We have investigated devitrification of glasses within infrared transmitting xSbSI-(100-x)Sb2S3 pseudo-binary series, which forms SbSI and Sb2S3 ferroelectric crystal phases. Differential scanning calorimetry (DSC) and X-ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one-dimensional crystallization at low temperature which starts from the sample surface, and three-dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high-temperature exothermal peak to the low-temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb2S3 phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms.