[frethack (OP)]

Okay...Im trying to finish a lab.

A couple of question:

Is the name for a mineral that is 50% Jadeite and 50% Diopside called Omphacite? (Its a continuous series, but the book is not very clear)

Also, is the mineral that limits the stability of quartz at high pressures Enstatite?

One more...does Forsterite limit the stability of Jadeite?

[Bass]

It depends.  How's that for a definitive answer?

My dim recollection is that Omphacite is part of the Jadeite-Diopside continuous series.  Omphacite (according to my decades old petrology notes), represents anything from 25% to 75% Jadeite in the series.  Got a couple of good samples from eclogite I collected in CA.

Also have studied a specimen of coesite, which is a high pressure form of quartz- estimated formation around 20 kb.  From a meteorite impact site.  Add a spot of heat and throw in a bit of Fe, Mg & Ca and enstatite will consume most of the free silicon.  But this is really more a thermodynamics problem than a mineralogical problem.

As to your last question- that again is more of a thermodynamic question.  Does the system contain albite?  or anorthite? enstatite?

Is this for metamorphic petrology? or just curiosity?

[frethack (OP)]

Yeah, for metamorphic petrology (good guess)!

And the system does contain albite

Your answers have already been helpful!

[JimBob]

This is why I choose structural geology and sedimentology.