A range of garnet structured compositions can be synthesized between the end members C3AH6 (hydrogarnet) and C3AS3 (grossularite) at different temperatures and pressures. The extent of this series at 95°C and a pressure of one bar has been investigated. The synthesis of a range of garnets from C3AH6 to C3AS1·5 H3 has heen attempted hy refluxing reactants at the same temperature and pressure. Product analyses were carried out using X-ray diffraction, electron microscopy, chemical and differential thermal/thermogravimetric analyses. Three target compositions from C3A H6 to C3AS0·24H5·52 gave one garnet phase plus C4AH13. Another three target compositions from C3S0·5H5 to C3AS0·76H4·48 gave two distinct Si-hydrogarnet phases: a low Si-hydrogarnet, approximately C3AS0·42H5·16, and a higher Si-hydrogarnet, approximately C3AS0·76H4·48. The remaining three target compositions, from C3ASH4 to C3AS1·5H3, again showed the two garnets to be present but with increasing amounts of calcium-silicate-hydrate gel (Ca/Si = 1·0) as the hulk Si content increased. It was found that the maximum Si content ohtained in Si-hydrogarnet was C3AS0·99H4·02. It is concluded that the 95°C, 1 bar range of garnet stahility is quite different from inferences drawn from studies made at higher temperatures and pressures.