weathered coal

n
coal that has been exposed to climatic conditions (precipitation, sunlight, wind, temperature variations, etc.) and sometimes ground water, such that its properties are altered compared to those in coal from the same seam that has not be so exposed.
DISCUSSION — Weathering is always accompanied by oxidation of the organic material, commonly resulting in an increased concentration of oxygenated functional groups (for example OH and COOH). More pronounced weathering is accompanied by cracking and frequently, by mineral efflorescence. Milder weathering may not be detectable by visual inspection, but all weathering is manifest by increased solubility in alkalis (see Test Method D5263), reduced calorific value, and, for bituminous coals reduced agglutinating or agglomerating properties upon heating. D388, D720, D5515

ASTM D121-09a Standard Terminology of Coal and Coke. 2014.

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