The Nomenclature of the Banded Constituents of Coal

Abstract

IN view of the wide acceptance in Great Britain of the terms vitrain, clarain, durain, and fusain devised by Dr. Stopes to describe the banded constituents of British bituminous coal, and the introduction of the further terms anthraxylon and attritus by Dr. R. Thiessen, it may be of interest to define the relation between them. At a recent symposium of the Coal Research Club, at which both Dr. Stopes and Dr. Thiessen were present, it appeared to be agreed that the two systems have entirely different bases and that each has its validity and use. It was the important service of Dr. Stopes (Proc. Roy. Soc., 1919) to replace the vague terms bright and dull coal by others capable of exact definition. The basis of her system is a lithological one. There are two kinds of bright coal. Vitrain is not in itself banded, and has a glassy lustre and conchoidal fracture. Clarain is inherently banded or striated, and consequently scatters light, and has a silky lustre, and does not break with a conchoidal fracture. These purely lithological characters are sufficient to define the terms, without resort to the microscope, a feature essential for practical purposes to retain. Dr. Stopes correlated them with the microscopic and chemical characters, but these are under further investigation.