1.1 Minerals Flashcards
1
Q
What are minerals?
A
Substances with a definite chemical composition and atomic structure and formed by the inorganic processes of nature
2
Q
What are minerals composed of?
A
Elements
3
Q
What are the eight most common elements found in minerals?
A
- oxygen
- aluminium
- calcium
- potassium
- silicon
- iron
- sodium
- magnesium
4
Q
What is the name of the mineral made from pure silica?
A
Quartz
5
Q
What is the symbol for pure silica/quartz?
A
SiO2
6
Q
What are the physical properties of minerals that are studied?
A
- colour
- streak
- lustre
- form or habit
- cleavage
- fracture
- hardness
- relative density
7
Q
What are the chemical properties of minerals that are studied?
A
- acid test
* taste test
8
Q
What does the colour of a mineral depend on?
A
The colours of the spectrum that it reflects
9
Q
What does it mean, in terms of reflection of light, if a mineral is colourless?
A
It allows most light to pass through it
10
Q
What is the name of a colourless quartz?
A
Rock crystal
11
Q
What is the name of a purple quartz?
A
Amythyst
12
Q
What is the name of a yellow quartz?
A
Citrine
13
Q
What is the name of a brown quartz?
A
Smoky quartz
14
Q
What is the name of a pink quartz?
A
Rose quartz
15
Q
What is the name of a white quartz?
A
Milky quartz
16
Q
What is the streak of a mineral?
A
The colour of a mineral’s powder
17
Q
How is the streak of a mineral seen?
A
By rubbing it on a piece of unglazed porcelain (streak plate)
18
Q
Is the colour of a mineral’s streak necessarily the same as its normal colour?
A
No
19
Q
What colour streak does black haematite have?
A
Red
20
Q
What happens if minerals are harder than the streak plate?
A
They will have no streak
21
Q
What is the lustre of a mineral?
A
The amount and quality of light that it reflects
22
Q
What terms can be used to describe lustre?
A
- metallic
- vitreous (glassy)
- adamantine
- dull
23
Q
What is a metallic lustre?
A
The ordinary lustre of metals
24
Q
What is a vitreous lustre?
A
The lustre of broken glass
25
What is an adamantine lustre?
The brilliant lustre of diamond
26
What is a dull lustre?
Having little or no lustre
27
What is the form or habit of a mineral?
The common shape a mineral takes
28
What terms are used to describe crystal structure?
* crystallised
* crystalline
* cryptocrystalline
* amorphous
29
What does it mean if a mineral is crystallised?
The mineral occurs as well developed crystals
30
What does it mean if a mineral is crystalline?
A confused mixture of imperfect crystals
31
What does it mean if a mineral is cryptocrystalline?
Mere traces of crystalline structure
32
What does it mean if a mineral is amorphous?
No crystalline structure - this is quite rare
33
What is the crystal structure of peridot?
Crystallised
34
What is the crystal structure of fluorite?
Crystalline
35
What is the crystal structure of gypsum?
Cryptocrystalline
36
What is the crystal structure of graphite?
Amorphous
37
What are other common shapes among minerals (not crystalline, crystallised etc.)?
* cubic
* rhombic
* hexagonal
* reniform (kidney shaped)
* nodular
* columnar
* fibrous
* foliated
38
What does it mean if a mineral is nodular?
Detached, rounded masses
39
What does it mean if a mineral is foliated?
Thin layers or lamellae
40
What is the cleavage of a mineral?
The tendency to split along definite planes, known as cleavage planes
41
What direction are cleavage planes in?
Parallel to crystal forms
42
How is cleavage described?
Good/poor
43
Types of cleavage?
* cubic cleavage - 3 directions
* rhombohedral - 3 directions
* basal cleavage - 1 direction
44
What is fracture?
The irregular way in which a mineral breaks apart
45
What are the 3 main types of fracture?
* uneven - rough surface
* hackly
* conchoidal
46
What is hackly fracture?
A surface studded with sharp and jagged elevations
47
What is conchoidal fracture?
Concave or convex surface with concentric lines (like a shell)
48
What scale is used to test hardness?
Moh's scale
49
What does it mean if you can scratch a mineral with your fingernail?
It has hardness of less than 2.5
50
What does it mean if you can scratch a mineral with a copper coin?
It has a hardness between 3.5 and 2.5
51
What does it mean if you can scratch a mineral with a steel pin?
It has a hardness between 3.5 and 5.5
52
What does it mean if you can't scratch a mineral with a steel pin?
It has hardness more than 5.5
53
What is the relative density of a mineral?
Shows the number of times heavier that mineral is than an equal volume of water
54
How to calculate relative density?
Mass of specimen in air (g) / water displaced by specimen (cm3)
55
What is the commonly used test for calcite?
Acid test
56
What is the most important mineral in limestone?
Calcite
57
How is an acid test carried out?
Dilute HCl dropped on the mineral, which bubbles and gives of CO2
58
What is the taste test used to identify?
Halite
59
Why is halite salty?
Composed of NaCl
60
How can minerals be formed?
* crystallisation from a melt
* metamorphic crystallisation
* crystallisation from solution in evaporating water
* crystallisation as a cement from flowing pore waters
* crystallisation from hydrothermal fluids
61
What type of rocks does crystallisation from a melt generally apply to?
