B. W. Chappell is an authority in the geochemistry and origin of granitic rocks. His sustained study of granites from SE Australia and their lithic inclusions led him to recognize that many granite magmas move bodily away from their sources deep in the crust as a mixture of melt and solid residual material , which implies that many granites exposed at the surface reflect the nature of their deeper source materials. He was a pioneer in using X-ray spectrometry for trace element analysis which has led to his making contributions in several other fields, most notably in the analysis of lunar samples.