The ammonothermal conversion of GaI3 to both cubic (zinc-blende) and hexagonal GaN was explored in detail. Gallium triiodide, anhydrous NH3, and in some cases CuI or LiI co-mineralizers, were sealed in quartz tubes and heated in a pressurized autoclave from 300degreesC to 515degreesC. At hot-zone temperatures above 430degreesC, a deposit of mostly c-GaN collects in the upper portion of the tube, and deposits of phase-pure c-GaN were reliably produced on a 50-60 mg scale when Cul co-mineralizer was added. Crystal morphologies of these microcrystalline c-GaN products are highly dependent on growth conditions and range from triangular prisms to triangular plates, dendritic crystals, and irregular particles. Hexagonal GaN products were either in the form of microrods or micron sized prisms. Nanorods, of presumably h-GaN, also formed in some reactions in low yields, intermixed with microcrystalline c-GaN products. (C) 2003 Elsevier Science B.V. All rights reserved.