Handling Editor: M. SantoshThe Silurian Diana Mills pluton is a metamorphosed mafic-ultramafic body in the Piedmont Province of Virginia. Major rock types in the pluton include metadiorite and chlorite-amphibole rock, with lesser amounts of hornblendite. However, the most visually striking rocks, found at 4 locations, consist of tan-weathering nodules in a dark green matrix. The purpose of this study was to investigate the origin of these nodular rocks. All rocks show evidence of greenschistfacies metamorphism, but relict igneous textures are preserved locally. Apart from the nodules, Ca-amphibole is ubiquitous in all rock types. Nodules are dominated by serpentine or talc (+magnetite ± chromite), and many show a thin (≤5 mm) radially oriented shell of serpentine against adjacent matrix. The nodules are ultramafic (Mg#~80-90, up to7,563 ppm Cr, up to 2,038 ppm Ni), and their normative mineralogy is dominated by olivine and orthopyroxene. Thus, they represent metamorphosed harzburgites and pyroxenites. Matrix minerals are dominantly amphibole + chlorite, along with variable amounts of talc + magnetite. Some matrix samples are chlorite-rich, probably reflecting metasomatic reaction with nodules (i.e., they are small-scale "blackwalls").Matrix samples are also ultramafic (high Mg#, Cr, and Ni). The matrix of the nodule-bearing outcrops is essentially the same as other chlorite-amphibole rocks elsewhere in the pluton. We consider these rocks to represent emplacement of an original hornblende peridotite crystal mush (a mixture of crystals and hydrous melt), which locally carried harzburgitic nodules. The nodules most likely represent the earliest-formed cumulates from the Diana Mills parent magma.