Forsteritic Determination of Olivine by XRD Analysis

Abstract

<p> Fo. determinative curves for lattice planes (301), (311), and (401) were calculated from four natural olivines. 2θ values for each olivine were computed from the lattice parameters using the reciprocal lattice d* for the orthorhombic crystal system d*hkl = [h^2/a^2 + k^2/b^2 + l^2/c^2]^1/2 combined with the Bragg equation λCuKα = 2 sin θhk / d*hkl </p> <p> XRD patterns for 10 natural olivines were used to determine their respective Fo. composition. Errors were calculated for the Fo. composition of the natural olivines yielding an accuracy from the determinative curves of± 6 wt. % Fo. An olivine of 90 wt. % Fo. was X-rayed and plotted along the determinative curves giving values of Fo. composition for (301), (311) and (401) of 89, 87 and 85 wt. % respectively.</p> <p> The effect of Ni, Mn and Ca substituting into the (Mg, Fe) olivine structure causing Δ2θ shifts was also considered and found to be negligible for natural (Mg, Fe) olivines.</p>