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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

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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

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