FoG1 - Mineralogy

Question 1

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

Answer 1

orthosilicate (isolated tetrahedra)

Question 2

example of orthosilicate

Answer 2

olivine, garnet, zircon

Question 3

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

Answer 3

chain silicate

Question 4

example of chain silicate

Answer 4

pyroxene

Question 5

how do chain silicates charge balance

Answer 5

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

Question 6

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

Answer 6

double chain silicate

Question 7

example of double chain silicate

Answer 7

amphibole

Question 8

Why can double chain silicates fit large cations in its structure

Answer 8

irregular octahedra leave large holes in structure

Question 9

how do double chain silicates charge balance

Answer 9

layer of octahedra between 2 double chain silicate layers

Question 10

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

Answer 10

sheet silicate

Question 11

how do sheet silicates charge balance

Answer 11

have 2+ or 1+ cations in gaps in structure

Question 12

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

Answer 12

3d framework

Question 13

example of 3d framework silicate

Answer 13

quartz

Question 14

example of sheet silicate

Answer 14

mica (biotite)

Question 15

what is the structure of feldspars

Answer 15

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

Question 16

what structure has 3 cations

Answer 16

triangular

Question 17

what structure has 4 cations

Answer 17

tetrahedra

Question 18

what structure has 6 cations

Answer 18

octahedral

Question 19

what structure has 8 cations

Answer 19

cubic

Question 20

what structure has 12 cations

Answer 20

cuboctohedral

Question 21

end members of olivine

Answer 21

forsterite = Mg
fayalite = Fe

Question 22

types of garnet

Answer 22

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

Question 23

name 3 polymorphs pf aluminosilicate (Al2 SiO5)

Answer 23

kyanite
andalusite
sillimanite

Question 24

P-T of andalusite

Answer 24

low temp

Question 25

P-T of sillimanite

Answer 25

high temp high pressure

Question 26

P-T of kyanite

Answer 26

high pressure

Question 27

why are zircons so good for dating

Answer 27

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

Question 28

solid solution for pyroxenes

Answer 28

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

Question 29

solid solution for pyroxenes with 50% Calcium

Answer 29

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

Question 30

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

Answer 30

Pigeonite = some Ca Augite = less than 50% Ca

Question 31

name of pyroxenes with <5% Ca

Answer 31

Orthopyroxene

Question 32

name of pyroxene with 5-50% Ca

Answer 32

Clinopyroxene

Question 33

general amphibole

Answer 33

Hornblende

Question 34

physical characteristics of phyllosilicates

Answer 34

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

Question 35

what do most phyllosilicates have at centre of hexagons

Answer 35

-OH group (water)

Question 36

2 ways of arranging octahedra in a sheet

Answer 36

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

Question 37

types of layering sheet silicates

Answer 37

1:1 = T-O 2:1 = T-O-T 2:1:1 = "T-O-T O T-O-T"

Question 38

example of 1:1 layered sheet silicates

Answer 38

kaolinite (di-), serpentine(tri-)

Question 39

example of 2:1 layered sheet silicate

Answer 39

chlorite group minerals

Question 40

what goes between repeating 2:1 layered silicates

Answer 40

cations (K+) or cations and H2O

Question 41

key phyllosilicates (clay minerals)

Answer 41

kaolinite muscovite serpentine

Question 42

how are clays produced

Answer 42

weathering of anhydrous aluminosilicates

Question 43

what reaction forms serpentine and what does it do

Answer 43

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

Question 44

What are framework silicates

Answer 44

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

Question 45

phase transitions when heating quartz

Answer 45

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

Question 46

high pressure polymorph of quartz

Answer 46

coesite

Question 47

very high pressure polymorph of quartz created by impacts

Answer 47

stishovite

Question 48

physical structure of low quartz (alpha)

Answer 48

trigonal, 3 fold symmetry