a) Shown below are textures of two magmatic rocks in Figures A and B. These rocks were produced by equilibrium crystallization of two separate melt compositions. An isobaric T-composition phase diagram in the system Mg2SiO4-S102 is shown in Figure C. Mineral abbreviations used in the Figures are as follows: Opx orthopyroxene, Qtz = quartz, Olv = olivine, Fo = Forsterite, En = Enstatite, Cr Cristobalite. L = Melt. PE1atmoSphere Opx OV L opxatz Opx Opx 1557 C Qt EnsL543 C Olv Fo+En En+cr Mg,Si,O, Sio PA Figure A Figure B Mg,Sio, Figure C Now answer the following questions. () Using the phase diagram in Figure C, write the nature of melt compos itions, which has given rise to these rocks. i) Which rock in the above Figures indicates final crystallization at point Y? (6- b) (1) Calculate the variance of the point X in Figure C. (ii) What is its petrological name?