Phase transitions and decomposition relations in calcic plagioclase
Phase transitions and decomposition relations in calcic plagioclase (in Real behavior in minerals; the integration of theory and technique, Anonymous)
American Mineralogist (February 1983) 68 (1-2): 41-59
A subsolidus temperature-composition diagram for the calcic portion of NaAlSi (sub 3) O (sub 8) -CaAl (sub 2) Si (sub 2) O (sub 8) is derived from: (a) compositions of plagioclase crystallized under a range of metamorphic conditions; (b) TEM observations of coexisting andesine and bytownite; and (c) TEM and crystallographic studies from the literature. Proposed existence of two tricritical points: one tricritical point is a consequence of the C1 (super -) <--> I (super -) transition; the other tricritical point is a consequence of the I1 (super -) <--> P1 (super -) transition. The C1 (super -) <--> I1 (super -) spinodal is responsible for two-phase intergrowths in labradorites and for BOeggild intergrowths (An (sub 45) -An (sub 65) ). The I1 (super -) <--> P1 (super -) spinodal is responsible for Huttenlocher intergrowths (An (sub 66) An (sub 87) ).--Modified journal abstract.
