 Petrology of the Twin Sisters dunite consists of Enstatite rich rocks that contain, along with olivine, significant amounts of chromite, clinopyroxene, and serpentinite.These minerals are commonly associated with ultramafic rocks that crystallize below the Earth's crust within the mantle (geology).The serpentinized minerals are thought to have formed during later stages of the uplift where water could penetrate through fault fractures and initiate metamorphism.