Submicroscopical twinning in lunar and experimentally deformed pyroxenes

During deformation experiments at high pressures (10 kb) and medium temperatures (500–650°) diopside became twinned on {100} in small optically invisible domains. If host and twin occur with equal frequency, the X-ray single-crystal photograph would show orthorhombic symmetry due to the special geometry of the diopside lattice. A crystal of pyroxene from Mare Tranquillitatis has been found to give just such an X-ray photograph with orthorhombic symmetry; this is explained as a possible deformation product.