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Min Exam 3
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| Question | Answer |
|---|---|
| Neo(or Ortho)silicates | isolated Si tetrahedra (“island”) Ex: Olivine |
| Soro(or Di)silicates | Si2O7 groups (“bow ties”) Ex: Ebidote |
| Cyclosilicates | Rings of tetrahedra Ex: beryl or turmoline |
| Inosilicates | chains (double or single) of tetrahedra. Ex: pyroxines (sing) amphiboles (doub) |
| Phyllosilicates | sheets of tetrahedra. Ex: clay minerals, talc |
| Tectosilicates | framework of tetrahedra, linked throughout structure. Ex: quartz & feldspar |
| SiO2 polymorphs | Stishovite → Coesite → Low quartz --> High quartz → tridymite → Cristobalite |
| Stishovite | octahedral, also found in impact structures |
| Coesite | ultra high pressure (made in lab then found in meteor crater) |
| Low Quartz | 3 fold screw axis |
| High Quartz | truly hexagonal. 6 fold screw axis |
| Tridymite | hexagonal coordination (matching of rings). Looks like 2 stars of David stacked on one another |
| Cristobalite | isometric (insert analyzer, cross the polars, it stays dark) |
| pleochroism | in plain unpolarized light, it changes as you rotate the stage around |
| Microcrystalline varieties of SiO2 | Chalcedony (fibrous), Chert/flint (microcrystalline), jasper (red), tiger's eye (asbestos pseudomorph) |
| Opal | -SiO_2 * nH_2O -water varies between 3 & 10 percent -water or air in intersticial spaces -lined up silica spheres -not a fixed structure |
| Plagioclase feldspars | Oligoclase -> Andesine -> Labradorite -> Bytownite -> Anthorite |
| Alkali feldspars | Anthoroclase -> (Sanidine, Orthoclase, Microcline) |
| Potential for exsolution | higher temps are more tolerant of foreign cations. At lower temps those foreign cations form lamellae. |
| Miscibility gap | within this composition range at these temperatures, potash feldspar and albite crystalize together. |
| How the exsolution graph works | Liquidus at top, misc gap in middle (liq + sol), solvus at bottom. If it hits the solvus curve as it goes down, you more laterally and make exsolution |
| Amphibole | Double chain structure. [A][M4][M1-3][T]O22(OH)2 |
| Bowen's Discontinuous | Mg/Fe Olivine -> Orthopyroxene -> Clinopyroxene -> Amphibole -> Biotite -> (Alkali feldspar, muscovite, quartz) |
| Bowen's Continuous | Ca-rich Plag -> Na-rich plag -> (Alkali feldspar, muscovite, quartz) |
| Amphibole A site | Not always filled, but when it is it's usually Na or K. 10-12 coordinated. |
| Amphibole M4 site | 6-8 coordinated site. Always filled |
| Amphibole M1-3 site | 3 types of octahedral sites. Always filled. |
| Amphibole T sites | Usually Si8, but sometimes double substitutions happen |
| Substitution types | Simple (if the cations have the same charge). Couples (if they don't have the same charge, Al common) |
| Mica sheet structure | Sheets of tetrahedra link to form hexagonal gaps in between (not hex coord). OH sits in the middle of gap, at the same height as apical oxygen. |
| Mica sheet structure 2 | • All the tetrahedra in a given sheet are facing the same way • The overlapping oxygens at the bottom are in covalent bonds |
| 1:1 layer silicates | o TO TO TO (Tetrahedral sheet, octahedral sheet) o Van der Waals bonds holding them together (fairly week) o Ex: • Kaolinite Al2Si2O5(OH)4 – dioctahedral • Serpentine Mg3Si2O5(OH) – trioctahedral |
| 2:1 layer silicates (1) | o TOT TOT TOT (Tetrahedral sheet, octahedral sheet, tetrahedral sheet) o “TOT sandwich” o Van der Waals bonds o Ex: • Talc Mg3Si4O10(OH)2 - trioctahedral • Pyrophyllite Al2Si4O10(OH)2 - dioctahedral |
| 2:1 layer silicates (2) | o Cation in interlayer site (potassium) o Ex: • Muscovite KAl2(AlSi3)O10(OH)2 - dioctahedral • Phlogopite – trioctahedral • Biotitite KMg3(AlSi3)O10(OH)2 |
| 2:1 layer silicates (3) | o Cations + water in interlayer site o Ex: • Montmorillonite – dioctahedral • Vermiculite – trioctahedral |
| 2:1:1 layer silicates | o TOT O TOT o O in interlayer site o Ex: • Chlorite group minerals |
| Pyroxene (single chain) structure | -like amphibole but simpler -tetrahedra on a glide plane -only have M1s (between chains that point toward each other, octahedral site) -and M2s (between chains that point away from each other) -more limited subs -if they have Ts they're monoclinic |
| Olivine | -island silicate (tetrahedra not linked together) -M1 and M2, distinct octahedral sites -simpler than pyroxenes |
| Liquidus/solidus diagram for Olivine | • Mg2SiO4 on left, Fe2SiO4 on right • Loop oriented NW-SE -zoning is common due to this curve (swapping of calcium and sodium but also aluminum and silicon) Iron rich going toward edges, with Mg in middle is what youd expect in olivine. |
| A mineralogical “rule”: olivine and quartz don’t coexist | -continuum from MgO to SiO2. 33% is Forsterite 50% is Enstatite -in some granites maybe they’ll be together, if its iron rich and shallowly crystallizing, low pressure. |
