework (Si:O= 1:2) e.g quartz and feldspar
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10
Q

What is fractional crystallisation and how does it control the silicate mineral formed?

A
  • minerals crystallize from a melt at diffrent temperatures
    -as they crystallize they change chemical composition of remaining melt
    -from mafic to felsic
    (known as Bowens reaction series)
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11
Q

What is a rock?

A

-aggregate of mineral grains (or in some cases non-mineral solid matter e.g. glass, fossils)
-naturally occurring
-solid
-can be either crystalline or cemented
-can be very strong and durable
-some rocks are more resistant to weathering than others

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12
Q

How are rocks classified? What are the three common types of rocks?

A

Rocks are classified by their origin
1.Igneous
2. Sedimentary
3. Metamorphic

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13
Q

What is the main difference between igneous, sedimentary and metamorphic rocks in terms of their origins?

A
  1. Igneous rock= solidification from molten rock
  2. Sedimentary rocks= erosion and deposition of pre-existing rocks
  3. Metamorphic rocks= changes due to heat and/or pressure
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14
Q

How can texture be used to distinguish igneous, sedimentary and metamorphic rocks?

A
  1. Igneous= crystalline
  2. Sedimentary= non-crystalline and layered (layering due to grain size)
  3. Metamorphic=crystalline and layered (layering due to composition
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15
Q

What are the most common minerals found in igneous, metamorphic and sedimentary rocks?

A
  1. Igneous:
    -quartz
    -feldspar
    -mica
    -pyroxene
    -amphibole
    -olivine
  2. Sedimentary:
    -quartz
    -clay minerals
    -feldspar
    -calcite
    -dolomite
    -gypsum
    -halite
  3. Metamorphic:
    -quartz
    -feldspar
    -mica
    -garnet
    -pyroxene
    -staurolite
    -kyanite
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16
Q

How do intrusive and extrusive igneous rocks form?

A

Intrusive= trapped, cooled and solidified beneath the surface
Extrusive= erupted from a volcano and cooled at Earth’s surface (lavas and ashes)

17
Q

How are igneous rocks classified?

A

By their texture
Granite= coarse-grained/slow cooling
Basalt= fine grained/fast cooling

18
Q

What controls the texture of an igneous rock?

A

Granite= coarse grained slow cooling
Basalt= fine grained fast cooling

19
Q

What is meant by mafic and felsic? What minerals do these rocks contain? (igneous)

A

felsic:
-rich in silica, low in Mg
(quartz, feldspar, muscovite)

mafic:
-poor in silica, rich in Mg
(biotite, amphibole, pyroxene, olivine)

20
Q

Where are igneous rocks found?

A

areas of high tectonic activity

21
Q

What is a clastic sedimentary rock? How is grain size used to name a clastic rock?

A

Clastic= (detrital)
-allochthonous
-physical processes

22
Q

How does weathering affect the minerals present in a clastic sedimentary rock compared to the parent igneous or metamorphic rock?

A

Feldspar:
igneous/metamorphic= 60%
sedimentary= 15%

Quartz:
igneous/metamorphic= 25%
sedimentary= 50%

Ca, Mg/Fe silicates:
igneous/metamorphic= 15%
sedimentary= 0%

23
Q

How do evaporites and limestones form? (sedimentary)

A

Evaporites formed due to evaporation of a saline lake

24
Q

Why has the composition of limestones changed through time? (sedimentary)

A

due to changes in deposition of carbonates over geological time

25
Q

What is diagenesis and lithification? (sedimentary)

A

Diagenesis= processes occurring during lithification
Lithification= conversion of sediment to rock

26
Q

Where are sedimentary rocks found?

A

deposited as layers of sediment in land or in water

27
Q

What is metamorphism? How does it cause rocks to change?

A

changed by the action of heat and or pressure
can cause minerals to recrystallize e.g limestone to marble

28
Q

What is metamorphic grade? How does a mudstone change as metamorphic grade increases?

A

as pressure and heat increases chemical reactions occur changing mudstone into migmatite (from low grade to high grade)

29
Q

Where does metamorphism take place?

A

continental crust

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