We have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically-prepared, semi-crystalline phase with Ca:Si = 1, we have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250°C. Analysis in each case was by x-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM) and x-ray diffraction (XRD). There was increased silicate polymerisation with both increased synthesis temperature and duration of synthesis. Concerning crystal morphology, there was an increase in crystal size with increasing temperature, but this led to some crystal damage. Longer hydrothermal treatment however led to more perfect crystal morphologies.