Certain metamorphic minerals are only stable for a limited range of pressure and
ID: 121411 • Letter: C
Question
Certain metamorphic minerals are only stable for a limited range of pressure and temperature conditions. Assemblages (groups) of minerals may form under even more limited conditions. a) On the diagram below, which star represents a set of pressure (P) and temperature (T) conditions at which silimanite (Sil) and kyanite (ky) can co-exist? b) On the diagram below, which star represents a set of P and T conditions at which staurolite (St) will be stable but garnet (Gt) will not? c) Not all rocks metamorphosed under these conditions will contain these two minerals. Why not?Gt St St Ky 10 Sil Cld minerals. Why not?5 Chl Gt And St Sil And 400 600 700 800
Explanation / Answer
whenever some rocks goes under metamorphism due to the effct of pressure and temperature theeir properties and characterstics has been changed and they converted into other minerals and rocks . some rocks amd minerals need particular range of pressure and temperature fo their formation and they only can stable at that PT conditions if intensity of PT condition wil increase then minerals or rocks will also change with it. these particular zones of PT conditions is also called metamorphic facies in which selected mineral assemblages are formed like zeolite facies which is low grade metamorphism and the zeolites , choroite, muscovite, and quartz are mainly include in this facies. on other hand , in granulite facies which represents higher temperature condition and mineral assemblages are plagioclase, hypersthene, garnet and diopside. like that at different temperatude pressure conditions different minerals formed.
a. kyanite + silliminite both occurs commonly at the the moderate to high PT conditions at the regional metamorphism, silliminite formed at the higher temperature than kyanite and its a polymorph of the kyanite. in a diagram green star indicate the PT condition which familiar for the kyanite and silliminite .
b. staurolite formed and can stable at the moderate pressure and moderate to higher temperature but garnet cant stable at the higher temperature so here blue star will be represent the condition where staurolite can stay but not garnet.
c. not all metamorphosed rocks contain those minerals in these PT conditions because for the formation of the mineral it needed a chemical and solution or material with the particular conditions . some rocks dont have enough material or solution to make minerals thats why some rocks dont have mierals who metamorphosed into these conditions due to lack of essential material.