The single-phase nanocrystalline forsterite powder was successfully synthesized by mechanical activation of talc and magnesium carbonate powder mixture followed by annealing in the presence and absence of fluorine ion. Simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectrometry (AAS), and transmission electron microscopy (TEM) techniques were utilized to characterize the synthesized powders. The results showed that fluorine ion affected the mechanism of forsterite formation through producing some intermediate compounds. Chondrodite, humite, and clinohumite formed in the presence of fluorine ion during subsequent annealing as a transition compound and enhanced the forsterite formation rate. Fluorine ion was released from the system by hydrolysis in the form of HF. The single-phase nanocrystalline forsterite powder was successfully synthesized by 5 and 10 h of mechanical activation with subsequent annealing at 1000 degrees C for 1 h in the presence of fluorine ion. The obtained forsterite powder had crystallite sizes of about 53 and 47 nm, respectively, under each treatment. Their particle size was less than 150 nm. In the absence of fluorine ion, forsterite was fabricated with a crystallite size of about 36 nm by 10 h of mechanical activation with subsequent annealing at 1000 degrees C for 1 h. (C) 2010 Elsevier B.V. All rights reserved.