Is Talc distinctive of a given metamorphic facies? If yes,Why?

Metamorphic facies are usually defined in terms of equilibrium
*assemblages* of minerals that form in rocks of a given composition at
a given temperature and pressure.  (As defined by Fyfe and Turned in
1966, a metamorphic facies is "A set of metamorphic mineral
assemblages, repeatedly associated in space and time, such that there
is a constant and therefore predictable relation between mineral
composition and chemical composition.")  Rocks of different
composition will have different equilibrium mineral assemblages at a
specified T and P, and the set of all those assemblages define a
"facies".  Singling out one mineral as being "distinctive" of a facies
isn't really in keeping with this definition.

Talc is a common metamorphic mineral that forms in both metamorphosed
carbonate sediments and metamorphosed (hydrated) ultramafic rocks.  It
is stable from rather low temperatures (~400C) in greenschist facies
rocks, up to quite high temperatures (>800C) in granulite facies
rocks.  In metacarbonates, the range of bulk rock compositions over
which talc is stable becomes increasingly restricted (to more
magnesian compositions) as one goes up in temperature.  There is a
nice set of phase diagrams at
http://www.uwgb.edu/dutchs/PETROLGY/barrcarb.HTM illustrating this.

i was a bit confused by this question too. didn't really know how a
mineral can be distinctive of a facies. But ur link is very
helpful....so thanks. u rock!!!