Chemical Composition of Lava Flows : I. Iron Content of the Lava Flow Erupted in 1950〜1951 from Volcano O-sima, Izu, Japan

Abstract

Systematic sampling in the lava flow erupted in 1950～1951 from Volcano O-sima was carried out in order to ascertain whether such a large lava flow has uniform chemical composition or a certain regularity in it. After the error of chemical analysis was determined, the sampling and the preparation of sample for chemical analysis from it was criticized by the iron content of 159 samples collected from the lava flow and the following conclusion was obtained. 1) This lava flow has very uniform total iron content, Fe₂O₃^* = 14.2～14.4, average 14.3%, and distinct difference of the total iron content from other lava flow or rocks erupted in other ages. Any distinct regular difference could not be found among their total iron contents of each part of this lava flow regardless their appearance of rocks samples such as red coloured, porous, scoriaceous, etc. 2) Fe₂O₃/FeO ratio in this lava flow varies distinctly owing to the degree of oxidation during the solidification of it and is larger in the samples of red colour, porous structure, and scoria, or stalactitic structure than normal compact samples. Any regular difference in the Fe₂O₃/FeO ratio could not be found among the 159 samples collected in this lava flow and other rocks erupted in other ages. 3) About 4g of rock sample was sufficient for the determination of the total iron content in this lava flow when about 4g of rock sample was completely pulverized. 4) One or two samples of about 10g is sufficient for the determination of the total iron content of this lava flow.