Microstructural and Mineralogical Changes on Heating Diaspore and Pyrophyllite

With a view to understanding the effect of heat on diaspore and pyrophyllite, as depicted by the assemblage of phases and microstructural changes, X-ray analysis and petrographic examination were carried out on the materials in the raw and fired states. The samples were obtained from the deposits in Jhansi area, Uttar Pradesh and were fired at temperatures of 1400°, 1500° and 1600°C.The mineralogical transformations in the bladed and granular varieties of diaspore and massive pyrophyllite were found to be very sluggish. The different stages were—gradual disruption of the parent texture, diffusion of some impurities, development of a glassy/intermediate phase, recrystallisation to corundum and mullite or mullite and cristobalite and growth thereof An increased temperature helped in attaining uniformity of texture.