In Tasmania, peridotite inclusions occur in abundance in Cainozoic volcanic rocks ranging in type from olivine tholeite, alkali olivine basalt, limburgite and basanite to hawaiite, benmoreite, mugearite, and nephelinite. The inclusions are commonly of spinel lherzolite, and are considered to be accidentally derived from the upper mantle. Some of the inclusions display textural and compositional evidence of sub-solidus reactions that involved the production of spinel and pyroxenes from more aluminous pyroxenes. These reactions are likely to have proceeded as a consequence of falling temperature at high pressure. Inclusion textures appear to be related to their crystallization temperatures. The compositional variations in the coexisting minerals of the Tasmanian inclusions are interrelated, and fall into two groups, one perhaps arising from variations in bulk composition, and the other from sub-solidus equilibration over a considerable PT range. They do not result directly from processes of crystal-liquid equilibria.