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FoG > FoG1 - Mineralogy > Flashcards

FoG1 - Mineralogy Flashcards

1
Q

what structure has no bridging oxygens + net charge of 4- per cation

A

orthosilicate (isolated tetrahedra)

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2
Q

example of orthosilicate

A

olivine, garnet, zircon

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3
Q

what structure has one bridging oxygen per cation and a net charge of 2- per cation

A

chain silicate

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4
Q

example of chain silicate

A

pyroxene

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5
Q

how do chain silicates charge balance

A

layer 2 chain silicates with edge sharing octahedra layer in between (2+ cations)

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6
Q

what structure has net charge on cation of 1.5- and 5/4 bridging oxygens

A

double chain silicate

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7
Q

example of double chain silicate

A

amphibole

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8
Q

Why can double chain silicates fit large cations in its structure

A

irregular octahedra leave large holes in structure

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9
Q

how do double chain silicates charge balance

A

layer of octahedra between 2 double chain silicate layers

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10
Q

what structure has 3/2 bridging oxygens and a net charge of 1- per cation

A

sheet silicate

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11
Q

how do sheet silicates charge balance

A

have 2+ or 1+ cations in gaps in structure

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12
Q

what structure has 4 bridging oxygens and a neutral charge per cation

A

3d framework

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13
Q

example of 3d framework silicate

A

quartz

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14
Q

example of sheet silicate

A

mica (biotite)

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15
Q

what is the structure of feldspars

A

Al3+ replace Si4+ in framework structure, and additional cations fill gaps in structure, achieving charge neutrality

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16
Q

what structure has 3 cations

A

triangular

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17
Q

what structure has 4 cations

A

tetrahedra

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18
Q

what structure has 6 cations

A

octahedral

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19
Q

what structure has 8 cations

A

cubic

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20
Q

what structure has 12 cations

A

cuboctohedral

21
Q

end members of olivine

A

forsterite = Mg
fayalite = Fe

22
Q

types of garnet

A

pyralspite series = have Al3+
ugrandite series = have Ca2+

23
Q

name 3 polymorphs pf aluminosilicate (Al2 SiO5)

A

kyanite
andalusite
sillimanite

24
Q

P-T of andalusite

A

low temp

25
Q

P-T of sillimanite

A

high temp high pressure

26
Q

P-T of kyanite

A

high pressure

27
Q

why are zircons so good for dating

A

U4+ easily substitutes into crystal structure, but Pb2+ cannot. Therefore any Pb in the structure must have come from decay

28
Q

solid solution for pyroxenes

A

Enstatite = Mg (SiO3)
Ferrosilite = Fe (SiO3)

29
Q

solid solution for pyroxenes with 50% Calcium

A

Diopside = CaMg (Si2O6)
Hedenbergite = CaFe (Si2O6)

30
Q

pyroxenes with ~50:50 Mg:Fe and varying Calcium

A

Pigeonite = some Ca
Augite = less than 50% Ca

31
Q

name of pyroxenes with <5% Ca

A

Orthopyroxene

32
Q

name of pyroxene with 5-50% Ca

A

Clinopyroxene

33
Q

general amphibole

A

Hornblende

34
Q

physical characteristics of phyllosilicates

A

platy, layered, planar, layered structure
flexible, soft as weak bonds between layers

35
Q

what do most phyllosilicates have at centre of hexagons

A

-OH group (water)

36
Q

2 ways of arranging octahedra in a sheet

A

tri-octahedral = all 3 sites occupied, 2+ cations
di-octahedral = 2 / 3 sites occupied, 3+ cations

37
Q

types of layering sheet silicates

A

1:1 = T-O
2:1 = T-O-T
2:1:1 = “T-O-T O T-O-T”

38
Q

example of 1:1 layered sheet silicates

A

kaolinite (di-), serpentine(tri-)

39
Q

example of 2:1 layered sheet silicate

A

chlorite group minerals

40
Q

what goes between repeating 2:1 layered silicates

A

cations (K+) or cations and H2O

41
Q

key phyllosilicates (clay minerals)

A

kaolinite
muscovite
serpentine

42
Q

how are clays produced

A

weathering of anhydrous aluminosilicates

43
Q

what reaction forms serpentine and what does it do

A

Forsterite + water -> serpentine + brucite
serpentine lowers melting point of mantle at subduction zones

44
Q

What are framework silicates

A

continuous network of conjoined Si tetrahedra, with all 4 O bonded to a neighbouring tetrahedra

45
Q

phase transitions when heating quartz

A

low quartz -> high quartz -> tridymite -> cristobalite

46
Q

high pressure polymorph of quartz

A

coesite

47
Q

very high pressure polymorph of quartz created by impacts

A

stishovite

48
Q

physical structure of low quartz (alpha)

A

trigonal, 3 fold symmetry

FoG (7 decks)

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