Treatment of Analytical Data

6.2.3. Assigning Cations to Structural Sites

Using the normalized cation amounts, we finally may fill the cation sites in the minerals. Cations are assigned in the order shown in the table below for the structural formulae. For example, for amphibole, one first fills the T site, then the M123 site, then the M4 site, and finally, the A site. Site assignments are a subject of research and debate, and you may wish to use a different site filling scheme.

Mineral Site Assignments

Mineral	Formula	Site Assignments
Amphibole	A_0-1M4₂M123₅T₈O₂₂(OH)₂	T = Si,Al M123 = Al,Ti,Fe,Mg,Mn M4 = Na,Ca A = Na,K OH = F,Cl,OH
Andalusite	M₈Si₄O₂₀	M = Al,Cr,V,Fe,Mg,Ti,Na,Ca,K,Ga,Mn
Apatite	A₁₀(XO₄)₆(OH)₂	X = P,Si,V,As,S A = Ca,Sr,Ba,REE,Y,Na OH = F,Cl,OH
Biotite	A₁M₃T₄O₁₀(OH)₂	T = Si,Al M = Mg,Fe,Mn,Cr,Ti,Zn,V A = K,Na,Ba OH = F,Cl,OH
Carbonate	M₂(CO₃)₂	M = Ca,Mg,Fe,Mn,Sr
Epidote	A₄B₆(SiO₄)₆(OH)₂	A = Ca,REE,Sr,Y B = Al,Fe,Mn,V
Feldspar	A₁T₂Si₂O₈	T = Si,Al,Fe³⁺ A = Na,K,Ca,Sr,Ba,Rb,Pb,Eu
Garnet	X₃Y₂Z₃O₁₂	Z = Si,Al,Fe,Ti,P X = Mg,Fe,Ca,Mn,Y,Zn Y = Ti,Al,Fe,Cr,V,Sn,Zr
Kyanite	Si₁M₂O₅	M = Al,Cr,V,Fe,Mg,Ti,Ca,Na,K
Muscovite	A₁M₂T₄O₁₀(OH)₂	T = Al,Si M = Al,Mg,Fe,Mn,Li A = K,Na,Ca,Ba,Rb,Cs OH=F,Cl,OH
Olivine	M1₁M2₁Si₁O₄	M1 = Mg,Fe,Ni,Cr M2 = Ca,Mn,Mg,Fe,Ni,Cr
Pyroxene	M2₁M1₁T₂O₆	M1 = Al,Cr,Fe,Mg,Mn,Sc,Ti,V M2 = Ca,Na,Mn,Mg,Fe,Ni T = Si,Al
Sillimanite	Si₁M₂O₅	M = Al,Cr,V,Fe,Mg,Ti,Ca,Na,K
Sphene	Si₁M1₁M2₁(OH)₅	M1 = Al,Fe,Zr,Mg,Nb,Ta,V,Cr,Ti M2 = Mn,Na,REE,Y,Ba,Sr,Ca OH = F,Cl,OH
Spinel	A₁B₂O₄	A = Fe,Mg,Mn,Ni,Ti,Zn B = Al,Cr,Fe,Mg,Mn,Ti,V
Topaz	M₂T₂O₄(OH)₂	T = Si,Al,Ti M = Al,Fe,Mg,Ca OH = F,OH
Vesuvianite	A'₁₉Al₆AlFe₆B₁Si₁₈O₆₉(OH)₉	B = Mg,Fe AlFe = Al,Fe,Ti A' = Ca,K,Na OH = F,OH
Wollastonite	M₂T₂O₆	T = Si,Al,Fe M = Mg,Fe,Mn,Na,Ca,K
Zircon	Si₁M₁O₄	M = Al,Zr,Hf,Fe,Mg,Ti,Nb,Th,REE,Ca,Cu,Na,U,Mn,K,Y Si = Si,P

For analyses with F and/or Cl, we subtract the F and Cl values from the number for the OH-site to determine the OH content of the site. We can calculate the H₂O content of a minerals by multiplying the OH value by 9.0076 to get moles of H in the OH-site and dividing by the conversion factor. This number is added to analytical original total. The oxygen equivalents of F and Cl are calculated by multiplying moles of F by 0.4211 and moles of Cl by 0.2256, and the oxygen-equivalents for the F and Cl are subtracted from the analytical total.

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