Albite-Anorthite
nα=1.527 - 1.577
nβ=1.531 - 1.585
nγ=1.534 - 1.590
δ=0.007 - 0.013
2V (plutonic/low):
Anorthite-'Bytownite': -(75-90)°
'Labradorite': +(80-90)°
'Oligoclase30-15': -(85-90)°
'Oligoclase15-Albite': +(78-90)°
Maximum extinction angle of fast ray to albite twinning in section cut perpendicular to (010) for high/low (volcanic/plutonic) plagioclase
Thin section photos:
Plagioclase phenocryst from andesite.Kamchatka Peninsula. XPL |
Albite crystal in microcline matrix. The Kola Peninsula, Russia. The white bar is about 1mm, XPL. |
Zoned crystal of plagioclase with altered core. Alaska, USA. Zoom 40x |
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