Almandine-pyrope-grossular garnets: A method for estimating their composition using X-ray powder diffraction patterns

Calculated XRD powder patterns for several compositions in the Alm-Py-Gr ternary system were used to provide two identification diagrams for the composition of almandine-pyrope-grossular garnets. The first diagram is based on the changes of calculated Theta(332) (the diffraction angle of the 332 reflection) and of the intensity ratio of the 332 and 420 reflections (I-332/I-420). The second one is based on the changes of calculated Theta(444) and of the intensity ratio I-642/I-332. Six samples of natural garnets with different compositions determined by electron microprobe analysis were selected to check the reliability of the identification diagrams.