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Geology, LEC 172 > Minerals, Lectures 4 & 5 > Flashcards

Minerals, Lectures 4 & 5 Flashcards

1
Q

Minerals

A

Naturally occurring, inorganic crystalline solids.

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2
Q

Are minerals elements, atoms or compounds

A

elements or compounds

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3
Q

Crystalline

A

regular internal structure

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4
Q

Rocks make up…

A

rocks,

they are the building blocks of rocks

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5
Q

Rocks

A

naturally occurring solid aggregates of minerals

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6
Q

Main rock forming minerals

A

silicates

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7
Q

What do sillicates contain?

A

Si and O, combined with metallic elements

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8
Q

Example of a silicate mineral?

A

quartz

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9
Q

Two most abundant elements in the Earth’s crusts

A

silicon and oxygen

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10
Q

How do minerals form?

A

by crystallisation

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11
Q

Non-silicate minerals

6

A
  1. magnetite
  2. haematite
  3. pyrite
  4. gypsum
  5. calcite
  6. halite
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12
Q

Building block of silicate minerals

A

silica tetrahedron - SiO4

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13
Q

Third most abundant element in the Earth’s crust

A

Aluminium

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14
Q

How do silica tetrahedron made up minerals?

A

arranged in various ways with cations in the interstices

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15
Q

Four constituent minerals of granite

A

quartz
biotite (mica)
plagioclase feldspar
orthoclase feldspar

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16
Q

Crystal faces

A

The natural, flat (planar) boundaries of crystals.

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17
Q

If plenty of space how do crystal faces form?

A

slowly

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18
Q

If space is limited, how do crystals grow?

A

grow over and coalesce to become a solid mass of crystalline particles/grains - results in few or no grains showing crystal faces

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19
Q

Mineral solid solutions

A

Cations of similar sizes substitute for each other and make mixed compounds.

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20
Q

Example of a solid solutions

A

olivine

21
Q

Solid solution: olivine, what is it made up of?

A

Fe and Mg

22
Q

Pure Fe olivine

A

pure Fe olivine: Fe2SiO4

Fayalite

23
Q

Pure Mg olivine?

A

pure Mg olivine: Mg2SiO4

Forsterite

24
Q

Natural olivines are …

A

intermediate between foresterite and fayalite

25
Q

What do all major silicate groups (except quartz) show?

A

some degree of solid solution

26
Q

Natural glass

A

obsidian, volcanic glass

27
Q

How does natural glass form?

A

Forms when lava cools too quickly to form crystals.

28
Q

Structure of natural glass

A

Atoms are arranged in silica tetrahedra but, instead of being linked in a regular manner, they are randomly arranged as they would be in a liquid.

29
Q

What are the layers in obsedian?

A

gas bubbles

30
Q

Characteristics of obsedian
colour
3

A

jet-black
glassy (vitreous) lustre
shiney

31
Q 
Characteristics of obsedian
shape
crystals?
rock or mineral or neither?
4
A

conchoidal (smoothly curved) fracture
lack, or have very small crystals
may have vesicles (bubbles) and flow bands
not a rock or mineral

32
Q

Polymorphism

A

When chemical substances form more than one kind of crystal structure: different structures are called polymorphs

33
Q

Example of polymorphism
CaCO3
which conditions for one of the polymorphs?

A

calcite
and
aragonite (higher density, stable at higher pressures)

34
Q

What can calcite and aragonite make up?

A

shelly, invertebrate organisms such as foraminifera, clams and corals

35
Q

Example of polymorphism
carbon
naturally occurring polymorphs

A

graphite and diamond

36
Q

Example of polymorphism
carbon
not naturally occurring

A

fullerenes and graphene

37
Q

Which naturally occurring carbon polymorph is more stable at higher pressures and has a higher density?

A

diamond

38
Q

A mineral has…

A

a narrowly defined chemical composition and characteristics physical properties

39
Q

Example of a characteristics physical property of a mineral?

A

hardness

40
Q

Microscopy

A

the study of samples under the microscope

41
Q

Petrography

A

the detailed description of rocks

42
Q

What is used to see small minerals within rocks?

A

a polarising (petrographic) microscope and thin section (rock slices 0.03mm thick)

43
Q

How are the minerals in rocks viewed under a polarising/petrographic microscope?

A
  • rocks and mienrals become transparent if sliced thinly

- the microscope passes polarised light through

44
Q

Polarised light

A

light vibrating in only one plane

45
Q

Polariser

A

optical filter converts beam of light of mixed polarisation into beam with well defined polarisation

46
Q

Two main ways of examining thin sections under a microscope

A

PPL and XPL

47
Q

XPL

A

cross polarised light

48
Q

PPL

A

plane polarised light

49
Q

Pleochroism

A

An optical phenomenon in which a mineral appears to be a different colour when observed at different angles. different angle = different colour

Geology, LEC 172 (6 decks)

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