Chemistry of Blotites from Pelitic Schists and Granitic Rocks of McCluskieganj, District Palamau, Bihar

Composition of biotites from the pelitic schists and granitic rocks of McCluskieganj indicate that the former is rich in magnesium and the latter in iron; their Mg-Fe content is controlled by the composition of the respective host rock. The study of biotite of granitic rocks suggests that oxygen fugacites which prevailed during crystallization closely followed the QFM buffer. Positive correlation of Na between the co-existing K-feldspar and biotite in the granitic rocks, indicates that equilibrium conditions had reached during crystallization of these minerals. Experimental results of a porphyritic granite show that the rock was formed at the 'minimum melt' condition (655°C at PH₂0 = 4 kb).