Zircon Group ABO 4

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