3:00 PM - 3:15 PM
[R7-02] The coloration Factor of Pale Blue Sepiolite in amygdales in Higashimatsuura basalt from Kabeshima island, Saga Prefecture, SW Japan
[Presentation award entry]
Keywords:Kabeshima Island, sepiolite, copper, alkali basalt
The alkali basalts known as the Higashi-Matsuura basalts are widely distributed on Kabeshima Island, Yobuko area, Saga Prefecture, and pale blue sepiolite has been found in amygdales in the Higashi-Matsuura basalts on the island. A white to light-green sepiolite has been reported previously in Higashi-Matsuura basalts from near Karatsu city (Ishibashi, 1974), but not the sepiolite with a pale blue color. In this study, to investigate of color of the pale blue sepiolite, we analyzed the pale blue sepiolite chemical composition using EPMA, LA-ICPMS and TEM-EDS.
The amygdale minerals in the alkali basalt consist of sepiolite, ilmenite, calcite, Mn oxides and chlorite-like mineral. The pale blue sepiolite has a spongy texture with pores less than 0.5 µm in diameter on the mineral surface and occurs in radial clusters 5-10 µm thick on a yellowish-brown chlorite-like mineral. Quantitative analysis of the pale blue sepiolite showed that it consists mainly of 46.48 wt.% SiO2, 16.89 wt.% MgO, and 4.69 wt.%Al2O3. The trace transition-metal elements detected in the pale blue sepiolite in microscale chemical analysis using LA-ICPMS that might cause coloration in sepiolite are 0.403 wt.% Mn, 0.392 wt.% Fe3+, 0.145 wt.% Cu, 0.036 wt.% Ti, 0.012 wt.% Cr and 0.010 wt.% Ni. However, Fe and Mn are not detected in the nano scale chemical analysis of sepiolite using TEM-EDS. Therefore, Fe and Mn detected in microscale chemical analysis are likely to be due to contamination with other minerals that coexist with the sepiolite, such as Mn oxides and chlorite-like mineral, with Cu being the most abundant transition metal element in the sepiolite.
The result of this study suggests that the transition-metal element Cu is responsible for the pale blue color of the sepiolite. However, Further research is needed to determine whether sepiolite which crystal lattice Cu-containing exhibits pale blue color, because it is no report on the color of Cu bearing sepiolite.
The amygdale minerals in the alkali basalt consist of sepiolite, ilmenite, calcite, Mn oxides and chlorite-like mineral. The pale blue sepiolite has a spongy texture with pores less than 0.5 µm in diameter on the mineral surface and occurs in radial clusters 5-10 µm thick on a yellowish-brown chlorite-like mineral. Quantitative analysis of the pale blue sepiolite showed that it consists mainly of 46.48 wt.% SiO2, 16.89 wt.% MgO, and 4.69 wt.%Al2O3. The trace transition-metal elements detected in the pale blue sepiolite in microscale chemical analysis using LA-ICPMS that might cause coloration in sepiolite are 0.403 wt.% Mn, 0.392 wt.% Fe3+, 0.145 wt.% Cu, 0.036 wt.% Ti, 0.012 wt.% Cr and 0.010 wt.% Ni. However, Fe and Mn are not detected in the nano scale chemical analysis of sepiolite using TEM-EDS. Therefore, Fe and Mn detected in microscale chemical analysis are likely to be due to contamination with other minerals that coexist with the sepiolite, such as Mn oxides and chlorite-like mineral, with Cu being the most abundant transition metal element in the sepiolite.
The result of this study suggests that the transition-metal element Cu is responsible for the pale blue color of the sepiolite. However, Further research is needed to determine whether sepiolite which crystal lattice Cu-containing exhibits pale blue color, because it is no report on the color of Cu bearing sepiolite.