There are three petrogenetically different pyroxenites, namely cumulate pyroxenite, metamorphosed oceanic crust, and metasomatic pyroxenite. To explain the co-existence of pyroxenites of different origins within a single ultramafic massif, the following model is conceived: the oceanic upper crust, including basalts and sediments, produces considerable elementally variable fluids and magmas, which react with surrounding peridotites and convert it to pyroxenites and also form type I pyroxenites by high-pressure crystal segregation along magma conduits in the peridotites.