Iron ores in the Gushan deposit, Anhui Province, occur in a contact tone between Mesozoic gabbro diorite and its country rocks dominated by Triassic shale, siltstone and sandstone. They are composed principally of hematite microcrystallites, mostly 0. 01 - 0. 05 mm in size, inter-grown with chalcedony and fine-grained quartz. Hematite phenocrysts, up to 1 - 2 mm in size, can be seen to occur as euhedral laths disseminated in massive ores.Microscopic observations have revealed that euhedral phenocrysts of hematite were formed by post-mineralization coalescence of hematite microcrystallites. It is suggested that the whole process involves mutual approaching, grain rotation, crystallographical orientation and eventual welding of the microcrystallites. The resultant porphyroblasts show optical uniformity. A series of microphotographs are given to illustrate each stage of the process.