The decomposition of pure chrysotile from Thetford, Quebec heated at constant temperature in air from 200-1000°C for 4 to 720 hours was studied by using X-ray diffraction and optical microscopy techniques. No morphological changes were observed optically below 450ºC and 24 hours, although X-ray diffraction data suggest that chrysotile degrades then recrystallizes below 450˚C. Throughout the temperature range of 500-1000ºC, changes in the refractive indices observed included several cycles of increasing and decreasing magnitudes and ranges. Chrysotile was no longer present above 575˚C and 24 hours. The lowest temperature of forsterite appearance was at 500˚C and 720 hours and the lowest temperature of enstatite appearance was at 800˚C for 8 hours. Broad reflections were observed within 500-750˚C at 16-8Å, 4Å, and 3Å spacings. These reflections suggested the possible presence of talc and tridymite-like mineral phases. X-ray diffraction and optical microscopy results of this study show that the decomposition of chrysotile is more complex than previously understood.