This paper describes the low temperature hydrothermal synthesis of y-Y₂Si₂O₇ from a layered silicate (2 ∶ 1 clay), a precursor which acts as a structure-templating agent. Both the transformations undergone by the clay during the hydrothermal process and the new products formed at different reaction stages have been characterised at both long and short range orders. Secondly, the influence of the aluminium content of the clay on the stability of y-Y₂Si₂O₇ has been investigated. For this purpose, another layered clay, containing nominally no Al, has been submitted to the same hydrothermal treatment as the previous one. The results indicate that the amount of aluminium present in the starting material assists the stabilisation of y-Y₂Si₂O₇. The behaviour of y-Y₂Si₂O₇ with increasing temperature has been studied and the sequence of polymorphs and transition temperatures are reported and compared with those found in the literature.