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Atoms to volcanoes - 33739 > Crystal systems and mineral describing > Flashcards

Crystal systems and mineral describing Flashcards

1
Q

What will not be the case in olivine with silicon and oxygen bond?

A

oxygen linked to each silicon not directly connected to another silicon bonded oxygen

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2
Q

What affects whether an ion can be accommodated by a structure?

A

charge
ionic radius

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3
Q

What is a unit cell? (crystal structure)

A

smallest repeating unit

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4
Q

What way can unit cell be be defined by?

A

Three axes
Three angles

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5
Q

What are the axes/angles for unit cell?

A

A B C
specific lengths
(C longest axis)
Angles will be in between the axes

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6
Q

What is the simplest structure that can be defined by unit cell?

A

a cube

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7
Q

What is another name for the cubic system?

A

isometric system

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8
Q

What will the symmetry of angles be like in systems with varying axes lengths?

A

less symmetry

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9
Q

What is an orthorhombic structure?

A

A B C axes are different lengths but angles are still at 90*

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10
Q

What is an example of an orthorhombic structure?

A

orthopyroxene

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11
Q

How many crystal systems are there?

A

6

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12
Q

What three factors define which system forms?

A

how many axes it has
length of axes
angle at which axes meet

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13
Q

What are the 6 crystal systems?

A

simple cubic
tetragonal
orthorhombic
monoclinic
triclinic
Hexagonal family (hexagonal and trigonal)

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14
Q

What will the axes and angles be like in a cubic system?

A

Axes - all same length
Angles- all intersect at 90*

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15
Q

Are cubic systems simple?

A

No
means it has high symmetry and structure consistent in all directions

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16
Q

What does isotropic mean?

A

properties are identical in all directions

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17
Q

What are some examples of minerals with cubic systems?

A

Garnet
Diamond
Gold

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18
Q

What shapes can crystals in the cubic system create?

A

cube
octahedron
dodecahedron

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19
Q

What are the axes and angles like in a tetragonal system?

A

3 axes C is longer than A & B
angles all intersect at 90*

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20
Q

What is the unit cell in a tetragonal system?

A

rectangular prism

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21
Q

What are some examples of minerals that have a tetragonal system?

A

rutile
zircon

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22
Q

What shapes can crystals in the tetragonal system create?

A

tetragonal prism
Dipyramid
Pyramid with prism

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23
Q

What are the axes and angles like in an orthorhombic system?

A

Axes all different lengths
Angles all intersect at 90*

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24
Q

What minerals have an orthorhombic system?

A

andaulsite
enstatite
olivine

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25
Q

What shapes can crystals be for an orthorhombic system?

A

dipyramid
Rectangular or cubic prism

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26
Q

What will the axes and angles be like for a monoclinic system?

A

Axes all different lengths
Angles- a and c intercept at 90* b doesnt

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27
Q

What are some examples of minerals with monoclinic systems?

A

orthorclase feldspar
diopside
Staurolite

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28
Q

What are the axes and angles like for a triclinic system?

A

three axes all different lengths
No axes meet at 90*

29
Q

What are some examples of minerals with triclinic systems?

A

plagioclase feldspar
Microcline feldspar

30
Q

What will the axes and angles be like in a hexagonal system?

A

4 axis 3 of which are equal length
Vertical c-axis intersects shorter axis at 90short axis 120

31
Q

What minerals have hexagonal systems?

A

apatite
beryl

32
Q

What crystal shapes can hexagonal systems form?

A

Hexagonal prism
Hexagonal dipyramid

33
Q

What are the axes and angles like in a trigonal subsystem?

A

4 axis 3 equal in length
Vertical c-axis intercepts short at 90* short intercept a 120*

34
Q

How does a trigonal system vary from a hexagonal system?

A

it has a 3 fold axis of rotational symmetry instead as principal axis of 6

35
Q

What minerals have a trigonal system?

A

Quartz
Calcite

36
Q

What shape can crystals in a trigonal system form?

