Mercury in U.S. coal; abundance, distribution, and modes of occurrence

The U.S. Geological Survey (USGS) has compiled a nationwide coal information database over the last 25 years. A subset of the data, called COALQUAL, contains analyses of over 7,000 coal samples that have been collected or calculated to represent the entire thickness of a coal bed in the ground. The COALQUAL database is an extremely valuable source of information for raw or in-ground trace-element concentrations in U.S. coals and, if adjusted for the effect of coal cleaning in appropriate coals, can provide a first estimate of as-shipped mercury concentration in coal where data are not available.