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Geology > Igneous Rocks > Flashcards

Igneous Rocks Flashcards

1
Q

Silicic minerals

A

Quartz
Orthoclase
Plagioclase
Muscovite

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2
Q

Mafic minerals

A

Biotite
Hornblende
Augite
Olivine

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3
Q

What is Acid/silicic magma?

A

> 66% SiO
C-O
most explosive

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4
Q

What is Intermediate magma?

A

55-65% SiO

O-O

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5
Q

What is Basic/Mafic magma?

A

45-55% SO

Mid-plate got spits and oceanic ridges

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6
Q

What is Ultrabasic/Ultramafic magma?

A

<44% SiO
Asthenosphere
Least explosive

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7
Q

Grain size

A

Coarse- >5.0mm
Medium- 0.1-5.0mm
Fine- <0.1mm

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8
Q

Example of a silicic rock?

A

Granite

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9
Q

Examples of mafic/basic rocks?

A

Gabbro
Dolerite
Basalt

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10
Q

Example of an Ultra mafic/ Ultrabasic rock?

A

Peridotite

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11
Q

What is holocrystalline?

A

Rocks that are wholly crystalline I.e entirely composed of silicate crystals

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12
Q

What is glassy?

A

Rocks that are composed of natural glass such as obsidian. This texture develops when lava cools very quickly and is unable to form crystals

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13
Q

What is porphyritic?

A

The rock contains large crystals called phenocrysts set in a matrix of finer crystals.

Phenocrysts form first at higher temperatures where they were unrestricted.

The matrix formed lager when magma had cooled at a lower temperature

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14
Q

What is euhedral?

A

Crystals that show well developed crystal faces. They crystallise first at higher temperatures and were unrestricted. Usually phenocrysts.

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15
Q

What is anhedral?

A

Crystals that show poorly developed crystal faces. They formed at the late stage at lower temperatures so their development was restricted

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16
Q

What is groundmass?

A

Mosaic of small crystals that form in the spaces left behind by earlier formed crystals

17
Q

What is granular?

A

Rocks composed of similar sized silicate crystals. This texture is formed when all the crystals begin to form at the same temperature and grew at the same rate

18
Q

What is vesicular?

A

Holes seen in lava rocks that are created by escaping gas bubbles

19
Q

What is fragmental tuff?

A

Volcanic rocks composed of angular rock, mineral and ash that has been blasted out of a volcano following an eruption

20
Q

Granite

A 
Crystalline
Coarse
Plagioclase Feldspar showing cleavage 
Anhedral Biotite 
Euhedral crystals of Orthoclase Feldspar 
Quartz
21
Q

Gabbro

A 
Coarse grained
>5mm
Very slow cooling 
Basic magma 
Magma chamber
22
Q

Dolerite

A 
Medium grained
0.1- 5mm 
Moderately slow grained 
Basic magma 
Small and shallow intrusions 
Dyke or sill
23
Q

Basalt

A

Fine grained
<0.1mm
Rapid cooling
Surface lava

24
Q

Pillow lava

A 
Ball shaped masses
Eruption of lava in water 
1m in size 
Kidney bean shaped 
Upper convex surface 
Lower concave surface
25
Q

Columnar jointing

A

Six sided columns of igneous rocks created by contracting magma or lava during cooling

26
Q

Amygdales

A

Secondary minerals that infill vesicles

27
Q

Pahoehoe

A

Ropey structure seen on the surface of lava flow caused by compression of surface lava in ridges as it is slowing more slowly that the lava below

28
Q

Aa

A

A block structure seen on the surface of lava. Formed by the rapid loss of gas from the lava as it erupts

29
Q

Dyke

A

Sheet of igneous rock that is formed when magma is injected into a crack

It is discordant
Few cms to a few kms 
Creates baked margins 
Medium grained 
Fine grained chilled margins
30
Q

Will

A

Magma is injected along a bedding plane

Concordant

Geology (14 decks)

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