THERMAL-BEHAVIOR OF FIBROUS ZEOLITES OF THE NATROLITE GROUP

The western region of the Deccan Volcanic Province (DVP) is constitute d of tholeiitic lava I flows. They host numerous cavities, varying in size and shape, largely occupied by zeolites and a variety of secondar y minerals, amongst which the fibrous zeolites (natrolite group), are particularly gorgeous and attractive. Scolecite and mesolite are the o nly two members commonly occurring in this region. Our data on their t hermal behaviour significantly differs from that reported in previous literature. Scolecite, Ca-8(Al16Si24O80).24H(2)O shows three distinct steps instead of two and water loss is observed even beyond 550 degree s C. It is held that the first step corresponds to the expulsion of wa ter from the site farthest away from Ca and the next two steps in succ ession correspond to the two sites nearer to Ca. Mesolite, Na16Ca16(Al 48Si72O240).64H(2)O has much more complex behaviour with four or five steps of water expulsion and a major loss around 248-270 degrees C in a double reaction attributed here to the expulsion of water from scole cite type channels. It is further held that the natrolite type channel s are emptied in further steps. Loss of water in steps even beyond 400 degrees C is particularly noted and such reactions are well reflected in the TG and the DTG. Peak temperature dependence on sample amounts is also evident. Successive phase transformations above 700 degrees C, up to 1000 degrees C are reflected in the DTA curves.