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Zircon Group ABO 4. Presented by Joyleen Desai. Zircon Occurrences. Zircons are found in igneous, sedimentary, and metamorphic rocks They are found in mantle xenoliths, lunar rocks, meteorites, and tektites - PowerPoint PPT Presentation
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Zircon GroupABO4
Presented byPresented byJoyleen DesaiJoyleen Desai
Zircon Occurrences
Zircons are found in igneous, sedimentary, Zircons are found in igneous, sedimentary, and metamorphic rocksand metamorphic rocks
They are found in mantle xenoliths, lunar They are found in mantle xenoliths, lunar rocks, meteorites, and tektitesrocks, meteorites, and tektites
Zircons can survive one or more cycles of Zircons can survive one or more cycles of erosion, sedimentary transport, diagenesis, erosion, sedimentary transport, diagenesis, and/or low grade metamorphismand/or low grade metamorphism
Zircon Structure
ZrSiOZrSiO44 II4411//amd amd Z=4Z=4 Naturally occurring dimorphNaturally occurring dimorph
ZrSiOZrSiO44 II4411//a a Z=4Z=4 High P polymorphHigh P polymorph Scheelite structure ~11% more denseScheelite structure ~11% more dense Unknown in natureUnknown in nature
Zircon Structure
AtomAtom SiteSite MultiplicityMultiplicity Positional Positional ParametersParameters
Site Site SymmetrySymmetry
ZrZr aa 44 0, 3/4, 1/80, 3/4, 1/8 4422mm
SiSi bb 44 0, 3/4, 5/80, 3/4, 5/8 4422mm
OO hh 1616 0, 0, xx, , zz mm
Reference: Speer (1980)
Other Minerals Having the ABO4 Zircon Structure
Hafnon HfSiOHafnon HfSiO44
Xenotime YPOXenotime YPO44
Behierite (Ta,Nb)BOBehierite (Ta,Nb)BO44
Thorite ThSiOThorite ThSiO44
Coffinite USiOCoffinite USiO44
Zircon ChemistryElements substituting for Zr(A) and Si(B)
in zircon (ABO4)
Thermal Expansion
The bulk thermal expansion coefficient (α) The bulk thermal expansion coefficient (α) = 4-5 x 10= 4-5 x 10-6-6//°C (25-1300°C)°C (25-1300°C)
Relatively insensitive to thermal shockRelatively insensitive to thermal shock
Compression Zircon has the highest bulk modulus (234 GPa) Zircon has the highest bulk modulus (234 GPa)
of any measured substance with tetrahedrally of any measured substance with tetrahedrally coordinated Sicoordinated Si
Si bulk modulus = 230 Si bulk modulus = 230 ++ 40 GPa 40 GPa Anonymously compressibleAnonymously compressible
Zr bulk modulus = 280 Zr bulk modulus = 280 ++ 40 GPa 40 GPa Unusually incompressibleUnusually incompressible
cc axis ~ 70% more compressible than axis ~ 70% more compressible than aa
Transformations
Inclusion Chemistry
Inclusions as Indicators of Early Earth Environments Inclusions contained in igneous zircons Inclusions contained in igneous zircons
typically reflect the parent melttypically reflect the parent melt δδ1818O values of Hadean zircons indicate that O values of Hadean zircons indicate that
oceans, continental crust, and a sedimentary oceans, continental crust, and a sedimentary cycling process were all present by 4.3 Gacycling process were all present by 4.3 Ga
ffOO22 values can theoretically be determined values can theoretically be determined via knowledge of the Fevia knowledge of the Fe3+3+/Fe/Fe2+2+
ratioratio