Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Atoms to volcanoes - 33739 > Felsic minerals and classification > Flashcards

Felsic minerals and classification Flashcards

1
Q

What are the most common continental felsic rocks?

A

granite
rhyolite

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the bulk geo-chemistry of felsic like compared to mafic?

A

Much more silica rich (70% for F, 50% for M)
Rich in alkalis
Poor Mg, Fe and Ca oxides

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What process is responsible for the difference in bulk Geo-chemistry of felsic and mafic?

A

Fractional crystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are alkalis that felsic can be rich in?

A

Na2O- sodium oxide
K2O- potassium oxide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How can the composition of felsic magma also be referred to as?

A

Evolved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does it mean to say felsic magma is evolved?

A

magma experienced modification from primitive mafic mainly via fractional crystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is fractional crystallisation?

A

early formed crystals removed- thus the minerals that form them are used creating a dilution affect of liquid melt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the first minerals to form in a cooling basalt?

A

olivine
pyroxene
Ca-rich plagioclase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What will the the same and what will be variable in the evolved rocks?

A

Not all same silica content
Rich be rich in felsic minerals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What elements typically make up felsic minerals?

A

Al, Si, K, Na

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are some examples of minerals rich in felsic minerals ?

A

Feldspars (alkali feldspars)
Quartz or feldspathoids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the general reason rocks will become evolved?

A

as the magma crystallises the minerals forming have a chemistry that doesn’t match liquid melt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the first minerals to form from cooling basalt usually composed of?

A

rich in- Mg Fe Ca
Poor in silica

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are compatible elements?

A

elements that go into a specific mineral

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are incompatible elements?

A

those which dont go into phases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What will happen to the liquid melt during crystallisation involving incompatible?

A

liquid melt will become enriched in incompatible elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What can fractional crystallisation produce graphically?

A

a continuous spectrum of real magma compositions from mafic starting to felsic end

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are the common minerals in felsic igneous?

A

Quartz
Feldspars
Micas- muscovite and biotite
Hornblende
Magnetite (opaque oxide phases)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the equation for quartz?

A

SiO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Where is quartz commonly found?

A

widespread in upper continental crust

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is quartz common in?

A

felsic igneous rocks
metamorphic rock
clastic sediments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What will the framework of quartz be like?

A

SiO2 tetrahedra

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How many polymorphs of silica are there?

A

6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is the stability of the silica polymorphs like?

A

all stable at different pressure and temperature

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What is the stability of quartz like?
stable at low temp and pressure (upper continental crust) highly resistant to weathering Very hard
26
What will quartz appear like in igneous hand specimen?
grey glassy looking mineral no cleavage instead glassy conchoidal fractures
27
What is quartz like in thin section?
colourless low relief low birefringence no twinning no cleavage Clean even when around altered minerals Undulose extinction
28
What is undulose extinction and why does it occur in quartz?
occurs when structure is strained it is extinction sweeping across grain as platform is rotated
29
What elements will you typically find in feldspars?
(Ca, Na, K) Al (Al, Si) Si2O8
30
Where are feldspars dominant?
the crust- continental and oceanic
31
What is the framework of feldspars like?
alumino-silicates Si and Al in tetrahedral framework
32
What 2 series exist for feldspar in solid solution?
Plagioclase feldspars Alkali feldspars
33
What ion exchange occurs in plagioclase feldspars?
Na-Si Ca-Al
34
What do you transfer to and from with plagioclase feldspar?
Albite (Na) to Anorthite (Ca)
35
What endmembers is there no natural transfer between? (feldspars)
Potassium and Calcium (orthoclase and Anorthite)
36
What can alkali feldspars transition inbetween?
Orthoclase Albite
37
What ion exchange takes place with alkali feldspars?
Na and K (sodium and potassium)
38
What are the common elements found in plagioclase feldspar?
(Ca, Na) Al (Al, Si) Si2O8
39
What can the more complex exchange in solid solution of plagioclase feldspar lead to?
reaction to changing magmatic conditions can be slow and lead to compositional zoning
40
What is zoning in crystallisation?
bands of light and dark crystal contained inside crystal border almost radiating from a central nucleus
41
How will plagioclase feldspar appear in hand specimen?
white blocky grains
42
What will plagioclase feldspar be like in thin section?
low relief colourless low birefringence Unclear cleavage - can show 2 (90*- cubic) Polysynthetic twinning (multiple or lamellar) Altered (dusty)
43
What is K feldspar?
K-rich alkali feldspar
44
What will K feldspar in hand specimen?
pinkish colour can also be white
45
What will K feldspar be like in thin section?
Similar to plagioclase but instead simple twinning
46
What will twinning be like in a low T-form microcline?
might be cross-hatched
47
What can the texture of coarsely-crystalline alkali feldspars be called?
perthite- "flame", "patchy" and "lamellar"
48
What are the 2 common mica minerals in igneous rocks?
Biotite Muscovite
49
What are the important bits to remember from biotite formula?
Hydrous- OH- anion Range of cations- Al, K, Fe, Mg
50
What is biotite more commonly referred to as?
Dark mica
51
What is the general thing to take away from muscovite formula?
Al rich (different from biotite as absence of Fe and Mg)
52
What is muscovite more commonly referred to as?
white mica
53
What type of silicates are micas?
sheet silicates
54
What is the structure of micas like?
tetrahedra link in sheet form (perfect cleavage between sheets) Thin platy grains break with basal cleavage Grain shape hexagonal in other plane
55
How can micas be recognised in hand specimen?
strong cleavage reflective surface- biotite: black, muscovite: silvery
56
What will biotite be like in thin section for ppl?
Pleochroic brown Moderate relief One very good cleavage Alteration prone
57
What can happen to the cleavage in thin section for biotite?
kinked due to mineral weakness causing irregular crystal ends
58
What will alteration look like in biotite thin section?
patchy
59
What is biotite like in xpl thin section?
high birefringence (third order) Extinction grains have speckled texture
60
What is muscovite like in thin section ppl?
Colourless One very good cleavage
61
What can the kinking of the cleavage in muscovite lead to?
irregular crystal and development of woody texture
62
What is muscovite like in thin section xpl?
high birefringence (upto 3rd order)
63
What does crystal size relate to in igneous rocks?
cooling rate
64
What is the factor that distinguishes basalts from gabbro due to chemical and mineralogical sameness?
texture- crystal size
65
What will a slow cooling rate do to crystallisation?
coarser crystals
66
Where will extrusive rocks form?
on the surface
67
What does the surface cooling environment mean for extrusive rocks?
heat lost rapidly liquid magma will crystallise quickly finer grained
68
Where do intrusive rocks cool and solidify?
in the crust
69
What are some examples of shallow intrusions?
Sills Dykes
70
What can shallow intrusions also be called?
hypabyssal rocks
71
What is cooling rate like with hypabyssal rocks?
small size lose heat relatively quickly
72
What is the typical grain size of hypabyssal rocks?
medium to fine grained
73
What 2 broad types of intrusive body?
hypabyssal plutonic
74
What are plutonic intrusive bodies?
larger greater depth (few km)
75
What is cooing rate and crystal size like in plutonic bodies?
generally slower forming coarser crystals
76
What will the hand specimen of plutonic rocks be like?
granular texture - formed due to large interlocking crystals
77
How will crystal formation and nucleation be affected by rapid cooling?
many crystals nucleate but dont have time to grow into larger crystals
78
What is nucleation for crystallisation?
initial process of crystal formation from solution

Atoms to volcanoes - 33739 (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions