Rank of coal and metamorphic grade of rocks of the Narragansett Basin of Rhode Island

Abstract

The coal and the associated sedimentary rocks of the Narragansett basin are progressively metamorphosed from north to south and southwest. X-ray analysis seems to give more definite indication of rank of these high-ash high-rank coals than does chemical analysis.Both chemical analysis and X-ray analysis reveal a close correspondence between rank of coal and metamorphic grade of associated rocks. At Pawtucket, coal, judged on the basis of X-ray analysis to be anthracite, is associated with rocks of the muscovite-chlorite subfacies of the green-schist facies that contain muscovite, paragonite, and chlorite. At Ports-mouth, meta-anthracite is associated with rocks still in the muscovite-chlorite subfacies and containing muscovite, chlorite, and ilmenite. At the Cranston mine, higher-rank meta-anthracite is associated with rocks in the biotite-chlorite subfacies.