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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
What shapes can crystals be for an orthorhombic system?
dipyramid Rectangular or cubic prism
26
What will the axes and angles be like for a monoclinic system?
Axes all different lengths Angles- a and c intercept at 90* b doesnt
27
What are some examples of minerals with monoclinic systems?
orthorclase feldspar diopside Staurolite
28
What are the axes and angles like for a triclinic system?
three axes all different lengths No axes meet at 90*
29
What are some examples of minerals with triclinic systems?
plagioclase feldspar Microcline feldspar
30
What will the axes and angles be like in a hexagonal system?
4 axis 3 of which are equal length Vertical c-axis intersects shorter axis at 90*short axis 120*
31
What minerals have hexagonal systems?
apatite beryl
32
What crystal shapes can hexagonal systems form?
Hexagonal prism Hexagonal dipyramid
33
What are the axes and angles like in a trigonal subsystem?
4 axis 3 equal in length Vertical c-axis intercepts short at 90* short intercept a 120*
34
How does a trigonal system vary from a hexagonal system?
it has a 3 fold axis of rotational symmetry instead as principal axis of 6
35
What minerals have a trigonal system?
Quartz Calcite
36
What shape can crystals in a trigonal system form?
dipyramid Rhombohedron scalenohedron
37
What is crystal system not the same as?
atomic organisation (chain or double chain silicate)
38
What will determine the crystal system?
structural organisation of elements on a repeating scale
39
Is shape of crystal and unit cell shape identical?
no but the shape will be controlled by fundamental symmetry of underlying unit cell
40
What is a crystal habit?
the characteristic external shape of an individual crystal or crystal group
41
What does the exact shape of crystals come down to?
growth of different faces
42
What is crystal twinning?
during crystal growth where intergrowth of two parts of a crystal are related by a symmetry element (twin)
43
What can a crystal twin take the form of?
mirror plane rotation axis inversion about a point
44
What will crystal twinning look like in a plagioclase feldspar?
zebra pattern of successive twinned parallel plates
45
How can minerals with the exact same chemistry exist in different structural organisations?
stability and formation dependent on temperature and pressure
46
What factors can be used to describe and identify crystals/minerals?
Colour Lustre Streak Hardness Cleavage Fractures Habit
47
What is the problem with using colour to identify crystals?
translucent or transparent crystals can vary widely in colour
48
What is an example of where using colour to identify a crystal would be trickier?
quartz can vary from colourless to to white to yellow to grey to pink to purple to black
49
What can lead to colour variations of crystals?
minor (ppb) impurities and defects
50
What is lustre?
appearance of mineral when light is reflected from its surface?
51
What terms can be used to describe lustre?
Metallic Waxy Earthy Pearly Vitreous
52
What is streak? (used for mineral identification)
colour of mineral in powder form (may or may not be same colour as mineral)
53
What type of mineral is streak must useful with?
minerals with metallic or earthy lustre
54
How do you obtain the streak from a mineral?
scratch mineral onto white porcelain (steak plate)
55
What is the hardness of a mineral?
resistance of a mineral to scratching or abrasion by other materials
56
How is hardness determined?
scratching sample with known hardness material or mineral
57
How is hardness recorded?
Mohs hardness scale
58
How does the Mohs hardness scale work?
10 minerals ranked in ascending order of hardness with diamond at number 10 (hardest)
59
What is cleavage with minerals?
way in which a mineral breaks is determined by the arrangement of atoms and strength of chemical bonds holding them together
60
What does a mineral which exhibits cleavage do?
consistently breaks/cleaves along flat parallel surfaces (cleavage planes)
61
How can cleavage quality be described?
Perfect Good Poor
62
What are fractures when describing minerals?
when a mineral only breaks by fracture along random irregular surfaces
63
How can habit be used to identify minerals?
this is the external shape of individual crystals which relates to underlying crystal system and how well developed growth faces are
64
What types of lustre ore there?
Metallic Earth vitreous waxy pearly
65
What is the description of a metallic lustre?
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
What is the description of an earthy lustre?
looks like earth, or dirt. Like metallic minerals these are completely opaque, but dull
67
What is the description of a vitreous lustre?
like that of glass, shiny and translucent to transparent
68
What is the description of a waxy lustre?
looks like paraffin, typically translucent but dull
69
What pearly lustre?
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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