Earlier optical table tops were sometimes made of a large slab of highly polished granite or diabase. These materials are very dense and stiff, which inhibits flexing and motion of the surface, improving the stability of the optical system. The surfaces can be ground extremely flat, which is beneficial for alignment of optical systems. Such tables were very heavy and expensive, however, and did not do a good job of damping vibrations. Mounting components to a granite surface is also difficult. Granite and diabase are still used for smaller precision-flat surfaces, but optical tables made from these materials are not commonly available today.