The deterioration of some volcanic rock from Egypt was investigated using x-ray diffraction, atomic absorption, thin section analyses, and scanning electron microscopy. In the present work, the mechanisms of deterioration due to the role of water, change in temperature, and ultraviolet radiation exposure are discussed. A comparative study of basic and acidic volcanic rock is presented including the degree of crystallinity as a parameter in the deterioration process. Water-repellent silicon resin materials are very useful in the conservation of volcanic rock.