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Flashcards in igneous rocks Deck (24):
1

igneous rock forming minerals

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

1

What determines felsic rock

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

2

What determines intermediate rock

22-25% mafic (dark) mineral

3

What determines mafic rock

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

4

What determines ultra mafic rock

Greater than 85% mafic (dark) minerals

5

Intrusive

Cooled slowly at depth or near surface
Large visible crystals
Plutonic

6

Extrusive

Cooled rapidly on surface
Volcanic
Too big to grow crystals

7

Extrusive rocks

Rhyolite
Andesite
Basalt
Obsidian basalt
Scoria
Pumice

8

Intrusive rocks

Granite
Diorite
Gabbros

9

Intrusive igneous features

Dike
Sill
Laccoliths
Batholiths

10

Dike

Tabular disconcordant pluton

11

Sill

Tabular concordant pluton

12

Laccoliths

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

13

Batholiths

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

14

Igneous textures

Phaneritic
Aphanitic
Porphyritic
Vitreous
Vesicular
Pegmatitic
Pyroclastic

15

Phaneritic

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

16

Aphanitic

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

17

Porphyritic

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

18

Vitreous

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

Vesicular

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

20

Pegmatitic

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

21

Pyroclastic

Contains volcanic fragments

22

What determines crystal size

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

23

Bowen's reactions series

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