Applied Clay Science, 4 (1989) 509-519 509 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Expansibility of Some Vermiculites A. JUSTO 1, C. MAQUEDA2, J.L. PEREZ-RODRIGUEZ1 and E. MORILLO 2 iInstituto de Ciencia de Materiales, C.S.I.C., Apartado 1052, 41080-SeviUa (Spain) 2Instituto de Recursos Naturales y Agrobiologia de Sevilla, C.S.I.C., Apartado 1052, 41080 SeviUa (Spain) (Received February 10, 1988; accepted after revision January 13, 1989) ABSTRACT Justo, A., Maqueda, C., Perez-Rodrlguez, J.L. and Morillo, E., 1989. Expansibility of some ver- miculites. Appl. Clay Sci., 4: 509-519. The thermal expansion of four samples of "vermiculite", one sample containing both vermicu- lite and mica and one sample containing vermiculite and mica/vermiculite interstratification from various geological origins have been studied. All samples yield good pyro-expanded products. How- ever, minerals containing mica or mica/vermiculite interstratification have the highest expansi- bilities. It is suggested that the sudden release of interlayer water is not the only factor influencing the thermal expansion of these samples, e.g. the presence of relicts of altered mica, loss of OH groups or chemical composition. INTRODUCTION The term "vermiculite" used in the industry comprises not only the mineral vermiculite, but also materials containing mica/vermiculite interstratifica- tions, mixtures of mica and vermiculite, etc. The principal characteristic on which most of the industrial uses of vermiculite is based is its property of ex- foliation when the mineral is suddenly heated to a high temperature. So low- density materials are obtained, used for many different applications, such as thermal and sound insulation, semi-refractories, fire protection, light-weight aggregates for concrete, agriculture and horticulture, etc. (Kimpflin, 1954; Cowling and White, 1954). This property of exfoliation is explained as due to the explosive release of water molecules from between the silicate layers, and causes the flakes to ex- pand to twenty or thirty times their original size normal to the basal cleavage. Midgley and Midgley (1960) and Couderc and Douillet (1973) found that the greater expansion is achieved in the case of regular mica/vermiculite inter- stratification. The latter authors ascribed this to the fact that during thermal shock, the water molecules from the vermiculite layers hit the mica layers, 0169-1317/89/$03.50 © 1989 Elsevier Science Publishers B.V.