| pressure temperature diagram for peridotite | • heat peridotite to melt and make basalt • or reduce pressure • the more common way is decompression melting |
| Spinel (MgAl2O4) | • cubic closest packing • 1/8 tetrahedral sites filled (Mg^2+) • ½ octahedral sited filled (Al^3+) |
| Mohorvic discontinuity | Partial melting above 200 -phase transitions below 200 • pyroxene -> garnet structure • olivine -> spinel -below 400 • spinel -> spinel structure -between 800 and 1000 • stishovite, ilmenite, and pervoskite type structures |
| most important minerals in rocks | -quartz -plagioclase -alkali feldspar -mica -clay -olivine -pyroxene -amphibole -garnet -calcite |
| Goldich's weathering series | -olivine -> pyroxene -> amphibole -> biotite -> potassium feldspar -> muscovite -> quartz • olivine least weather resistant • quartz most resistant -calcium plagioclase -> sodium plagioclase -> quartz |
| Textural immaturity | • much clay • grains not well sorted • grains not rounded • common in alluvial fans, fluvial overbanks, marine bathyl and abyssal, and neritic environments |
| Textural supermaturity | • little or no clay • grains well sorted • grains rounded • common in beaches and offshore bars, and eolian dunes |
| Sandstone triangle | -top quartz and chert -left corner – feldspar and all igneous rock fragments -right corner – mica, metamorphic rock fragments, and metaquartzite |
| Chert (microcrystalline SiO2) | • bedded – primary, deep water, derived from siliceous oozes • nodular – replacement, mainly in shallow water carbonates o silica dissolution, migration, reprecopitation o silica derived from detrital quartz, sponge spicules, microplankton skeletons |
| clay | sediment or rock composed dominantly of particles less than 0.002 mm |
| clay-sized | particles whose dimension is less than 0.003 mm |
| clay mineral | sheet silicate minerals that occur in the clay sized fraction of soils, sediments, sedimentary rocks, and weathered or altered rocks |
| Argillaceous | rock or sediment containing significant amounts of clay minerals |
| Main types of clay minerals | Kaolinite (1:1), Smectite group (2:1)(used in cat litter, shrink/swell), Illite (2:1), glauconite (2:1) |
| Why is limestone important? | -they preserve fossils -they can serve as a pH buffer -makes interesting landscapes (natural bridge, caverns) -can be a construction problem. -important aquifer -perhaps holding petroleum -construction material (pyramids, empire state building) |
| Dolomite formation | direct precipitation from seawater (lab), add Mg and remove Ca, fluid supplies both Mg and Carbonate |
| Aragonite | -orthorhombic -high pressure polymorph of calcite -reconstructive transformation |
| Sulfates | -common evaporate minerals (gypsum and anhydrite) -6 valence electrons |
| Barite (BaSO4) | -most common Barium containing mineral -radius ratios • Ba2+ = 1.42 A • O2- = 1.40 A -coordination is 12? -orthorhombic -light colored but high specific gravity -found in warm solutions |
| Gypsum | -most common sulfate -monoclinic -sheets of SO4 tetrahedra -Ca is 8 coordinated -varieties • satin spar • (investments of translucent) alabaster • selenite |
| Chlorides | • Halite – NaCl – rock salt • Sylvite – KCl – potash salts • Carnallite – KMgCl3 x 6H2O – potash salts |
| Apatite | -teeth have fluorapatite in them -hexagonal -strong bond between phosphorous and oxygen -fluroines . -common in many igneous and metamorphic rocks |
| Metamorphism | a mineralogical or textural change brought about in a rock in the solid state as a result of an increase in temperature or pressure |
| Order of metamorphosed shales (CanBitchGetStonedKiteSilly?) | chlorite, biotite, garnet, staurolite, kyanite, sillimanite. |
| shale contains | • clays (heat and pressure →) micas • quartz |
| basalt contains (heat and pressure →) greenstone | • olivine • plag • pyroxene |
| greenstone contains | • epidote • chlorite (sheet silicate) • actinolite (amphibole) |
| Metamorphic index minerals in Shales (add 50) | -Chlorite – 250-300 -Biotite – 400 -Garnet – 450 -Staurolite – 500 -Kyanite – 550 -Sillimanite – 600 |
| isograd | a line drawn on a map marking the first appearance of an index mineral |
| Porphiroblast | phenocryst in metamorphic rocks (larger crystal in a finer matrix) |
| Metamorphic facies | • a range of P-T conditions over which a particular common mineral assemblage or range of mineral assemblages is stable • for rocks metamorphosed under the same physical conditions, different mineral assemblages represent different bulk compositions |
| Serpentine | -H2O at apex -SiO2 at right corner • quartz -MgO at left corner -Brucite halfway between H2O and MgO -En halfway between SiO2 and MgO -Antigonite – Mg3Si2O5(OH)4 -Add water to peridotite (olivine and pyroxene) to make it serpentine |
| Asbestos | -strong -heat resistant -can weave it into things -same environment as talc |
| Asbestoform minerals | • Chystolite • Crocidolite • Amosite • Anthophylite • Tremolite • Actinolite |
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