Neocene quartz. A type of soft volcanic tuff that is rough, porous and easily worked. It is a light, bluish greenish brown with blackish parts that vary in size from specks to pebbles. There are three layers: the topmost is called kaburi 被; the middle one is called shirome 白目; the bottom layer is the hardest stone of the three and is called aome 青目. The most commonly used ōya-ishi has large pockets or crevices, and is popularly called miso みそ. Because the quality is poor, the use of ōya-ishi is limited to slabs for veneers, gate walls, fences, foundations and gardens. It is soft, easy to process, rather cheap, fire resistent and waterproof. The best source of ōya-ishi now is in Ōyamachi 大谷町, Tochigi Prefecture from which the stone takes its name. Frank Lloyd Wright used it for the old Imperial Hotel in Tokyo.