Igneous rocks
62
How does crystallisation from a melt form minerals?
Minerals crystallise when magma cools to form igneous rocks
63
What happens when magma cools very rapidly?
Volcanic glass is formed
64
When will big crystals form?
When magma deep in the crust cools slowly
65
When will small crystals form?
When magma that pours out onto the surface of the crust cools rapidly
66
When will both big and small crystals form?
When magma cooling partly deep in the crust and partly on the surface
67
What minerals does granite contain?
* mica
* quartz
* feldspar
68
When does metamorphism occur?
When rocks are changed by an increase in temperature and/or pressure
69
Does metamorphism involve a liquid phase?
No - it is a change from one solid to another
70
Which minerals are formed by crystallisation from a melt?
* quartz
* mica
* feldspar
* olivine
* augite
71
Which minerals are formed by metamorphic recrystallisation?
* calcite
| * garnet
72
Which minerals are formed by crystallisation from solution in evaporating water?
Halite
73
Which minerals are formed by crystallisation as cement from flowing pore waters?
* quartz
| * calcite
74
Which minerals are formed by crystallisation from hydrothermal fluids?
gangue minerals:
* quartz
* calcite
ore minerals:
* haematite
* galena
75
In metamorphic recrystallisation, what does higher temperatures mean for crystal size?
Larger crystals
76
In metamorphic recrystallisation, what do higher pressures mean for crystal size?
Produce layering in the rock - foliation
77
What is evaporite?
Substances left behind from evaporation
78
When does a solution become saturated?
When it is heated by the sun
79
How is halite formed?
* minerals carried into lake in solution
* sun heats up lake waters
* evaporation of lake waters
* halite precipitated out from solution
80
How are minerals formed by crystallisation as a cement from flowing pore waters?
* when sediment deposited it will only become hard sedimentary rock if it is cemented by minerals
* water in pores between sediments carries dissolved minerals which are precipitated out between clasts
* minerals bind clasts together form the cement of the rock
81
What are the three main minerals that form cements in sedimentary rocks?
* stiperstones conglomerate - quartz
* wenlock limestone - calcite
* navajo sandstone - haematite
82
What is haematite also known as?
Iron oxide
83
Where are hydrothermal minerals deposited from?
Hot water solutions
84
How do hydrothermal minerals form?
From the heated waters given off by magma as it cools - these hot waters can dissolve and carry metals
85
What are the deposits of metallic minerals called?
Ores
86
When hot water solutions are cooled, how can the elements crystallise?
* in cavities or fissures as hydrothermal veins
| * in between the grains of sediments as impregnations
87
What are gangue minerals?
The minerals in hydrothermal veins that are not ores and not of any value e.g. quartz and calcite
88
What happens when some minerals form at higher temperatures in hydrothermal veins?
This causes the vein to show the minerals as zones
89
How are minerals in sedimentary rocks most often found?
As clasts (grains)
90
Which characteristics of clasts in sedimentary rocks can determine how much transportation and erosion has taken place?
* size - given by the length of its long axis
* sorting - how close clasts are to being the same size
* roundness
* sphericity
91
What are the three main methods of prospecting for minerals?
* field mapping
* geophysical techniques
* geochemical techniques
92
What is field mapping?
Involves analysing geology of an area in a field, producing a field map and therefore suggested locations for mineral exploitation
93
What are the geophysical techniques of prospecting?
* magnetic surveys
* seismic surveys
* electrical surveys
94
What are magnetic surveys?
Using a magnetometer, ore bodies are picked out as they show a stronger magnetism as they are more able to take on the earth's magnetic field
95
What are seismic surveys?
Using seisometers, they discover mineral reserves but are more widely used in the petroleum industry
96
What are electric surveys?
Ore bodies conduct an electric current more easily than other geological materials - a resistivity survey involves passing current through the crust to show location of ore body
97
What are the geochemical techniques of prospecting?
* soil and sediment sampling
| * water sampling
98
How can soil and sediment sampling prospect minerals?
Soil and sediment are formed from breakdown of rock, so may contain evidence of ore bodies that lie beneath the surface
99
How can water sampling prospect minerals?
Water may contain small amounts of metallic elements that indicate water has passed over an ore body
100
What are the problems with prospecting using water sampling?
Water can be contaminated because concentrations of metals are low, and variations in acidity make interpretation difficult
101
What are the methods used to mine minerals?
* mining hydrothermal veins
* mining large ore bodies
* mining evaporite deposits
102
How are hydrothermal veins mined?
Using the adit and stope method
103
What is the adit and stope method of mining?
* adit - tunnel driven into hillside at a low angle to get to vein
* stope - tunnel dug along line of veins
* stope and adits join to create complex of tunnels in the mine
104
How can ore minerals be extracted when found in large bodies?
By the process of open cast mining - only for when ore is near the surface. Remove overlying rock.
105
How can halite be mined from evaporite?
When found near surface, use pillar and stall method
106
What is the pillar and stall method of mining in evaporite deposits?
Removing most of halite but leaving pillars so support roof of mine`
107
Why is halite good for the pillar and stall method of mining?
It does not fracture, behaves in a plastic manner
