This paper examines an Australian garnieritic-type ore and changes in phase composition and morphology caused by heating in argon at 400-1000 °C using XRF, XRD, DTA/TG, SEM/EDS and BET analyses. The mineral phases detected by XRD in the original ore include chlorite, talc, hematite and quartz. Traces of iron silicate, Fe-Cr spinel and monoxide phase (predominantly manganese oxide) were observed by EDS. Nickel was detected in chlorite, talc, iron silicate and monoxide phase. Heat treatment at 400-500 °C did not change XRD patterns. At 600 °C, dehydroxylation of the brucitic phase of chlorite occurred. Chlorite was converted into olivine (forsterite) and enstatite at 600-800 °C. Upon heating to 900-1000 °C, talc was also converted into olivine and enstatite. Ni-bearing phases after heat treatment at 800-850 °C were forsterite, enstatite, talc, iron silicate and monoxide.