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Igneous Minerals. 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

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igneous minerals
Igneous Minerals
  • 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…
magma
Magma
  • Differntiate magma based on it’s chemical composition  felsic vs. mafic
melt composition freezing t
Melt Composition + ‘freezing’ T
  • 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
Back to silicate structures:

nesosilicates

phyllosilicates

sorosilicates

inosilicates

cyclosilictaes

tectosilicates

slide13

Liquid hot

MAGMA

Mg2+

Na+

Ca2+

Fe2+

O2-

O2-

O2-

O2-

O2-

O2-

Si4+

O2-

Si4+

O2-

O2-

Si4+

O2-

  • 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

rock

Mg2+

Fe2+

cooling

Mg2+

mineral structures

Mineral Structures

[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]

Silicates are classified on the basis of Si-O polymerism

mineral structures15

Mineral Structures

Chain Silicates – single and double

[SiO3]2- single chains Inosilicates [Si4O11]4- Double tetrahedra

pryoxenes pyroxenoids amphiboles

mineral structures16

Mineral Structures

Sheet Silicates – aka Phyllosilicates

[Si2O5]2- Sheets of tetrahedra Phyllosilicates

micas talc clay minerals serpentine

mineral structures17

Mineral Structures

Framework silicates – aka Tectosilicates

low-quartz

[SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates

quartz feldspars feldspathoids zeolites

characterizing minerals
Characterizing minerals
  • WITHIN classes (like the silicate classes) Minerals put into groupsbased on similar crystal structures differing typically in chemical substitution
    • Groups usually named after principle mineral
    • Feldspar group, mica group, feldspathoid group
  • Sites – designated M1, M2, etc. – designate spots where cations go into structure
    • different site designations have different characteristics (‘see’ different charge, have different sizes, etc.) and accommodate different ions based on this
equilibrium
Equilibrium
  • 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
Salty Ice cube experiment
  • 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