Tr_granite

Kanchenjunga (Nepal), Tourmaline both-mica Granite: Field width = 8.8mm A caption is in the bottom. The Image is XPL on mouse to PPL
カンチェンジュンガ（ネパール）の電気石両雲母花崗岩　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)．

A couple of decades ago, the sample was provided me by a member of the climbing party of Kyoto University for Mts.Himalaya. The difference between tourmaline and biotite is described at
http://www.alexstrekeisen.it/english/pluto/tourmaline.php

Tourmaline is distinguished from biotite and hornblende by the absence of cleavage, the presence of striated prisms, and (for hornblende) parallel extinction.

Change of absorption colour of tourmaline during the rotation of the microscope stage.
So, in this sample you can see in the left bottom, a beige color crystal under PPL, this is a tourmaline and other colored minerals are biotites. Two micas are seen in the center and the right hand side, colorfully under XPL. Also, another mica in the center shows direct extinction.

大昔に京都大学のヒマラヤ登山隊の方にいただいた．電気石と黒雲母はPPLで長さ方向を上下に置いたときに，鉱物の色の濃さが異なる．電気石は淡く，黒雲母は濃くなることで区別できる．また電気石はへき開が目立たない．このサンプルで，PPLで左下に見える褐色の鉱物は電気石，その他の有色鉱物は黒雲母．XPLにして中央と右に見えるカラフルな鉱物が白雲母．中央の別の白雲母はXPLで直消光を見せている．