Fourteen natural wairakite specimens from Japan were studied to evaluate the relationship between their lattice constants and their chemical composition. The lattice constants were determined using hkl indices which were assigned on the assumption that the monoclinic lattice of wairakite is closely related to that of analcime. Examination of the extinction rules indicated either Ia or 12/a as the possible space groups. Multicomponent regression analyses were carried out to evaluate the relationship between the chemical composition and the lattice constants. The parameters a, b, c, β, and V are expressed in terms of the numbers of sodium and silicon atoms and water molecules per unit cell as follows:
a(Å)=−0.0040 Na−0.0015 Si−0.0036H2O+13.8058b(Å)=0.0075 Na + 0.0009 Si+0.0021H2O+13.5723c(Å)=0.0148 Na+0.0021 Si + 0.0061H2O+13.3745β(∘)=−0.0939 Na+0.0262 Si + 0.0086H2O+89.6046V(Å3)=3.6122 Na + 0.1580 Si+0.7724H2O+2511.8682
The magnitudes of the standard deviations of the individual coefficients indicate that only the sodium content can be effectively predicted from the lattice parameters. The number of sodium atoms per unit cell can be estimated by the following equation:
Na = −15.8748(a−c)−16.4222(a−b)−3.3825β+310.0658±0.2495
Another equation which can be used for this purpose is based upon the observed values of 2θ° for CuKα1 radiation:
Na = −10.833{2θ∘(004)−2θ∘(400)}−8.933{2θ∘(040)−2θ∘(400)}+4.640±0.2832
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