Bowens Reaction Series

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Bowens Reaction Series
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Introduction to Igneous Minerals and Rocks Thin
Section Analysis of Samples
The Virtual Microscope
http//www.gly.bris.ac.uk/WWW/TerraNova/ouvm/OUVM.
html
Petrography
http//sorrel.humboldt.edu/jdl1/petrography.page.
html
http//www.geo.wvu.edu/lang/Geol284/Min7Optical/
Check out these granites!!!
http//www.marbleandgranite.com/frame_granite.html
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Relief Birefringence Pleochroism Cleavage Fractur
ing Twinning Zoning
Phaneritic Aphanitic
Intrusive (Plutonic) Extrusive (Volcanic)
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Olivine
Generally found in Gabbro (intrusive rock)
Basalt (extrusive rock)
High Relief High Birefringence Fracturing
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An intrusive, mafic rock composed of more than
90 Olivine is called a Dunite.
Mineralogy A dunite has gt90 Olivine
Mineral Diagnostics Fracturing of crystals
Very bright colors High Relief under plain
polarized light
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Pyroxene
Generally found in Mafic and intermediate
rocks (Gabbros/basalts to andesites)
Medium Relief High Birefringence 90o-90o Cleavage
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XPL
PPL
Biotite
PPL
XPL
Amphibole
Amphibole
Medium Relief Med-high Birefringence 120o-60o
Cleavage Brown/green in plain polarized light
Generally found in Intermediate to Felsic
rocks Diorites/andesites/dacites to Granites.
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PPL
XPL
PPL
Biotite
What are these?
Generally found in Intermediate to Felsic
rocks (Diorite/dacite to granite)
Brown to green under plain polarized light (PPL)
Dominant cleavage plain Bladed to wispy
shape Birds eye or Tree bark extinction
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Polysynthetic Twinning in Plagioclase Feldspar
Generally found in Mafic to Felsic rocks
(Gabbro/basalt to Granite)
Low relief Colorless in PPL Best identified by
twinning and low-order (greys) colors
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Tartan and Carlsbad Twinning in Alkali Feldspar
Generally found in Felsic rocks (Granites)
Low relief Colorless in PPL Best identified by
twinning and low-order (greys) colors
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Alkali Feldspar does not have to have
Tartan and Carlsbad Twinning
Feldspars also often show zoning. The zones shown
in this plagioclase feldspar indicate that the
chemistry of the magma was changing as the
crystal grew.
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PPL
Muscovite
Biotite
Muscovite
Generally found in Felsic rocks (Granites)
Med-Low relief Colorless to mild pleochroic in
PPL Bladed to wispy shape Birds eye or Tree
bark extinction --like biotite, but pinky-green
colors
XPL
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Quartz
Generally found in Felsic rocks (Granites)
Low relief Colorless in PPL Conchoidal
fracturing Undulatory extinction
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Intrusive Mafic Rock Gabbro
Minerals Olivine, Plagioclase
Minerals Pyroxene, Plagioclase
Gabbros have more than 35 ferromagnesian
minerals, and plagioclase composition in greater
than 50 Ca in crystal lattice site. Gabbro is
the intrusive equivalent of basalt.
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Basalt Volcanic (Extrusive) Mafic Rock
Pyroxenes and/or Olivines
Plagioclase Feldspars (High in Ca)
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Intrusive Intermediate Rock Diorite
Diorites contain less than 35 ferromagnesian mine
rals 30-50 Ca in plagioclase composition. Diorit
es are common in batholiths associated with
subduction zones. They are the intrusive
equivalents of andesites.
PPL
amphibole
XPL
amphibole
Plagioclase feldspars
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Andesites Intermediate extrusive (volcanic) rocks
Andesites consist of intermediate composition
plagioclase (typically, An30-50), and less than
35 of ferromagnesian minerals such as pyroxene,
hornblende, or olivine. Andesites are most
abundant in subduction-related arc
volcanoes. The photographs above (crossed
polarizers on left, plane polarized light on
right) show zoned and twinned plagioclase
crystals in a matrix of glass and plagioclase
microcrystals.
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Granites High-silica (felsic) intrusive rocks
Quartz
Feldspars
Amphibole
Biotite
Quartz
K Feldspar
Granites are abundant in continental shield areas
and in deeply eroded folded mountain belts. They
are the intrusive equivalent of rhyolites.
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Granites!!!!
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Extrusive (volcanic) Felsic Rock Rhyolite
K Feldspar (Sanidine)
flow banded matrix
PPL
Rhyolites are quartz-rich (silica rich) volcanic
rocks with abundant alkali feldspar (typically
sanidine) and lesser plagioclase. Rhyolites are a
volumetrically minor component of some volcanic
arcs and occur as vast ash flows in some areas
affected by tensional tectonics.