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Geology A Level OCR > 1.1 Rocks and minerals > Flashcards

1.1 Rocks and minerals Flashcards

(71 cards)

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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
How do mineral crystals grow?
Mineral crystals grow **outwards from the centre** by adding to their **faces**.
26
Why are the **angles** between the **faces** of a given mineral constant?
The angle between the faces is a result of the **regular arrangement of the atoms** in their structure.
27
Why do larger crystals form when a liquid is cooled more slowly?
**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.
28
Why are the **grain boundaries** between crystals in a rock often **irregular**?
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.
29
Why is **colour** not always a useful **diagnostic** characteristic of a mineral?
Some minerals can occur in several different colours.
30
Which minerals can be distinguished by **colour**?
The two **micas** can be distinguished by colour - **muscovite** is **pale grey** and **biotite** is **black**
31
How is a **streak** test performed?
A mineral specimen is scraped across the surface of a piece of unglazed porcelain known as a **streak plate**.
32
What is the **streak** of a mineral?
Streak is the **colour** of the **powder** left by the mineral when a streak test is performed.
33
Why is the **streak test** not useful for distinguishing between **silicate** minerals?
Most silicates have a **white** streak, which does not help to distinguish between them.
34
What colour is **galena**'s **streak**?
lead-grey
35
What colour is the **streak** for **iron pyrite**?
**black** (although pyrite is brassy yellow)
36
Why do some minerals **not** leave a **streak**?
If the mineral is **harder** than the streak plate, it will not make a powder.
37
What is meant by the term **earthy lustre**?
The mineral has a dull, rough surface.
38
What is meant by the term **adamantine lustre**?
The mineral shines like a diamond.
39
What is the technical word for a ‘**glassy**’ **lustre**?
vitreous
40
What does the term **crystal habit** mean?
the shape of the crystal: cubic, hexagonal, etc.
41
What shape are quartz crystals?
hexagonal
42
Which mineral is characterised by a **twinning** crystal habit?
**feldspars** (particularly K-feldspar/plagioclase feldspar)
43
Define the term: **cleavage**
Cleavage refers to the **planes of weakness** in the **atomic structure** of crystals.
44
Which mineral group have **perfect** cleavage in **one direction** (planar)?
**micas** (sheet silicates)
45
Describe the cleavage of **calcite**.
Calcite has **three** cleavage directions which are **not at right angles**.
46
What is meant by the term **fracture** when applied to minerals?
Minerals that break along irregular surfaces tend to **fracture**. They do not have **cleavage** because the bonds between the atoms are strong.
47
What is meant by the term **conchoidal fracture**?
Conchoidal fracture refers to the fracture of a mineral in a series of concentric curved cracks - like a broken glass bottle.
48
Which scale is used to measure mineral **hardness**?
Mohs scale of hardness
49
What is the maximum value on **Mohs scale of hardness**?
10
50
State the **reference** minerals for **Mohs** scale, in order from **soft** to **hard**.
**T**alc, **G**ypsum, **C**alcite, **F**luorite, **A**patite, **F**eldspar, **Q**uartz, **T**opaz, **C**orundum, **D**iamond
51
What is the hardness of **quartz**?
7
52
What is the hardness of **diamond**?
10
53
What is the hardness of **calcite**?
3
54
How could you distinguish between **quartz** and **calcite**, if you did not have any HCl acid?
quartz (7) is harder than calcite (3)
55
What are the units for **density**?
grams per cubic centimetre ( g cm -3 )
56
Define the term: **specific gravity**
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
What is the **specific gravity** of quartz if it has a density of 2.65 g cm-3?
2.65
58
What is the diagnostic test for carbonate minerals such as **calcite** (Ca**CO3**)?
carbonate minerals react strongly with dilute HCl acid - they **effervesce** (produce bubbles of CO2)
59
What is the density of **water**?
1 g cm-3
60
How can you **calculate** the **specific gravity** of a mineral sample, if given the volume of water displaced by the sample?
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
What are the diagnostic characteristics of **quartz**?
hardness 7 no streak no cleavage / irregular fracture
62
What are the diagnostic characteristics of **feldspar**?
cleavage in two directions white streak approximately rectangular habit hardness 6
63
What are the diagnostic characteristics of **mica**?
good cleavage in one direction hardness 2.5-3
64
What are the diagnostic characteristics of **augite** (most common **pyroxene**)?
square or eight-sided habit in cross-section two directions of cleavage (93°) dark green to black
65
What are the diagnostic characteristics of **hornblende** (most common **amphibole**)?
diamond shaped in cross-section two directions of cleavage (c. 60°) green to black
66
What are the diagnostic characteristics of **olivine**?
rounded shape poor cleavage / conchoidal fracture hardness 6.5-7
67
What are the diagnostic characteristics of **calcite**?
reacts with dilute HCl acid rhombic crystal habit with three cleavage planes (or irregular) hardness 3
68
What are the diagnostic characteristics of **garnet**?
rounded or six-sided in cross-section hardness 6 - 7.5 no cleavage / poor conchoidal fracture deep red to brown colour
69
What are the diagnostic characteristics of **kyanite**?
flat or blade crystal habit two directions of cleavage
70
If you observe pink crystals in an igneous rock, which mineral are they most likely to be?
**feldspar** (particularly orthoclase feldspar)
71
If you observe white crystals in a dark-coloured igneous rock, what mineral is it most likely to be?
**feldspar** (usually plagioclase/K-feldspar)

Geology A Level OCR (23 decks)

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