Ionic SubstitutionIonic SubstitutionGoldschmidtGoldschmidt’’s Ruless RulesRadii differ by less than 15%Radii differ by less than 15%Charge difference of one unit substitutes as long asCharge difference of one unit substitutes as long aselectrical neutrality is maintained. Greater than oneelectrical neutrality is maintained. Greater than oneunit charge difference results only slight substitutionunit charge difference results only slight substitutionIon with higher ionic potential forms a stronger bondIon with higher ionic potential forms a stronger bondwith surrounding ionswith surrounding ionsEven when size and charge are satisfied, competingEven when size and charge are satisfied, competingions with different ions with different electronegativitieselectronegativities that form that formbonds of different ionic character may not substitutebonds of different ionic character may not substitutewellwellLarge Large LithophileLithophile Group (LIL) Group (LIL)Ions become sorted by size and chargeIons become sorted by size and chargeduring crystallization of a cooling magmaduring crystallization of a cooling magmaIons not fitting into the major rock formingIons not fitting into the major rock formingminerals are called incompatibleminerals are called incompatibleThese become enriched in the residualThese become enriched in the residualmagmamagmaElements in this category include:Elements in this category include:••KK++, , RbRb++, Cs, Cs++, Sr, Sr2+2+, Ba, Ba2+2+, REU, Zr, REU, Zr4+4+, Hf, Hf4+4+, Nb, Nb5+5+,,TaTa5+5+, Th, Th4+4+Greater charge difference results inGreater charge difference results inproblems maintaining electrical neutralityproblems maintaining electrical neutralityCoupled substitutionCoupled substitutionAdsorptionAdsorptionPartitioning between solid andPartitioning between solid andliquid characterized by:liquid characterized by:CamaflageCamaflageMinor elements has same charge andMinor elements has same charge andsimilar ionic radiussimilar ionic radiusExample ZrExample Zr4+4+ (0.80A) and Hf (0.80A) and Hf4+4+ (0.79A) (0.79A)ZrSiOZrSiO44ZrZr4+4+ and Hf and Hf4+4+ substitute equally well substitute equally wellPartitioning between solid andPartitioning between solid andliquid characterized by:liquid characterized by:CaptureCaptureMinor elements enter crystal preferentiallyMinor elements enter crystal preferentiallybecause of higher ionic potential then ions ofbecause of higher ionic potential then ions ofthe major elementthe major elementBaBa2+2+(1.44A) or Sr(1.44A) or Sr2+2+(1.21A) in place of K(1.21A) in place of K++(1.40A)(1.40A)in the feldspar latticein the feldspar latticerequires coupled substitution of Alrequires coupled substitution of Al3+3+ or Si or Si4+4+ to preserve to preserveelectrical neutralityelectrical neutralityPartitioning between solid andPartitioning between solid andliquid characterized by:liquid characterized by:AdmissionAdmissionEntry of foreign ion with lower ionic potentialEntry of foreign ion with lower ionic potentialthan the major ion results from lower chargethan the major ion results from lower chargeor larger radius, or bothor larger radius, or bothRbRb++(.157A) for K(.157A) for K++(1.46A) in feldspar(1.46A) in feldsparCaCa2+2+ by Sr by Sr2+2+ in calcite in calciteClCl-- for Br for Br-- in chlorides in chloridesDistribution Coefficient: DDistribution Coefficient: DD = D = CCxx/C/CllCCxx –– concentration of minor element in concentration of minor element incrystalcrystalCCll –– concentration of same minor element concentration of same minor elementin liquidin liquidD>1 D>1 –– capture captureD<1 D<1 –– admission admissionD=1 D=1 –– camaflagecamaflageDistribution CoefficientDistribution CoefficientDDAA = ( = (CCxxyy/C/Cllyy))AADDBB = ( = (CCxxyy/C/Cllyy))BBDDAA/D/DBB = ( = (CCxxyy))AA/(C/(Cxxyy))BB = K (constant) = K (constant)Can determine temperature dependenceCan determine temperature dependenceof minor element to enter A & Bof minor element to enter A & B(laboratory)(laboratory)Based on this the temperature of formationBased on this the temperature of formationcan be determined from the ratio of tracecan be determined from the ratio of traceelements in A & B in the elements in A & B in the