Peridotite has undergone strong serpentinization and was completely replaced by serpentinite, but the pseudomorph of olivine and orthopyroxene still are preserved.
The Ophiolite massifs are composed of mantle peridotite that is mainly harzburgite and dunite, and lacked of crust magmatite within the typical Ophiolite suite.
We know that to a depth of about a hundred miles the mantle consists predominantly of a type of rock known as peridotite, but what fills the space beyond is uncertain.