A new method for separation of cristobalite and tridymite particles from rocks containing them.

Abstract

To quantify the free silica in a working environment by phosphoric acid method, a few grams of the standard free silica powder is necessary. It is, however, not easy to prepare the amount of the powder in the laboratory because they are usually found in a small phenocryst in some volcanic rocks. A new method for separation of cristobalite and tridymite particles from mother rocks is developed by using hot phosphoric acid with heavy liquid and very effective. It is known that most part of free silica particles survives in a hot phosphoric acid, while silicate particles are dissolved in the acid1)2)3). It is, therefore, expected that the acid residue is formed of the particles of a few sorts of free silica min-erals, and that some of these particles can be separated from the acid residue with the help of heavy liquid4). Present paper shows a new trial on preparation of the cristobalite or tridymite particles from the mother rocks by combination of pho-sphoric acid method and heavy liquid method.