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Nilanjan Bhowmick AIR 3, CSIR NET (Earth Science)
- IIT JAM
- Geology (GG)
Which of the following rocks crystallises from water rich magma?
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Sajan sarthak Best Answer
Fluid in magma are very much effective in breaking the bond keeping the magma less viscous . Fluidsids can be Water , carbon dioxide, sulphur,chlorine . Option B,C are eliminated as they are viscous because they are having high sillica( sio2 content) .In magma Sio2 quantity determines the viscocity. Basaltic glass could also have been the answer but (glass is very fine grained means having lots of nucleation site but no grain is developed) so Granting pegmatite will be the answer pegmatite is a term related to big grains which satisfy the condition of mobility of ions to the nucleation site easily to form bigger crystal so less viscous.
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Rahul kumar
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Dissolved volatiles (H2O and CO2) under pressure depress the melting point of a minerals. Depression in melting point will lead to formation of coarse-grained minerals. Pegmatites generally formed from fluid rich magma remaining at the last stage of crystallization enriched in rare elements.
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Sajan sarthak
Fluid in magma are very much effective in breaking the bond keeping the magma less viscous . Fluidsids can be Water , carbon dioxide, sulphur,chlorine . Option B,C are eliminated as they are viscous because they are having high sillica( sio2 content) Basaltic glass could also have been the answer but because of less viscocity but that glass term indicates no proper development of grains . but granitic pegmatite clearly shows less viscocity so big grain development due to fast movement of ions to the nucleation site.