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Flashcards in IGNEOUS Deck (38)
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1

Silicic rocks are rich in which minerals?

Feldspar and silica (quartz)
Mica (biotite muscovite)
F'spa (potassium plagioclaise)

2

Mafic rocks are rich in which minerals?

magnesium and iron (ferric)
Plagioclaaise f'spa
augite
Olivene

3

fine grained silicic

Pumice Rhyolite

4

fine grained intermediate

Andersite

5

Fine mafic

Bassalt

6

medium mafic

dolerite

7

coarse silicic

Granite

8

intermediate coarse

Diorite

9

Mafic Coarse

Gabbro

10

ultramafic coarse

Peridotite

11

what are the essential minerals?

are the main ones; so mafic rocks largely
consist of plagioclase and a pyroxene such as
augite
.

12

what are accessory minerals?

Occur in smaller quantities

13

quarts:
Composition:
Hardness:
Density:
Colour:
streak:
Cleavage:
Luster:


SiO2
7
2.7
usually white or colourless
White
none
Vistreous

14

Orthoclase feldspar:
Hardness:
Density:
Colour:
streak:
Cleavage:
Luster:


6–6.5
2.6
white or pink short flat crystals
white
2 good. Has the stair-step cleavage characteristic of feldspars.
vistreous

15

Plagioclase f'spar
Hardness:
Density:
Colour:
streak:
Cleavage:
Luster:



6–6.5
average
white or gray
white
2 good
vistreous

16

Olivene:
Hardness:
Density:
Colour:
streak:
Cleavage:
Luster:

never occurs with quarts
6.5–7
high
olive green
colourless
poor
vistreous sugary

17

Pyroxene: Augite
Hardness:
Density:
Colour:
streak:
Cleavage:
Luster:


5–6
above average
greenish black
vitreous
2 poor
vistreous

18

AMPHIBOLE:HORNBLENDE
Hardness:
Colour:
Cleavage:
Crystals:


5–6
black, dark green
2 perfact at 60/ 120
needle like crystals

19

Wich rock is amphible common in?

intermediate
rocks such as diorite, less so in granite or
gabbro

20

In which rocks is muscovite mica most aboundant?

Silicic

21

in which rocks is biotite mica most abundant?

Intermediate

22

what makes rocks eqigranular?

Steady cooling

23

what makes rocks glassy?

Instantaneous cooling

24

what is pophoritic texture and how is it caused?

Mixture of grain sizes caused by mixed cooling history; slow
cooling first, followed by a period of somewhat faster
cooling.

25

define:
Phenocrysts:
Groundmass:


large crystals
finer surrounding crystals

26

what is flow banding?

A streaky texture more or less parallel to bedding.
Diagnostic of lavas.

27

Oceanic crust:
composition?
Thickness?
fate?

-Igneous with thin
sediments. Basalts and gabbros=mafic composition No metamorphics
-7-10 km
-Subduction

28

Continental crust:
composition?
Thickness?
fate?

-varied with thick sediments and metamorphics Overall silicic with many granites.
-35 to 40 km
-grows by accretion

29

what is the structure of an ophiolite?

ultramafic rocks at the base, layered gabbros, basaltic dykes
then pillow lavas and then in places,
thin deep water sediments.

30

What are ophiolites?

slices of oceanic crust that have been
trapped and pushed up instead of
being subducted.