igneous rates of cooling Flashcards

1
Q

the slower the rate of cooling….

A

.. the larger the crystal size

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2
Q

crystal size in glassy ign rocks

A

no crystals

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3
Q

crystal size in fine grain ign rocks

A

> 1mm

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4
Q

medium grained ign rock

A

1-5mm

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5
Q

coarse grained ign rock

A

> 5mm

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6
Q

rate of cooling igneous rock: glassy

A

very quickly, within hours, usually in sea as water cools magma fast

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7
Q

rate of cooling igneous rock: fine

A

rapid cooling over weeks or months

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8
Q

rate of cooling igneous rock: medium

A

fairly slow cooling- few thousand years

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9
Q

rate of cooling igneous rock: coarse

A

cools very slowly over millions of years

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10
Q

where do ign glassy rocks form?

A

at surface, ALWAYS volcanic extrusive

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11
Q

where do ign fine rocks form?

A
  1. at surface in EXTRUSIVE volcanic rocks as lava flows

2. in chilled margins at the edges of minor intrusions

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12
Q

where to ign medium rocks form:?

A

below the surface in minor intrusions ~1km down (hypabysall)

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13
Q

where do ign coarse rocks form?

A

in major inrustions at great depth >10km, as batholoiths or plutonic rocks.

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14
Q

define EXTRUSIVE

A

general term for all igneous rocks that cool at the surface (both lava and pyroclasts)

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15
Q

define INTRUSIVE

A

term for igneous rocks that cool below the surface

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16
Q

define HYPABYSALL

A

when igneous rocks form at relativley shallow depths below the surface

17
Q

define PUTONIC

A

when igneous rocks form deep below the surface

18
Q

why glassy textures form

A

lava flows into the sea and cools very rapidly, so no time for crystals to form (IE. obsidian)

19
Q

what is a pegmatite?

A

an igenous rock with very large crystals can beseveral cms or even metres

20
Q

how do pegmaities form?

A

in the last stages of crystallisation, from water rich residual magma