Coprecipitated xerogel precursors of nanocrystalline magnesium titanates, with a Mg:Ti stoichiometric ratio of 2:1, were subjected to thermal treatment in air at constant temperature, from 100 to 1300 degrees C, using a hot-stage X-ray powder diffractometer. The phase sequences, the kinetics of phase evolution and crystallite size were studied during the first hour of the process at different temperatures. Until 500 degrees C no diffraction peaks were observed. Between 550 and 800 degrees C the structure was a mixture of two cubic nanocrystalline coherent structures: qandilite-like and periclase-like forms. At 900 and 1000 degrees C, after 15minutes, geikielite and periclase appear in small amounts but the qandilite-like phase remains predominant; at 1100 degrees C and above, qandilite is formed again as a single phase. The diffraction lines were substantially broadened for all crystalline phases formed at low temperatures, becoming sharper with increasing temperature and time. The phase evolution is interpreted as a consequence of the decrease in the surface area to volume ratio with increasing temperature and time, thus decreasing the significance of the surface energy. Linear thermal expansion coefficients were derived for qandilite.