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BIOS1013 - Environmental Geoscience > Lecture 2 - Minerals > Flashcards

Lecture 2 - Minerals Flashcards

1
Q

What are minerals?

A

Minerals are naturally formed inorganic solids that have a specific chemical composition and a distinct crystalline structure.

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2
Q

What are the properties of minerals determined by?

A

Their composition and crystal structure.

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3
Q

What is composition?

A

The chemical elements that make up a mineral and the proportions in which they are present.

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4
Q

What is crystal structure?

A

The organised way in which the atoms of the element are packed together in a mineral.

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5
Q

What are solids that have a crystal structure called?

A

Crystalline.

All minerals are crystalline.

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6
Q

What is a crystal?

A

Any solid body that grows with planar surfaces.

The angle between faces in any crystalline structure remains constant and this reflects the ordering of atoms in the structure.

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7
Q

What is the growth habit?

A

The characteristic crystal form of each mineral.

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8
Q

What are the five types of growth habit?

A

Prismatic

Cubic

Acicular

Botryoidal

Fibrous

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9
Q

What do prismatic growth crystals look like?

A

A prism with planar sides.

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10
Q

What do cubic growth crystals look like?

A

Cubes.

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11
Q

What do acicular growth crystals look like?

A

Needles.

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12
Q

What do botryoidal growth crystals look like?

A

A bunch of grapes.

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13
Q

What do fibrous growth crystals look like?

A

Thin spindly fibres.

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14
Q

What is a conchoidal fracture?

A

A fracture with smooth, curved surfaces that resembles the inside of a seashell.

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15
Q

What are minerals composed of?

A

Some of composed of a single element.

However, most minerals are compounds.

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16
Q

What is the structure of galena (PbS)?

A

It forms a giant ionic lattice structure.

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17
Q

What is the structure of diamond?

A

Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral structure.

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18
Q

What is the structure of graphite?

A

Hexagonal layers of carbon atoms covalently bonded to three other carbon atoms.

Between the layers, there are weak van der Waals forces holding the structure together.

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19
Q

What is cleavage?

A

The tendency for a mineral to break in a preferred direction along bright, reflective planar surfaces.

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20
Q

What are the directions along which cleavage occurs governed by?

A

The crystal structure of the mineral.

The cleavage plane will be along where the bonding between atoms is relatively weak.

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21
Q

What shape crystals does fluorite (CaF₂) form when it fractures?

A

Octahedrons.

This is because it breaks along four planar directions.

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22
Q

What shape does muscovite break into?

A

Sheets of minerals.

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23
Q

What shape does K-Feldspar break into?

A

Cuboids as there are two, perpendicular cleavage planes.

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24
Q

What shape does halite (NaCl) break into?

A

Cuboids are there are 3 cleavage planes.

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25
Q

What is lustre?

A

The quality and intensity of light reflected from a mineral.

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26
Q

What are five lustres?

A

Metallic

Vitreous

Resinous

Pearly

Greasy

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27
Q

What is a metallic lustre?

A

It has the appearance of a polished metal surface.

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28
Q

What is a vitreous lustre?

A

It has a glassy appearance.

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29
Q

What is a resinous lustre?

A

It has the look of dried glue or amber.

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30
Q

What is a pearly lustre?

A

It looks like a pearl and can appear powdery.

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31
Q

What is a greasy lustre?

A

It looks like the surface is covered by a film of oil.

32
Q

What is the colour of a mineral dictated by?

A

The chemical composition.

However, it cannot be accurately used to identify minerals as the colour is often caused by impurities.

33
Q

What is a streak?

A

The colour of a thin layer of powdered material left when a mineral is rubbed on an unglazed ceramic plate.

34
Q

Is streak more reliable than colour?

A

Yes, streak is more reliable for identifying a mineral.

35
Q

What is the colour and streak of haematite (Fe₂O₃)?

A

Black with an opaque metallic lustre.

Streak is red.

36
Q

What is hardness?

A

A mineral’s relative resistance to scratching.

It is a function of the crystal structure and the strength of the bonds between atoms.

37
Q

What scale is used to measure hardness?

A

The Mohs relative hardness scale.

It is a scale from 1 to 10 (1 being talc and 10 being diamond).

38
Q

Where are the three common objects placed on the Mohs scale?

A

Fingernail (between 2 and 3)

Copper penny (between 3 and 4)

Pocket knife / glass (between 5 and 6)

39
Q

What is specific gravity?

A

A ratio of weight equal to the weight of a substance in air divided by the weight of an equal volume of pure water.

40
Q

What other properties can be used to identify minerals?

A

Magnetism

Taste

Chemical reaction with acid

Double refraction

Fluorescence

41
Q

What are megascopic textural features of rocks?

A

Features that can be observed with the naked eye.

