Oxidation state and distribution of Fe in olivine from highly oxidized scoria and lava of Kasayama volcano, Hagi,Yamaguchi Prefecture

Abstract

Oxidation state and distribution of Fe in olivine oxidized at high temperatures were investigated. The samples of andesitic scoria and lava were collected from Kasayama volcano, Hagi, Yamaguchi Prefecture. The Fo contents of olivine in reddish black and black scoria are 83-85 and 79-81, respectively. The Fe²⁺:Fe³⁺ ratios in olivine of those scoria were 92-93:8-7 and 93-98:7-1, respectively. The Fo contents of olivine in reddish black and black lava were 79-80 and 73-80, respectively, and the Fe²⁺:Fe³⁺ ratios ranged from 92-99:8-1 and 93-99:7-1, respectively. On the basis of atomic contents at M1 and M2 and the Fe²⁺:Fe³⁺-ratio in olivine from the reddish black scoria, the chemical formula of the olivine was derived as [(Mg_0.835Fe²⁺_0.165)^M1 (Mg²⁺_0.830 Fe²⁺_0.053Fe³⁺_0.117)^M2]_Σ2.000Si_1.000O₄.