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Igneous Minerals

Igneous Minerals

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Igneous Minerals

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  1. 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…

  2. Volcanic provinces

  3. Hot spots

  4. Basalt flows

  5. Plutons

  6. Intrusions

  7. Magma • Differntiate magma based on it’s chemical composition  felsic vs. mafic

  8. 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!

  9. Back to silicate structures: nesosilicates phyllosilicates sorosilicates inosilicates cyclosilictaes tectosilicates

  10. 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+

  11. 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

  12. Mineral Structures Chain Silicates – single and double [SiO3]2- single chains Inosilicates [Si4O11]4- Double tetrahedra pryoxenes pyroxenoids amphiboles

  13. Mineral Structures Sheet Silicates – aka Phyllosilicates [Si2O5]2- Sheets of tetrahedra Phyllosilicates micas talc clay minerals serpentine

  14. Mineral Structures Framework silicates – aka Tectosilicates low-quartz [SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates quartz feldspars feldspathoids zeolites

  15. 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

  16. 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

  17. 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