Boltwoodite has been synthesized at 185 degrees C (1.3 MPa) from quartz, KCl and uranyl nitrate by a new method avoiding local supersaturation of silicate species in solution. Sodium boltwoodite, uranophane, sklodowskite and kasolite were synthesized from boltwoodite. Unit-cell parameters and space groups were determined from the X-ray powder-diffraction data. Infrared spectra have intense absorption bands at 3458 and 3377 cm(-1), which correspond to OH-stretching vibrations. Bands at 1384 cm(-1) indicate the presence of SiO3OH groups in the structures. Luminescence spectra and solubility data are reported.