A

dipyramid
Rhombohedron
scalenohedron

37
Q

What is crystal system not the same as?

A

atomic organisation (chain or double chain silicate)

38
Q

What will determine the crystal system?

A

structural organisation of elements on a repeating scale

39
Q

Is shape of crystal and unit cell shape identical?

A

no but the shape will be controlled by fundamental symmetry of underlying unit cell

40
Q

What is a crystal habit?

A

the characteristic external shape of an individual crystal or crystal group

41
Q

What does the exact shape of crystals come down to?

A

growth of different faces

42
Q

What is crystal twinning?

A

during crystal growth where intergrowth of two parts of a crystal are related by a symmetry element (twin)

43
Q

What can a crystal twin take the form of?

A

mirror plane
rotation axis
inversion about a point

44
Q

What will crystal twinning look like in a plagioclase feldspar?

A

zebra pattern of successive twinned parallel plates

45
Q

How can minerals with the exact same chemistry exist in different structural organisations?

A

stability and formation dependent on temperature and pressure

46
Q

What factors can be used to describe and identify crystals/minerals?

A

Colour
Lustre
Streak
Hardness
Cleavage
Fractures
Habit

47
Q

What is the problem with using colour to identify crystals?

A

translucent or transparent crystals can vary widely in colour

48
Q

What is an example of where using colour to identify a crystal would be trickier?

A

quartz can vary from colourless to to white to yellow to grey to pink to purple to black

49
Q

What can lead to colour variations of crystals?

A

minor (ppb) impurities and defects

50
Q

What is lustre?

A

appearance of mineral when light is reflected from its surface?

51
Q

What terms can be used to describe lustre?

A

Metallic
Waxy
Earthy
Pearly
Vitreous

52
Q

What is streak? (used for mineral identification)

A

colour of mineral in powder form (may or may not be same colour as mineral)

53
Q

What type of mineral is streak must useful with?

A

minerals with metallic or earthy lustre

54
Q

How do you obtain the streak from a mineral?

A

scratch mineral onto white porcelain (steak plate)

55
Q

What is the hardness of a mineral?

A

resistance of a mineral to scratching or abrasion by other materials

56
Q

How is hardness determined?

A

scratching sample with known hardness material or mineral

57
Q

How is hardness recorded?

A

Mohs hardness scale

58
Q

How does the Mohs hardness scale work?

A

10 minerals ranked in ascending order of hardness with diamond at number 10 (hardest)

59
Q

What is cleavage with minerals?

A

way in which a mineral breaks is determined by the arrangement of atoms and strength of chemical bonds holding them together

60
Q

What does a mineral which exhibits cleavage do?

A

consistently breaks/cleaves along flat parallel surfaces (cleavage planes)

61
Q

How can cleavage quality be described?

A

Perfect
Good
Poor

62
Q

What are fractures when describing minerals?

A

when a mineral only breaks by fracture along random irregular surfaces

63
Q

How can habit be used to identify minerals?

A

this is the external shape of individual crystals which relates to underlying crystal system and how well developed growth faces are

64
Q

What types of lustre ore there?

A

Metallic
Earth
vitreous
waxy
pearly

65
Q

What is the description of a metallic lustre?

A

looks like a metal, such as steel or copper, in being both shiny and opaque, even
when looking at a thin edge. Many metallic minerals become dull or earthy when they are exposed to the elements for a long time

66
Q

What is the description of an earthy lustre?

A

looks like earth, or dirt. Like metallic minerals these are completely opaque, but dull

67
Q

What is the description of a vitreous lustre?

A

like that of glass, shiny and translucent to transparent

68
Q

What is the description of a waxy lustre?

A

looks like paraffin, typically translucent but dull

69
Q

What pearly lustre?

A

has an appearance similar to a pearl – translucent and shiny but with a bit of light
refraction, producing a rainbow effect on the surface

Atoms to volcanoes - 33739 (16 decks)

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