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Geology A Level OCR > 1.1 Rocks and minerals > Flashcards

1.1 Rocks and minerals Flashcards

1
Q

Define the term: mineral

A

A naturally occurring chemical substance having a definite composition and crystalline structure.

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2
Q

Define the term: rock

A

An aggregate or mixture of one or more minerals.

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3
Q

Define the term: crystal

A

A solid with plane faces formed when atoms are arranged in a structurally ordered pattern.

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4
Q

What is the chemical formula for quartz?

A

SiO₂

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5
Q

What is the chemical formula for calcite?

A

CaCO₃

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6
Q

What is the chemical formula for pyrite?

A

FeS₂

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7
Q

What is the chemical formula for galena?

A

PbS

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8
Q

What is the chemical formula for native sulphur?

A

S

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9
Q

What is the chemical formula for native copper?

A

Cu

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10
Q

What is the name of the mineral with the chemical formula FeS₂?

A

pyrite

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11
Q

What is the name of the mineral with the chemical formula CaCO₃?

A

calcite

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12
Q

What is the name of the mineral with the chemical formula SiO₂?

A

quartz

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13
Q

What is the name of the mineral with the chemical formula S?

A

native sulfur

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14
Q

What is the mineral with the chemical formula PbS?

A

galena

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15
Q

What is the mineral with the chemical formula Cu?

A

native copper

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16
Q

Define the term: lustre

A

The surface appearance of a mineral, as it interacts with light

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17
Q

What is sublimation? How does it relate to crystal formation?

A

Sublimation is the transition of a substance directly from the gas phase to the solid phase, or the reverse, without passing through the intermediate liquid phase.

Native sulphur crystals sometimes form by sublimation around volcanic vents.

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18
Q

Define the term: glass

A

An amorphous solid with no crystalline structure.

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19
Q

Define the term: grain boundary

A

The line of contact between mineral crystals in a rock.

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20
Q

What is the most common element in the Earth’s crust?

A

oxygen

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21
Q

What is the second most common element in the Earth’s crust?

A

silicon

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22
Q

How do natural glasses form?

A

Very rapid cooling of a liquid - the disorganised arrangement of the liquid is ‘frozen’.

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23
Q

What is obsidian?

A

A natural glass formed of silicon and oxygen atoms.

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24
Q

Why is glass not a rock or mineral?

A

It is not a mineral because there is no organised crystalline structure.

It is not a rock because it is not composed of one or more minerals.

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25
Q

How do mineral crystals grow?

A

Mineral crystals grow outwards from the centre by adding to their faces.

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26
Q

Why are the angles between the faces of a given mineral constant?

A

The angle between the faces is a result of the regular arrangement of the atoms in their structure.

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27
Q

Why do larger crystals form when a liquid is cooled more slowly?

A

Fewer crystals begin to form if a liquid is cooled more slowly. This smaller number of crystals have more space into which they can grow.

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28
Q

Why are the grain boundaries between crystals in a rock often irregular?

A

The crystals will grow until they meet each other, so they fill all available space.

Crystals that grow into a cavity will have good crystal shape.

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29
Q

Why is colour not always a useful diagnostic characteristic of a mineral?

A

Some minerals can occur in several different colours.

30
Q

Which minerals can be distinguished by colour?

A

The two micas can be distinguished by colour - muscovite is pale grey and biotite is black

31
Q

How is a streak test performed?

A

A mineral specimen is scraped across the surface of a piece of unglazed porcelain known as a streak plate.

32
Q

What is the streak of a mineral?

A

Streak is the colour of the powder left by the mineral when a streak test is performed.

33
Q

Why is the streak test not useful for distinguishing between silicate minerals?

A

Most silicates have a white streak, which does not help to distinguish between them.

34
Q

What colour is galena’s streak?

A

lead-grey

35
Q

What colour is the streak for iron pyrite?

A

black (although pyrite is brassy yellow)

36
Q

Why do some minerals not leave a streak?

A

If the mineral is harder than the streak plate, it will not make a powder.

37
Q

What is meant by the term earthy lustre?

A

The mineral has a dull, rough surface.

38
Q

What is meant by the term adamantine lustre?

A

The mineral shines like a diamond.

39
Q

What is the technical word for a ‘glassy’ lustre?

