Classification of coals according to degree of coalification by reflectance of the vitrinite component

The utility of reflectance of the vitrinite component of coals as a criterion of degree of coalification has been investigated. Present standard systems for classification of coals by rank are intended mainly as guides for utilization behaviour, and there is a need for more widespread acceptance and usage of an objective rank criterion based more firmly on physical/chemical characteristics of a coal. The relations of reflectance of vitrinite to other commonly used or proposed rank parameters have been studied, using voluminous data supplied by United States and European laboratories. These relations were found to be excellent for high-rank bituminous coals, good for anthracitic coals, fair for low-rank bituminous coals, and rather poor for subbituminous coals, lignites, and brown coals. The data for the last category are least numerous, and work is continuing on their reflectance—rank characteristics, especially for the International Commission on Coal Petrology. The reflectance ranges established for present rank categories are listed and it is proposed that they be included in standard classification systems as supplementary criteria of rank.