Using a new analytical transmission electron microscopic technique known as Channeling Enhanced X-ray Emission (CHEXE) spectroscopy, the M-site occupancies of Fe, Ni, Mn, and CA have been determined in a natural forsteritic olivine (Fo91) heat treated at different temperature. The sample was taken as a single olivine grain from a spinel periodite inculsion in an alkali basalt and contains 0.36 wt% NiO, 0.07 wt% MnO, and 0.09 wt% CaO. In the non-heat-treated sample, 49.6 at% of the Fe, 97¿5 at% of the Ni, and 2¿5 at% of the Mn in the sample occupy the M1 site. In the present study of samples quenched from different temperatures, the fraction of the Ni present at M1 is 87¿5% (6 days at 300 ¿C), 83¿5% (48h at 600 ¿C), 83¿5% (45 h at 900 ¿C) and 80¿5% (24 h at 1050 ¿C). We thus observe a lesser tendency for Ni to order than postulated by previous for Ni-rich olivines. For Mn, typically 15% of the atoms occupy M1 in the heat treated samples. No significant deviation from complete ordering into M2 was observed for Ca. The Fe atoms are completely disordered with 50¿1% at each M-site, except for a weak deviation at 300 ¿C with 47.1¿1% at M1. The study indicates that exchange of cations between M-sites may begin as low as 300 ¿C. This implies that Ni and Mn distributions in natural olivines may be a useful indicator of cooling rate in rapidly cooled rocks.