Estimation of clay proportions in mixtures by X-ray diffraction and computerized chemical mass balance: Clays & Clay Minerals 32

Abstract--As part of a laboratory study of the hydrothermal teration of kimberlite, a mass balance procedure has been developed for estimating the relative proportions of synthetic phyllosilicate phases--chlorite, vermiculite, smectite, kaolinite and serpentine--present in reaction products. The procedure is based on a combination of X-ray powder diffraction (XRD) measurements (for phase identification), atomic absorption determinations (for total Si, A1, Fe, and Mg) and published analyses of clay minerals (for stoichiometric deductions). It centers on the computer inversion of a 4 x 4 matrix form of four simultaneous equations representing the mass balance of Si, A1, Fe, and Mg in four chosen minerals and incorporates a systematic routine for selecting from all possible permutations ofhigh and low estimates of the mineral chemical analyses acceptable sets of product stoichiometries and phase proportions con-sistent with the total metal analyses. To minimize uncertainties and computing time, the program takes account of elemental relationships and water mass balances associated with phyllosilicates. It also ac-commodates data relevant to poorly crystalline phases for which a range of theoretical type-analyses modeled on aluminum oxyhydroxides and 9-1 l-A, 2:1 layered aluminosilicates are employed. The procedure produces reliable trends in phase proportions consistent with the intensities of char-acteristic XRD peaks of clay minerals present in the analyzed mixture; for example, increases in estimated kaolinite proportions correspond with larger 7-/k (and other) peaks in analyzed samples. A precision of 7-25 % has been routinely achievable