The Faile growth method, when used with purified mercuric iodide (HgI2), along with low molecular weight polyethylene, has yielded tetragonal prismatic HgI2 crystals. Thermal desorption-gas chromatography/mass spectroscopy (TD-GC/MS) studies reveal the existence of alkanes and ketones in the growth ampoules along with low molecular weight polyethylene, presumably decomposition byproducts from, or impurities in, the polyethylene. The influence of these desorbed byproducts on the HgI2 crystal morphology is compared to the basic Bravais-Friedel-Donnay-Harker (BFDH) crystal model. From these comparisons, it is apparent that ketones assert the most influence on the HgI2 crystal morphology by slowing the growth of the {110} faces, thereby, causing the tetragonal prismatic crystal shapes to grow. (c) 2013 Elsevier B.V. All rights reserved.