ÅŒya Stone
Ōya Stone (Jap.大谷 石, Ōya - ishi ) is a bright Tuff stone that is found in the vicinity of the place Ōya, now part of Utsunomiya, and is used from time immemorial for house building.
Description
The rock was formed in early Tertiary, when the Japanese islands were still largely under water, by solidification of ash from volcanic outbreaks in the water. This rock is found exclusively in the vicinity of the hamlet Ōya in an area of 8 km east-west and 37 km north-south and at a depth of 200 to 300 m.
Because of its lightness properties, fire resistance, easier processing of stone for homes, storage, fireproof walls, moat - fixing, as floor tiles, stone walls, gate posts, building cladding was, inter alia, uses. Especially in Utsunomiya is frequently to see the stone in total, one third of the production in the Kantō region.
Due to the increasing use of concrete, the demand - in spite of the good availability and good appearance - decreased. Occasionally, however, is also observed susceptibility to weathering.
Reduction
In order not to disturb the agriculture, the stone is mined underground, with large caves occur, some of which were expanded in 1944 to storerooms of the army. 1979, a cave was open as a museum to the public. 1989 crashed at another point a an ancient cave, creating a crater 100 m in diameter and 30 m deep was formed. Then the area was searched for abandoned and uncharted caves.
Originally the stone was mined by hand. Here, a "crane - beak" ( Tsuruhashi ) mentioned simple tool were blocks of size 5 × sun × 3 1 shaku shaku removed. A worker in this way succeeded ten blocks day, wherein there was also troublesome to bring the blocks 70 kg to the surface. - How was still proceed until about 1960, but already in 1952 began with the mechanical degradation. This allowed the yield to 50 blocks per worker per day to be increased.