Rapid Analysis of Silicate Rocks

Rapid methods are described for the determination of the major constituents in silicate rocks. Silica and alumina are determined spectrophotometrically on aliquots of a solution prepared by fusion of the sample with NaOH; a molybdenum blue method is used for Si02 ; and alizarin red-S is used in the determination of A1203. A second solution prepared by digestion of the sample with HF and H2S04 is used for the determination of TiOj, total iron, MriO, and P20s, by spectrophotometric methods. Ti02 is determined with tiron, total iron with orthophenanthroline, MnO as the permanganate, and P20s as molybdivanadophosphorie acid. Additional aliquots of the second solution are taken to determine CaO and MgO with an automatic photometric titrator using Versene (disodium ethylenediamine tetraacetate), the CaO being first precipitated before titrating the MgO. Another aliquot of the same solution is used for the determination of K20 and Na20 by flame photometer. FeO is determined by titration with K2 Cr20? after decomposition of a separate portion of sample with HF and HaSO*. Total H2O is determined by a modified Penfield method, and C02 is determined by measuring the volume of gas released by boiling a portion of sample powder with acid. Results of rapid analysis of twelve synthetic mixtures, two National Bureau of Standards standard samples, and two carefully studied silicate rocks are compared with the reported values.