the ham diatreme and dyke are post-late silurian intrusions located in north-central somerset island and are the most northerly known kimberlites in the somerset island kimberlite province. the ham diatreme, which consists of three petrographically distinct varieties of kimberlite, formed as a series of fluidized intrusions at the intersection of several regional fracture sets. type la kimberlite is petrographically similar to the ham dyke (a single intrusion located 1.5 km to the east) and forms the flanks of the ham diatreme. this dark, massive rock contains phenocrysts and xenocrysts of garnet, olivine, chrome-diopside, phlogopite, spinel and carbonate in a serpentine-carbonate groundmass containing carbonate and serpentine emulsion textures. type ib kimberlite, which occupies the central portion of the ham diatreme, is a highly altered, light green, serpentine-carbonate-rich rock formed by the prograde serpentinization and carbonatization of type la kimberlite. this alteration occurred during the degassing of structurally lower portions of the ham diatreme. type 2 kimberlite is a carbonate-rich mineralogical equivalent of type la kimberlite and formed as a late stage dyke within the ham. diatreme.