ABSTRACT: Volcanic activities ^create rhyolite and rfayodacite type of acidic volcanites together with, economic gradeof perlite deposit in. the west part of Anatolia.Thennogravimetric analyses on selected perlite samples from the deposits reveal that the volatile content in the perlitesare between %2,5-5„ There are three equilibrium, stages of loss volatiles in perlitle rocks as 120 C 4.50 C° and 950 CInfrared spectrophotometer analyses indicate that, the big` amount of`the water- in perlites in present as. moleculer H2Oand rest. in. `the from of Si-OH groups. The water molecules are trapped in the crystal lattice either by weak hydrogenbonds to the anion or by weak ionic bonds to* the metal. The weak, bonded, water molecules, release `the rock at 450 C°.The small amount of remaining volatiles account for expansion, characteristic of the rock.