A

vitreous

40
Q

What does the term crystal habit mean?

A

the shape of the crystal: cubic, hexagonal, etc.

41
Q

What shape are quartz crystals?

A

hexagonal

42
Q

Which mineral is characterised by a twinning crystal habit?

A

feldspars (particularly K-feldspar/plagioclase feldspar)

43
Q

Define the term: cleavage

A

Cleavage refers to the planes of weakness in the atomic structure of crystals.

44
Q

Which mineral group have perfect cleavage in one direction (planar)?

A

micas (sheet silicates)

45
Q

Describe the cleavage of calcite.

A

Calcite has three cleavage directions which are not at right angles.

46
Q

What is meant by the term fracture when applied to minerals?

A

Minerals that break along irregular surfaces tend to fracture. They do not have cleavage because the bonds between the atoms are strong.

47
Q

What is meant by the term conchoidal fracture?

A

Conchoidal fracture refers to the fracture of a mineral in a series of concentric curved cracks - like a broken glass bottle.

48
Q

Which scale is used to measure mineral hardness?

A

Mohs scale of hardness

49
Q

What is the maximum value on Mohs scale of hardness?

A

10

50
Q

State the reference minerals for Mohs scale, in order from soft to hard.

A

Talc, Gypsum, Calcite, Fluorite, Apatite, Feldspar, Quartz, Topaz, Corundum, Diamond

51
Q

What is the hardness of quartz?

A

7

52
Q

What is the hardness of diamond?

A

10

53
Q

What is the hardness of calcite?

A

3

54
Q

How could you distinguish between quartz and calcite, if you did not have any HCl acid?

A

quartz (7) is harder than calcite (3)

55
Q

What are the units for density?

A

grams per cubic centimetre ( g cm -3 )

56
Q

Define the term: specific gravity

A

Specific gravity is the ratio of the mass of a mineral compared with the mass of an equal volume of water.

It provides the same figures as density expressed in g cm-3 but as it is a ratio there are no units.

57
Q

What is the specific gravity of quartz if it has a density of 2.65 g cm-3?

A

2.65

58
Q

What is the diagnostic test for carbonate minerals such as calcite (CaCO3)?

A

carbonate minerals react strongly with dilute HCl acid - they effervesce (produce bubbles of CO2)

59
Q

What is the density of water?

A

1 g cm-3

60
Q

How can you calculate the specific gravity of a mineral sample, if given the volume of water displaced by the sample?

A

Divide the mass of the specimen by the mass of the water it displaces.

20 cm-3 of water has a mass of 20 g

61
Q

What are the diagnostic characteristics of quartz?

A

hardness 7

no streak

no cleavage / irregular fracture

62
Q

What are the diagnostic characteristics of feldspar?

A

cleavage in two directions

white streak

approximately rectangular habit

hardness 6

63
Q

What are the diagnostic characteristics of mica?

A

good cleavage in one direction

hardness 2.5-3

64
Q

What are the diagnostic characteristics of augite (most common pyroxene)?

A

square or eight-sided habit in cross-section

two directions of cleavage (93°)

dark green to black

65
Q

What are the diagnostic characteristics of hornblende (most common amphibole)?

A

diamond shaped in cross-section

two directions of cleavage (c. 60°)

green to black

66
Q

What are the diagnostic characteristics of olivine?

A

rounded shape

poor cleavage / conchoidal fracture

hardness 6.5-7

67
Q

What are the diagnostic characteristics of calcite?

A

reacts with dilute HCl acid

rhombic crystal habit with three cleavage planes (or irregular)

hardness 3

68
Q

What are the diagnostic characteristics of garnet?

A

rounded or six-sided in cross-section

hardness 6 - 7.5

no cleavage / poor conchoidal fracture

deep red to brown colour

69
Q

What are the diagnostic characteristics of kyanite?

A

flat or blade crystal habit

two directions of cleavage

70
Q

If you observe pink crystals in an igneous rock, which mineral are they most likely to be?

A

feldspar (particularly orthoclase feldspar)

71
Q

If you observe white crystals in a dark-coloured igneous rock, what mineral is it most likely to be?

A

feldspar (usually plagioclase/K-feldspar)

Geology A Level OCR (23 decks)

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