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Tectosilicates

Tectosilicates. Why are they important?. They make up ¾ of the rocky crust of the earth—all oxygen anions are shared with neighboring tetrahedra. SiO 2 Group. Quartz both low and high Tridymite Cristobalite Stishovite and Coesite Opal. Feldspar Group. K-spar Microcline Orthoclase

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Tectosilicates

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  1. Tectosilicates

  2. Why are they important? • They make up ¾ of the rocky crust of the earth—all oxygen anions are shared with neighboring tetrahedra

  3. SiO2 Group • Quartz both low and high • Tridymite • Cristobalite • Stishovite and Coesite • Opal

  4. Feldspar Group • K-spar • Microcline • Orthoclase • Sanidine • Plagioclase • Albite to Anorthite

  5. Zeolites • Framework silicates with both SiO4 and AlO4 tetrahedra • They are common in the volcanic rocks along the North Shore

  6. Zeolites • There are chain-like structures whose minerals form acicular or needle-like prismatic crystals, ie natrolite. • Sheet-like structures where the crystals are flattened platy or tabular with usually good basal cleavages, ie heulandite. • And framework structures where the crystals are more equant in dimensions, ie Chabazite.

  7. Natrolite— Na2[Al2Si3O10]·2(H2O)

  8. Heulandite (Ca,Na)2-Al3(Al,Si)2Si13O36·12(H2O)

  9. Chabazite (Ca0.5,Na,K)4[Al4Si8O24]·12(H2O)

  10. Ok, What did the formulas of zeolites have in common? • All had a large amount of water in their structures • What do you think this means for their specific gravities?

  11. Feldspathoid • These are feldspar like minerals that are deficient in SiO2 • Leucite KAlSi2O6 • Nepheline NaAlSiO4 • Sodalite Na8Al6Si6O24Cl2 • Lazurite (Na, Ca)8Al6Si6O24(S, SO4) • Lapis Lazuli

  12. Let’s go back to the quartz group

  13. Quartz • What can you tell me about the mineral quartz? • Physical properties • Optical properties • Where do we find it?

  14. Some other varieties of Quartz • Amethyst • Rose • Smokey • Citrine • Milky • Tiger-eye

  15. Microcrystalline • Fibrous • Chalcedony –agate and onyx • Granular • Flint, chert, jasper

  16. Onyx

  17. Alkali Feldspars • Sanidine • Microcline • Orthoclase • Albite • Perthite (ab in kspar) • Antiperthite (kspar in ab)

  18. Orthoclase • Commonly twinned • Carlsbad • Manebach

  19. Carlsbad

  20. Manebach • Simple twin on 001

  21. How do you tell the Kspar’s apart? • Make a list on the board

  22. Plagioclase Series • Peristerite An 2-15 • Labradorite An 47-58 • Albite, Oligoclase, Andesine, Labradorite, Bytownite, Anorthite

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