42
Q

What are microscopic textural features?

A

Features that can only be viewed at a high magnification.

43
Q

What type of light is better for viewing minerals under a microscope?

A

Polarised light.

44
Q

What is the composition of the Earth’s crust?

A

45.2% Oxygen

27.2% Silicon

8% Aluminium

5.8% Iron

5.06% Calcium

45
Q

What are the three main mineral groups?

A

Silicates (the most abundant)

Carbonates, sulphates and phosphates

Ore minerals (oxides and sulphides).

46
Q

What is the chemical formula for a silicate?

A

SiO₄⁴⁻

47
Q

What are the chemical formulae for carbonates, sulphates and phosphates?

A

CO₃²⁻

SO₄²⁻

PO₄³⁻

48
Q

What are the chemical formulae for oxides and sulphides?

A

O²⁻ and S²⁻.

49
Q

What is the structure of a silicate tetrahedron?

A

A tetrahedron with silicon at the centre with four oxygen atoms covalently bonded.

The silicon atom has a 4+ charge and the oxygen atoms have a 2- charge which results in an overall 4- charge.

50
Q

What reactions can the silicate anion take part in?

A

It can form an ionic bond with another atom.

It can form covalent bonds between tetrahedra so that they share oxygen atoms.

51
Q

Where can silicate tetrahedra share oxygen atoms?

A

At one of the oxygen atoms.

52
Q

What are island silicates?

A

The tetrahedra are isolated through oxygen bonding to cations such as Mg2+ or Fe2+.

53
Q

What rocks have island silicate bonding?

A

Olivine and garnet.

54
Q

Where is olivine found?

A

It is a common constituent of igneous rocks in oceanic crust and the upper part of the mantle.

55
Q

What are the two types of chain silicates?

A

Pyroxenes and Amphiboles

56
Q

What is a pyroxene?

A

A single chain of silicate anions.

Its formula is (SiO₃)²ⁿ⁻

57
Q

What are amphiboles?

A

Double chains of silicate anions.

Its formula is (Si₄O₁₁)⁶ⁿ⁻

58
Q

What is an example of a pyroxene and an amphibole?

A

Pyroxene - augite.

Amphibole - hornblende.

59
Q

What are the features of pyroxenes and amphiboles?

A

They are dark colours.

They are common in igneous rocks.

They are difficult to distinguish apart from looking at their cleavage.

60
Q

What is the difference in cleavage between pyroxenes and amphiboles?

A

Pyroxenes have 2 cleavages at 90°.

Amphiboles have 2 cleavages at 120°.

61
Q

What are sheet silicates?

A

Each tetrahedron shares three oxygen atoms. The sheets are connected by cations.

Micas are sheet silicates.

62
Q

What happens when kaolinite adsorbs water?

A

Water adsorbs between the polymerised sheets making it wet, weak, slippery and easily moulded.

63
Q

What percentage of all minerals in the continental crust are feldspar?

A

60% of all minerals.

64
Q

What are the two common types of feldspar?

A

Potassium feldspar

Plagioclase feldspar.

65
Q

How is the feldspar group created?

A

All oxygen atoms in the silicate tetrahedron are shared.

Al substitutes for Si.

66
Q

Where is the feldspar group found?

A

It is abundant in sea-floor rocks.

67
Q

What are the features of quartz, SiO₂?

A

Quartz forms six sided crystals and are found in many colours.

The colours occur due to impurities in the crystal.

Fine grained forms of quartz are called chalcedony.

68
Q

What are three common carbonate minerals?

A

Calcite - CaCO₃

Dolomite - CaMg(CO₃)₂

Aragonite - CaCO₃

69
Q

Which carbonate mineral reacts with hydrochloric acid?

A

Calcite.

70
Q

What are two common forms of the sulphate anions?

A

Anhydrite (CaSO₄)

Gypsum (CaSO₄.2H₂O)

71
Q

What is gypsum used for?

A

It is the raw material used for making plaster.

72
Q

What is the most important phosphate mineral?

A

Apatite.

73
Q

Why is apatite the most important phosphate mineral?

A

Bones and teeth are made of it and it is a common mineral in many igneous and sedimentary rocks.

It is the main source of phosphate fertiliser.

74
Q

What are the features of sulphides?

A

They have metallic lustres and high specific gravities.

75
Q

What are common sulphides?

A

Pyrite - FeS₂

Galena - PbS

Sphalerite - ZnS

76
Q

What are the two most common oxide minerals?

A

Magnetite - Fe₃O₄

Haematite - Fe₂O₃

77
Q

What can minerals tell us about?

A

The temperature and pressure of where they formed.

The climate present.

The composition of seawater by studying evaporite minerals.

BIOS1013 - Environmental Geoscience (8 decks)

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