Abstract: A novel family of substantially amorphous aluminosilicate catalysts and a process for the manufacture thereof are described. In the process, a source of silica, a source of alumina and a source of an alkali metal are mixed in an aqueous medium and then subjected to hydrothermal treatment at a temperature of from 20.degree. C. to 200.degree. C. for a period of from 1 hour to 250 hours, the reaction conditions and duration being selected so as to produce a solid which is substantially amorphous. The invention also extends to the use of the calalyst in acid catalyzed reactions such as the skeletal isomerization of normal olefins, in particular normal butene, and to the use of the catalyst as a support in metal catalyzed reactions.