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Flashcards in igneous rocks Deck (24)
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1
Q

igneous rock forming minerals

A

felsic- quartz, plagioclase & potassium feldspar, muscovite mica
mafic- biotite mica, amphibole, pyroxene, olivine

1
Q

What determines felsic rock

A

Less than 25% mafic minerals
Feldspar and silica (quartz)
Almost entirely of light colored silicates with small amts of micas or hornblende

2
Q

What determines intermediate rock

A

22-25% mafic (dark) mineral

3
Q

What determines mafic rock

A

55-85% mafic minerals
Basaltic
Magnesium and ferrum
Contains substantial dark silicate minerals and calcium rich plagioclase feldspar

4
Q

What determines ultra mafic rock

A

Greater than 85% mafic (dark) minerals

5
Q

Intrusive

A

Cooled slowly at depth or near surface
Large visible crystals
Plutonic

6
Q

Extrusive

A

Cooled rapidly on surface
Volcanic
Too big to grow crystals

7
Q

Extrusive rocks

A
Rhyolite
Andesite
Basalt
Obsidian basalt
Scoria
Pumice
8
Q

Intrusive rocks

A

Granite
Diorite
Gabbros

9
Q

Intrusive igneous features

A

Dike
Sill
Laccoliths
Batholiths

10
Q

Dike

A

Tabular disconcordant pluton

11
Q

Sill

A

Tabular concordant pluton

12
Q

Laccoliths

A

Similar to a sill
Lens or mushroom shaped mass
Arches overlying strata upward

13
Q

Batholiths

A

Largest intrusive body
Surface exposure >100 sq km
Smaller bodies termed stocks
Frequently form the cores of mts

14
Q

Igneous textures

A
Phaneritic
Aphanitic
Porphyritic
Vitreous
Vesicular
Pegmatitic
Pyroclastic
15
Q

Phaneritic

A

Coarse grained
Crystals greater than 1mm but less thn 1 cm
Slow cooling intrusive
Crystals have time to grow

16
Q

Aphanitic

A

Fine grained
Crystals less than 1 mm
Fast cooling extrusive
Crystals don’t have time to grow

17
Q

Porphyritic

A

Two distinct crystal sizes
Larger/independent crystals called phenocrysts-slow cooling
Mix of coarse and fine crystals
Indicate a 2 stage history

18
Q

Vitreous

A
Compact or frothy glassy 
Rapid cooling of  lava in water or air 
Obsidian-lava flowing in water 
Pumice- frothy felsic full of vesicles 
Scoria- glassy vesicular mafic
19
Q

Vesicular

A

Holes formed from gas-charged lava
Rapid rate of cooling
Gas bubbles

20
Q

Pegmatitic

A

Crystal size greater than 1 cm
Exceptionally coarse
Made from ions that don’t easily fit into crystals
Some rich in prized minerals

21
Q

Pyroclastic

A

Contains volcanic fragments

22
Q

What determines crystal size

A

Rate of cooling magma
Slow cooling- large crystals
Fast cooling- microscopic crystals
Very fast cooling- glassy

23
Q

Bowen’s reactions series

A

Magma crystallize over a temp range of several 100 degrees
Minerals crystallize in predictable order
Last minerals to crystallize are very diff in composition from the earlier formed minerals