Download Chapter 8: Major Elements

Igneous Minerals
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We will be discussing and working in lab with
the major igneous minerals and common
accessory minerals
We will look at putting these minerals together
into rocks and ways to identify and characterize
those rocks
Gain a sense of what the minerals and the rocks
they form tell us about the earth…
Volcanic provinces
Hot spots
Basalt flows
Plutons
Intrusions
Magma
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Differntiate magma based on it’s chemical
composition  felsic vs. mafic
Melt Composition + ‘freezing’ T
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Liquid magma freezes into crystals  the
composition of what freezes first is governed by the
melt’s composition
Analogous to the composition of seawater ice 
icebergs are composed of pure water; pure water
freezes first, leaving the concentrated brine behind
In magmas  More silica = lower T; more Ca,
Mg=higher T
Silica polymerization also affected by T and how
much Si there is!
Back to silicate structures:
nesosilicates
phyllosilicates
sorosilicates
cyclosilictaes
inosilicates
tectosilicates
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Ca2+
O2Si4+
O2-
Mg2+
Na+
Fe2+
Liquid hot O2MAGMA
2O
O2- Si4+ O2- O2O2- O2- Si4+
Discontinous series –
Structures change,
harder to re-equilibrate
Continuous Series 
plag re-equilibrates
quicker and if not is a
continuum in
composition rather than
a change in mineral as T
decreases
Mg2+
O2-
cooling
rock
Mg2+
Fe2+
Mineral Structures
Silicates are classified on the basis of Si-O polymerism
[SiO4]4-
Isolated tetrahedra Nesosilicates
Examples: olivine garnet
[Si2O7]6-
Paired tetrahedra
Sorosilicates
Examples: lawsonite
n[SiO3]2- n = 3, 4, 6
Ring silicates
Cyclosilicates
Examples: benitoite BaTi[Si3O9]
axinite Ca3Al2BO3[Si4O12]OH
beryl Be3Al2[Si6O18]
Mineral Structures
Chain Silicates – single and double
[SiO3]2- single chains
pryoxenes pyroxenoids
Inosilicates
[Si4O11]4Double tetrahedra
amphiboles
Mineral Structures
Sheet Silicates – aka Phyllosilicates
[Si2O5]2Sheets of tetrahedra
micas talc clay minerals serpentine
Phyllosilicates
Mineral Structures
Framework silicates – aka Tectosilicates
low-quartz
[SiO2]
quartz
3-D frameworks of tetrahedra: fully polymerized
feldspars feldspathoids zeolites
Tectosilicates
Characterizing minerals
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WITHIN classes (like the silicate classes)
Minerals put into groups based on similar crystal
structures differing typically in chemical
substitution
Groups usually named after principle mineral
 Feldspar group, mica group, feldspathoid group
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Sites – designated M1, M2, etc. – designate spots
where cations go into structure
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different site designations have different characteristics
(‘see’ different charge, have different sizes, etc.) and
accommodate different ions based on this
Equilibrium
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Need a description of a
mineral’s equilibrium
with it’s surroundings
For igneous minerals, this
equilibrium is with the
melt (magma) it forms
from or is a representation
of the Temperature and
Pressure of formation
Salty Ice cube experiment
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Thought experiment: Put pure H2O ice cube
into salty water, let it sit for a certain time and
look at the distribution of salt inside the ice
cube
When the ice cube reaches a point where the
concentration of salt is the same through the
whole ice cube it has reached equilibium