An incomplete reaction is frozen into this eclogite. The simple formula
for the reaction is:
omphacite --> diopside + plagioclase. The diopside and plagioclase grow
in alternate layers to produce symplectites. The symplectites grew in
lobes starting at the edge of a grain, and consumed omphacite as the
reaction proceeded towards the core of the original omphacite crystal.
Notice that the spacing of the intergrowths is thicker in the cores of the
symplectites than along their rims. This decrease in thickness indicates a
drop in temperature as the reaction proceeded. The reaction stopped when
the temperature got too cool.
Crossed polarizers with gypsum plate