Coal, by its nature, is unstable and weathers when exposed to moisture and oxygen. Weathering can result in a general decline on the commercial value and technological properties of coal. Coals of similar chemical properties have been shown to combust differently, and the differences can be attributed to petrographic composition variations, poor combustion environments, and weathered particles. Stockpiled and dumped discard coals have been targeted for use by a lower power utility, and a novel technique was developed to quantify and qualify the degree of weathering in these coals. The petrographic based Abnormal Condition Analysis (previously referred to as the Weathering Index Analysis) considers features not typically characterized during routine petrographic analyses, but which may have an impact on the technological properties of coals. Discard coals ranging in age from 5 to 40 years where characterized to determine the extent of secondary weathering. Eight secondary weathering features, clearly different from inherent weathering, were qualified and quantified. Margin effect appears to be an early microscopic indicator of weathering, followed by discoloration. Alteration minerals have only been observed in stockpiled and dumped coals and hence could be a useful feature to benchmark when considering whether or not a coal has been stored. Long-term stored coals have microcrack and fissure patterns clearly different from fresh coals. The length of exposure to weathering processes was determined to be proportional to the extent of weathering as determined petrographically. The Abnormal Condition Analysis should be used as a supplement to routine coal petrography as it can assist with the determination of anomalous behavior of coals. (c) 2007 Elsevier B.V. All rights reserved.