Greenstone

Greenstone, a rock term (now disused) for any dark green basic crystalline 'trap-rock.' The greenish tint which such igneous rocks so frequently show is now recognised as being in most cases due to the presence of serpentine, chlorite, or other products of decomposition. Most greenstones are thus referable to the Basalts (q.v.) and the Diorites (see IGNEOUS ROCKS).