A study of the hydrothermal reactions of metakaolinite in alkaline solution has been made. Metakaolinite has proved to be a versatile starting material for alumino-silicate preparation, particularly zeolites. Approximately thirty zeolites crystallized from the compositions studied. This included the first preparation of the Rb analogue of phillipsite, and a siliceous form of the chabazite-like K-G which had a very high sorption capacity. Highly alkaline solutions have permitted the temperatures required to produce both hydrated and non-hydrated products to be lowered considerably, for example zeolite K-F, analcime and kaliophilite. Syntheses from magmas containing two bases produced cancrinite at a temperature as low as 80°, and also new cationic variations of existing zeolite frameworks such as Na, Li-F. The chemical, sorptive and crystallographic properties of many of the crystalline products have been investigated. Zeolite Ba-G has been re-indexed and identified as having the zeolite L framework. A new synthesis from the K,Ba system 3 has produced a zeolite which is the aluminous end member of the zeolite L family. This has the 7.5 Å channel system available for sorption and although aluminous it has a very high thermal stability. A re-examination of zeolite Linde N has led to its confirmation as a single species and a new unit cell. The rubidium analogue of K-F has been indexed on a tetragonal unit cell and the relationship to the other members of the K-F family discussed. The mechanism of zeolite crystallization has been followed by measurement of the rate of formation of the zeolites and of the change in composition of the solutions. This is discussed with respect to other systems, for example kaolinite and aluminosilicate gel syntheses. Where possible, syntheses and products have been compared to natural processes and natural zeolites.