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DISP Earth Science > Granite > Flashcards

Granite Flashcards

1
Q

What is a pluton?

A

a body of igneous rock crystallized from magma within the earth’s crust

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2
Q

What is the most common plutonic rock on continents?

A

granite

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3
Q

What minerals make up granite?

A

feldspar, quartz, mica

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4
Q

What types of feldspar are found in granite?

A

K-feldspar (>50%) and (Na,Ca)-feldspar (rest)

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5
Q

What is the most common accessory mineral in granite?

A

mica (biotite and muscovite)

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6
Q

How do biotite and muscovite mica differ in appearance?

A

biotite is black; muscovite is white

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7
Q

What mineral has the formula SiO2?

A

quartz

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8
Q

What is quartz’s hardness?

A

7

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9
Q

What type of fracture does quartz have?

A

conchoidal

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10
Q

What mineral is glassy?

A

quartz

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11
Q

How hard is feldspar?

A

6

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12
Q

What is a blocky mineral?

A

feldspar

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13
Q

What mineral makes up most of granite?

A

feldspar

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14
Q

What mineral in granite is quite soft?

A

mica

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15
Q

What is the structure of mica?

A

flexible sheets

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16
Q

What 5 characteristics of plutons led geologists to conclude that plutons were created from hot silicate liquids within the crust?

A
  • different texture than volcanic rocks of same mineralogy
  • surrounding rock broken and injected
  • surrounding rock metamorphosed (contact metamorphism)
  • grain size finer at margins of pluton (chilled margin)
  • inclusions of surrounding rock within pluton (xenoliths)
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17
Q

What rock has the same mineralogy as granite?

A

rhyolite

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18
Q

How do granite and rhyolite differ?

A

granite has much larger grains

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19
Q

Where is granite found?

A

with the crust beneath volcanoes

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20
Q

What is the coarse-grained equivalent to basalt?

A

gabbro

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21
Q

Which is more abundant between gabbro and basalt?

A

basalt

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22
Q

Which is more abundant between granite and rhyolite?

A

granite

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23
Q

Why does granite have larger crystals than rhyolite?

A

it took longer to cool (within earth’s crust), whereas rhyolite cooled quickly in a volcanic eruption

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24
Q

What sort of rocks does high silica magma make most often and why?

A

plutons - viscous, so barely ever makes it to surface for fast cooling

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25
Q

What type of rocks does low silica magma make most often and why?

A

volcanic rocks - not viscous, so flows out to make volcanoes easily

26
Q

How do the cracks of rocks get filled with granite?

A

hot silicate liquids rise through rock and create and fill fractures in surrounding rock, before freezing there

27
Q

What is metamorphism?

A

change in a rock’s minerals and/or texture by increasing temperature

28
Q

What often occurs at the boundary between bodies of rock?

A

contact metamorphism

29
Q

What does contact metamorphism indicate about a pluton?

A

that it must have been hotter than country rock

30
Q

What are chilled margins?

A

smaller crystals at the edges of a pluton

31
Q

What do chilled margins indicate?

A

quicker cooling - so the country rock must have been colder than magma

32
Q

What are xenoliths?

A

pieces of country rock that fell into magma pool and froze there

33
Q

How are xenoliths related to the country rock?

A

same rock

34
Q

What do xenoliths indicate about time frames?

A

the country rock must have been there before the pluton

35
Q

How does xenolith texture change depending on its distance from the contact point between the pluton and country rock?

A

angular near contact; rounded (and may have baked zone) further from contact

36
Q

How does cooling rate affect grain size?

A

big grains indicate slow (underground) cooling; little grains indicate fast (surface) cooling

37
Q

What are phenocrysts?

A

big crystals in rocks surrounded by little crystals

38
Q

How are phenocrysts formed?

A

cooled slowly underground at first, then magma erupted for fast cooling

39
Q

What is the difference between a sill and a dike?

A

sills are parallel to the host rock’s beds (concordant); dikes cross host rock (discordant)

40
Q

What are 2 shapes plutons can take?

A

sill and dyke

41
Q

What are the names for the different sizes of plutons (from smallest to largest)?

A

plut, stock, batholith

42
Q

How are deep plutons exposed?

A

through erosion

43
Q

What are some plutons associated with?

A

volcanic rocks

44
Q

What is a swarm?

A

many dykes in one area

45
Q

How big can batholiths get?

A

more than 1000 km long; about 100 km wide; 5-10 km thick

46
Q

What are batholiths made of?

A

many smaller plutons (each a few cubic km) with steep sides, flat roofs, and cross-cutting

47
Q

What is the geothermal gradient?

A

rate of increasing temperature with respect to increasing depth in Earth’s interior

48
Q

Where is partial melting predicted by the geothermal gradient?

A

depths of 70-250 km

49
Q

What does a 1-2% partial melt of peridotite yield?

A

basalt

50
Q

What is the asthenosphere?

A

the ductile part of the earth just below the lithosphere, including the upper mantle

51
Q

Why does magma rise?

A

due to density contrast

52
Q

What is stoping?

A

process by which magma intrudes - blocks of wall rock break off and sink into magma

53
Q

What is diapirism?

A

type of intrusion in which a more mobile and ductile material is forced into brittle overlying rocks and rises through buoyance; occurs lower in crust

54
Q

How does magma relate to the crust and mantle?

A

separates crust from mantle

55
Q

What does magma do to heat?

A

transfers heat from earth’s crust

56
Q

What moves lithospheric plates, builds continents, supplies hydrosphere/lithisophere, and modifies weather/climate?

A

magma

57
Q

What does magma transfer within reach of humankind?

A

matter and energy

58
Q

What is differential crystallization?

A

crystalization changes the composition of remaining magma (since some crystals solidify out of magma at higher temperatures)

59
Q

How does differential crystallization separate crystals from liquid?

A

crystals solidify at higher temperatures than other magma components and settle on the bottom

60
Q

What is partial melting?

A

magma produced from the first-melted portion of crust and mantle

61
Q

What does assimilation do to magma?

A

modifies composition and increases cooling

62
Q

What is assimilation?

A

when rocks fall in magma and partially melt/magma’s heat partially melts rock wall

DISP Earth Science (7 decks)

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