Rapakivi

Muran coast (Hokkaido) Cordierite tonalite: Field width = 8.8mm A caption is in the bottom. The Image is XPL on mouse to PPL
ムーラン海岸（北海道）菫青石トーナライト　横幅8.8mm．写真の下に説明．薄片写真：クロスポーラー（XPL)．マウスを乗せるとオープンポーラー（PPL)．

This sample contains cordierites. However, the identification of them is very difficult,
Distinguishing Features;

Resembles quartz, bur more distinctly blue. Corundum is harder. Twinned cordierite resembles plagiclase in thin section, but plagioclase has more distinct cleavage and lacks radial twinning. Yellowish, pleochroic halos around radioactive minerals such as zircon are quite common. Typically contains small, opaque inclusions. Hardness = 7.

http://www.science.smith.edu/geosciences/petrology/Petrography/cordierite/cordierite.html

北海道日高南部のムーラン海岸に露出する菫青石トーナライト．菫青石は石英や長石との見分けが難しい．上記英文参照．