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CIVIL two twenty > igneous rock > Flashcards

igneous rock Flashcards

1
Q

petrology

A

study of rocks

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2
Q

lava vs magma

A

lava is magma that has erupted

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3
Q

igneous rocks form from….

A

cooling of magma

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4
Q

3 ways of magma formation

A
  • decompression melting (pressure drop)
  • flux melting (add volatiles H2O CO2 SO2)
  • heat transfer from rising magma
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5
Q

_______ magma is the most abundant magma, it is of ________ composition and generated in the ______

A

mafic magma is the most abundant magma, it is of basaltic composition and generated in the mantle

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6
Q

_________ and ______ magmas are of ________ to rhyolitic composition, and are generated in the _____

A

intermediate and silicic magmas are of andesitic to rhyolitic composition, and are generated in the crust

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7
Q

how does addition of volatiles help melt mantle rock? what type of magma is formed

A
  • break molecular bonds
  • decreases melt temp
  • basaltic magma (mafic) formed
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8
Q

magma is _______ (silicic) if melted crust alone rises in Heat transfer

A

magma is rhyolitic (silicic) if melted crust alone rises in Heat transfer

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9
Q

formation of andesitic (intermediate) magma in heat transfer

A

basaltic magma and melted crust mix

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10
Q

BOWEN’s Reaction series

A

dictates what minerals crystalise at what temperatures

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11
Q

according to BOWEN’s reaction series, what crystallises at high T and Low T

A

high T- Mafic minerals

low T- Felsic minerals

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12
Q

three igneous rock textures

A
  1. Aphanitic - fine
  2. Phaneritic - coarse
  3. Porphyritic - large phenocrysts in fine matrix
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13
Q

eg of aphanitic

A

basalt

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14
Q

eg of phaneritic

A

gabbro

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15
Q

eg of porphyritic

A

andesite

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16
Q

magma thats cooled over centuries would form

A

phaneritic texture

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17
Q

main way to classify igneous rock, based on chemical composition

A

silica content (SiO2)

18
Q

most silica = ,

least silica = , and ,

A

most silica = silicic,

least silica = mafic, ultramafic and ,

19
Q

3 environments igneous rock forms in

A
  1. Plutonic environment - High P, slow cooling
  2. subvolcanic/ hypabyssal - transitional
  3. volcanic
    - low P, fast cooling
20
Q

most common plutonic rock in the continental crust

A

granite

21
Q

gabbro (mafic) forms significant part of what?

A

oceanic crust

22
Q

how are plutonic rocks found on the surface of the earth?

A

by uplift and erosion

23
Q

peridotite is what type of mineral?

A

ultramafic

24
Q

example of intermediate, phaneritic rock

A

Diorite

25
Q

dyke

A

cross-cutting, flat sheet cuts across rock layers

26
Q

sill

A

parallel to local structures

27
Q

effusive volcanic activity

A
  • forms crystalline rock
  • magma extruded at the ground surface
  • little gas involved
28
Q

explosive volcanic activity

A

forms clastic rock

29
Q

2 variances of rhyolite

A

Pumice and obsidian

30
Q

basalt forms from ___ viscosity lava. Andesite forms from ___ viscosity lava. Dacite forms from ____ viscosity lava.

A

low, medium, medium-high

31
Q

IGNIMBRITE

A

pumice-dominated (glassy) pyroclastic flow deposits

32
Q

2 major groups of igneous rocks

A
  1. volcanic - extruded onto the earths surface

2. plutonic - cooled from magma inside the crust

33
Q

having same chemical composition what are the plutonic equivalents of:
Basalt =
Andesite & Dacite =
Rhyolite =

A

Basalt = Gabbro
Andesite & Dacite = Diorite
Rhyolite = Granite

34
Q

Basalt colour and varieties

A

dark grey. Vesicular variety and Scoria variety

35
Q

some uses of Basalt include…

A

aggregate, fill in construction, armour rock, scoria for drainage

36
Q

colour of andesite vs basalt

A

lighter grey

37
Q

Andesite uses

A

aggregate fill in roading and construction (not good in concrete due to high silica)

38
Q

Rhyolite is light-coloured, name 3 varieties:

A
  1. Obsidian (glassy)
  2. pumice (vesicular)
  3. Ignimbrite (lithification of ash and pyroclastic flow)
39
Q

Gabbro colour and uses

A

very dark black. Used as aggregate and as a building stone in foyers etc. (‘black granite’)

40
Q

what will happen if an aggregate with high silica content or glass is used in cement?

A

reacts with cement to produce swelling materials which will result in cracking

41
Q

what mineral would be good in an aggregate for cement?

A

ferromagnesium

42
Q

would granite bind well with bitumen? why/why not?

A

NO, it has large mineral grains

CIVIL two twenty (16 decks)

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