Procedure for the Mineralogical Subdivision of Soil Separates by Means of Heavy Liquid Specific Gravity Separations

The application of petrographic, Xray, and chemical methods for the identification of the mineral constituents of soil material, particularly in the case of the finer separates, is unsatisfactory in many instances unless the various mineral species in the original material have been either isolated or concentrated to a considerable degree. This is especially true in the case of X-ray methods, for two reasons: First, a certain concentration of a crystalline material is necessary before its characteristic lines are recorded in the diffraction pattern. Jacob and co-workers (3) have found, for example, that clearly recognizable lines are not registered for montmorillonite unless this mineral constitutes at least ten per cent of the mixture under observation; second, there are instances where two or more distinct mineral species, when mixed, give patterns so nearly identical that they cannot be differentiated. Separation of the components of such a mixture would overcome these difficulties, and specific gravity methods appear to offer the most feasible line of attack. The purpose of this investigation was to further perfect a heavy liquid specific gravity procedure whereby the constituent minerals of soil separates, particularly those finer than 2.0 u, could be concentrated to such an extent as to facilitate their identification. Previous workers, using this type of procedure, have not generally been able to obtain consistently satisfactory results when working with material finer than 2.0 u in diameter, and a search of the literature revealed only one case (7) where material of particle size as fine as 0.3 u in diameter had been fractionated by specific gravity methods. The procedure herein described has been only recently developed and few data have been obtained thus far with it. However, sufficient progress has been made to justify a description of the technique employed.