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Eduqas GCSE Geology (9-1) > 1.2 Igneous Rocks and Processes > Flashcards

1.2 Igneous Rocks and Processes Flashcards

1
Q

How is magma formed?

A

When the heat in the earth melts rocks to form molten material

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2
Q

What does magma contain?

A

Molten rock, as well as volatiles such as gas and water

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3
Q

Where might magma be found?

A
  • lower continental crust
  • lower oceanic crust
  • top of the mantle
  • core/mantle boundary
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4
Q

What are some examples of igneous rocks?

A
  • peridotite
  • granite
  • dolerite
  • basalt
  • obsidian
  • andesite
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5
Q

Description of olivine in an igneous rock?

A

Green and glassy

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6
Q

Description of plagioclase fledspar in an igneous rock?

A

White

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7
Q

Description of orthoclase feldspar in an igneous rock?

A

Fleshy-pink

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8
Q

Description of quartz in an igneous rock?

A

Grey and glassy

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9
Q

Description of biotite mica in an igneous rock?

A

Black and flaky

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10
Q

Description of muscovite mica in an igneous rock?

A

White and flaky

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11
Q

Description of ferromagnesian minerals in an igneous rock?

A

Black

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12
Q

What are the four types of magma from which igneous rocks crystallise?

A
  • silicic magma
  • intermediate magma
  • mafic magma
  • ultramafic magma
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13
Q

What experiment can be used to show how the rate of cooling with affect crystal size/texture of the igneous rock?

A
  • substance called SALOL - melts and crystallises at lower temperatures than magma
  • drops put onto warm piece of glass and also a cold
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14
Q

What are the four main rates of cooling of magma to form igneous rocks?

A
  • slow
  • moderate
  • rapid
  • very rapid
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15
Q

What factors vary the type of igneous rock formed?

A
  • type of magma

* rate of cooling

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16
Q

What does it mean in an igneous rock, if the crystals are aligned?

A

Indicates direction of flow of magma

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17
Q

What is porphyritic texture?

A

Larger crystals (phenocrysts) embedded in a fine-grained groundmass

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18
Q

What are the large crystals in a porphyritic texture called?

A

Phenocrysts

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19
Q

At what rate did the phenocrysts in porphyritic textured igneous rock cool?

A

Slowly, deep in the crust

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20
Q

What are the smaller, poorly formed crystals in porphyritic textured igneous rock called?

A

Groundmass

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21
Q

At what rate did the grounmass in porphyritic textured igneous rock cool?

A

A moderate/rapid rate, near to earth’s surface

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22
Q

In granite, which mineral are the phenocrysts formed from?

A

Feldspar

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23
Q

In granite, which minerals form the groundmass?

A

Quartz and mica

24
Q

What type of magma did granite cool from?

A

Silicic

25
Q

What is the crystal size in igneous rocks related to?

A

The cooling rate of the magma

26
Q

How can igneous rocks be classified?

A
  • texture

* mineralogy

27
Q

How would a crystal size >3 mm be classified?

A

Coarse

28
Q

How would a crystal size <1 mm be classified?

A

Fine

29
Q

When magma cools in the crust, what type of igneous rocks are formed?

A

Intrusive

30
Q

When magma cools on the surface of the crust, what type of igneous rocks are formed?

A

Extrusive or volcanic

31
Q

What is a xenolith?

A

A piece of the country rock that has fallen into the magma but not completely melted

32
Q

How are dykes formed?

A

When molten magma flows upward through vertical faults toward the surface and cools

33
Q

What is a batholith?

A

A giant mass of intrusive igneous rock that forms when magma collects and cools deep in the earth’s crust without being exposed to the surface

34
Q

How is a laccolith formed?

A

When magma pushes through layers of rock above it and pools in a dome shape

35
Q

What is a sill?

A

A flat intrusion of igneous rock that forms between preexisting layers of rock

36
Q

Given that magma is hot, what do igneous intrusions do to country rock?

A

Bakes/burns it

37
Q

Why can sills and lava flows sometimes be confused?

A

They are both layers of igneous rock that follow the bedding

38
Q

How might you identify between sills and lava flows?

A
  • veins on upper surface of sills
  • sills have rock with medium crystals, lava flows have rock with fine
  • lava flow - baking only on lower surface
39
Q

What does magma viscosity affect?

A

The type of volcanic activity and shape of volcanoes

40
Q

Characteristics of granitic magma?

A

Sticky and viscous

41
Q

Characteristics of andesitic magma?

A

Quite viscous, but can flow more easily than granitic

42
Q

Characteristics of basaltic magma?

A

Can flow easily → fluid

43
Q

Order of viscosity of magmas?

A

Basaltic < Andesitic < Granitic

44
Q

What is the shape of basaltic volcanoes?

A

Shield volcanoes - gradual sides, convex

45
Q

Type of activity in basaltic volcanoes?

A

Fissure eruption and central cone

46
Q

Main products from basaltic volcanoes?

A

Basaltic lava

47
Q

Examples of locations for basaltic volcanoes?

A

Hawaii and Iceland

48
Q

What type of volcano might Ropy or Pahoehoe lava flows be formed from?

A

Basaltic volcanoes

49
Q

What is a Pahoehoe lava flow?

A

Wrinkled lava surface resembling ropes - where surface cooled quicker than underlying lava flow - so hasn’t been able to move smoothly

50
Q

What type of volcano might columnar jointing be formed from?

A

Basaltic volcanoes

51
Q

What is columnar jointing?

A

Joints formed perpendicular to cooling surface - columns form as a result

52
Q

How does columnar jointing occur?

A

When lava cools and contracts

53
Q

What type of volcano might pillow lavas be formed from?

A

Basaltic volcanoes

54
Q

What are pillow lavas?

A

When basalt lava is erupted underwater and gases can’t escape easily - lava squeezed out from front of lava flow and rounded by sea water

55
Q

What type of volcanoes are andesitic volcanoes?

A

Composite cone volcanos

56
Q

What type of volcano produces volcanic bombs (pyroclasts)?

A

Andesitic volcanoes

57
Q

What is equicrystalline texture?

A

Even cooling, all crystals 1.0 – 1.5 mm

Eduqas GCSE Geology (9-1) (13 decks)

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