Term
| The higher the Coordination Number... |
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Definition
| ...the further apart the anions are from the cation. Therefore, the electron cloud of the cation expands slightly to fill the space |
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Term
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Definition
| 3D frameworks of fully polymerized SiO2 tetrahedra (quartz, feldspars, feldspathoids, zeolites) |
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Term
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Definition
| Independent SiO4 tetrahedra (garnet, olivine) |
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Term
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Definition
| [Si2O7]6- double tetrahedra (lawsonite) |
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Term
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Definition
n[SiO3]2- n=3, 4, 6
form hexagonal framework of tetrahedra (beryl) |
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Term
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Definition
Tetrahedral chains
[SiO3]2- single chains: pyroxenes
[Si4O11]4- double chains: amphiboles |
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Term
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Definition
| [Si2O5]2- Sheets of tetrahedra (micas, talc, clay minerals, serpentine) |
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Term
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Definition
Forsterite: Mg2SiO4
Fayalite: Fe2SiO4 |
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Term
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Definition
Pyrope: Mg3Al2(SiO4)3
Spessartine: Mn3Al2(SiO4)3
Almandine: Fe3Al2(SiO4)3 |
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Term
| Paragenesis of different olivine chemistry (dominantly Forsterite and Fayalite) |
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Definition
Olivine occurrence:
principally in mafic and ultramic igneous and meta-igneous rocks
Fayalite in meta-ironstones and in some alkalic granitoids
Forsterite in some siliceous dolomitic marbles |
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Term
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Definition
| A phenomenon in which one or more ions can substitute in a mineral's structure without significantly changing the mineral's stability or symmetry |
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Term
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Definition
Pyrope: typically the dominant aluminum-bearing phase in peridotites at high pressure
Almandine common in evolved igneous rocks, such as granites; also present in metamorphic rocks having granitic bulk compositions
Grossular: common in skarn metamorphic rocks, containing high amounts of Ca
Spessartine: found mostly in pelitic metamorphic rocks where Mn contents are high |
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Term
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Definition
| Single-chain inosilicates with I-beams facing the same direction (+ or -) |
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Term
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Definition
| Single-chain Inosilicates with I-beams facing alternating directions |
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Term
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Definition
| double-chain inosilicate with I-beams facing same direction (+ or -) |
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Term
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Definition
| double-chain inosilicate with I-beams facing alternating directions |
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Term
| Clinopyroxene unit cell and why |
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Definition
| Tetrahedral chain above M1 octahedral sites is offset from that below, forming a monoclinic unit cell |
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Term
| Orthopyroxene unit cell and why |
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Definition
| Offsets resulting from alternating (+) and (-) I-beams compensate for each other, forming an orthorhombic unit cell |
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Term
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Definition
Can tell by cleavage angles:
90º angles=pyroxene(narrow single-chain I-beams)
60-120º angles=amphibole(wider double-chain I-beams) |
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Term
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Definition
W1-p(X,Y)1+pZ2O6
W=Ca, Na
X=Mg, Fe2+, Mn, Ni, Li
Y=Al, Fe3+, Cr, Ti
Z=Si, Al
Pyroxenes are anhydrous, so high-temperature or dry conditions favor pyroxenes over amphiboles |
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Term
| General Amphibole formula |
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Definition
W0-1X2Y5[Z8O22](OH, F, Cl)2
W=Na, K
X=Ca, Na, Mg, Fe2+ (Mn Li)
Y=Mg, Fe2+, Mn, Al, Fe3+, Ti
Z=Si, Al |
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Term
| CN's of Amphibole formula |
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Definition
W0-1: CN=10-12 "vacant" or occupied by Na or K
X2: CN=6-8 M4 site occupied by Ca, Mg, Fe2+, and Na
Y5: CN=6 M1, M2, M3 sites occupied by mg, Fe2+, and Al
Z: CN=4 mostly Si, some Al |
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Term
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Definition
| based on interconnected six member rings of SiO4 tetrahedra that extend outward in infinite sheets. 3/4 oxygens from each tetrahedra are shared with other tetrahedra. Most contain OH-, centered inside the ring. |
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Term
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Definition
trioctahedral sheet silicates where each O or OH is surrounded by 3 divalent cations (Mg2+ or Fe 2+)
Dioctahedral sheet silicates where each O or OH ion is surrounded by 2 divalent cations (usually Al +3) |
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Term
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Definition
when Mg-rich silicates (pyroxene, olivine) are hydrated
2Mg2SiO4 + 3H2O--> Mg3Si2O5(OH)4 + Mg(OH)2
olivine water serpentine brucite |
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Term
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Definition
| requires Mg-rich environment. Therefore found in low grade metamorphic rocks that originated as ultrabasic to basic igneous rocks. |
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Term
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Definition
White micas: muscovite, paragonite, margarite (trioctahedral group)
Black/brown mica: Biotite (dioctahedral group)
Biotite and Muscovite most common micas |
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