Amphiboles are also specifically less dense than the corresponding pyroxenes. It is typically associated with pyroxenes and olivine. Basalt is composed of minerals readily available in the planet's crust, including feldspars and pyroxenes. Hypersthene is a common rock-forming inosilicate mineral belonging to the group of orthorhombic pyroxenes. Feldspar, amphiboles, pyroxenes, and volcanic glass are the principle donors of clay minerals. Boninite typically consists of phenocrysts of pyroxenes and olivine in a crystallite-rich glassy matrix. In chemical composition and general characteristics they are similar to the pyroxenes. The principal pyroxenes in gabbro are clinopyroxenes, generally medially iron-rich augites. Calcium-rich pyroxenes and olivine, along with nickel-iron metal, have been detected on Eunomia's surface. Parts of the southern highlands include detectable amounts of high-calcium pyroxenes. With high alkalis, soda-bearing pyroxenes and amphiboles may be present. Amphiboles and pyroxenes are common accessory minerals. Biotite, amphiboles and pyroxenes are common dark accessory minerals. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates (whitlockite, stanfieldite, farringtonite, and merrillite). Common mineral associates in igneous rocks include olivine, pyroxenes, amphiboles and magnetite.