Plagioclase: Albite-Anorthite series

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

No comments:

Post a Comment