P=1 atm
Composition of 1st crystal
X
Equilibrium Crystallization of the Plagioclase Feldspars
1. Liquid of
composition X (An61) cools to the liquidus
2. Crystals of approximately An87 begin to form
3.
Crystals have higher Ca/Na than liquid; ppt of crystals causes L composition to become more sodic.
4.
Ratio of Ca/Na in both crystals
and liquid decrease with
decreasing temperature;
proportion of crystals increases
as liquid decreases
Composition of last crystal
Composition of last liquid
5. Crystals of An61 cool without further change in composition
PowerPoint® presentation by
Kenneth E. Windom