Oya stone

Japanese: 大谷石 - おおやいし

This stone is made of rhyolitic pumice tuff found in Oya, Utsunomiya, Tochigi Prefecture, and is a typical Japanese soft stone for construction. It is a volcanic product from the Miocene epoch of the Neogene period (approximately 23.03 million to 5.33 million years ago), and is a type of green tuff. The original rock-forming minerals, feldspar, have been altered into kaolin and sericite, and the colored minerals have been altered into epidote, chlorite, serpentine, titanite, and other minerals. As a result, the stone has a pale gray-green or pale yellow-green appearance, with dark brown or greenish-brown areas scattered in a mottled pattern. These brown areas are soft and are called "miso." Stones containing a large number of large miso particles are considered unsuitable for use as stone. There are various types of stone, including the blue-green "Aome" which is mined deeper underground, the whitish "Shirome" which is mined near the surface and is harder and of higher quality than Aome, and the finer-grained "Tora-me". Generally, it is porous, absorbs water easily and is vulnerable to freezing, but is resistant to fire and heat and is stable even at temperatures above 1000°C. It is softer than other stone materials and is easy to mine and process. It is quarried as cut stone in open-cut mines and tunnel digging, and is widely used for civil engineering and construction. It is used for fire-resistant purposes in warehouses and stone storehouses, as well as for foundations and stone walls. American architect F. L. Wright used it in the construction of the former Imperial Hotel.

[Saito Yasuji]

Oya Stone
A type of green tuff. Produced in Otani, Utsunomiya, Tochigi Prefecture. ©Shogakukan ">

Oya Stone

Stone storehouse
This stone storehouse remains in the Ena district of Iwaki City, which once prospered as a fishing town. It was built in the Taisho era. The exterior of the wooden frame is made of highly hygroscopic Oya stone, and it was used to store ship equipment and fishing gear. During World War II, the exterior walls were painted black with charcoal out of fear that it would become a target in air raids. Remnants of this can be seen here and there. Iwaki City, Fukushima Prefecture ©Seishohmaru ">

Stone storehouse

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

栃木県宇都宮市大谷に産する流紋岩質軽石凝灰岩の石材で、日本の代表的な建築用軟石。新第三紀中新世（約2303万～533万年前）の火山噴出物で、いわゆる緑色凝灰岩（グリーンタフ）の一種。もとの造岩鉱物の長石はカオリンや絹雲母(きぬうんも)に、有色鉱物は緑簾石(りょくれんせき)、緑泥石、蛇紋石、チタン石などに変質している。そのため外観は淡い灰緑色ないし淡黄緑色を呈し、中に暗褐色または緑褐色の部分が斑(まだら)状に散在している。この褐色部分は軟らかく、「みそ」とよばれている。大きなみそが多数含まれているものは、石材に不適とされる。より深い地下でとれる青緑色の「青目」、地表近くでとれ、青目より硬く良質で白っぽい「白目」、より細粒の「虎目(とらめ)」などの種類がある。一般に多孔質で、水分を吸収しやすく凍結に弱いが、火熱に強く、1000℃以上でも安定である。ほかの石材に比べて軟らかく、採掘や加工が容易である。露天掘り、坑道掘りで切り石として採石され、土木・建築用に広く利用されている。耐火用として倉庫や石蔵に用いられるほか、土台や石塀にも用いられる。アメリカの建築家F・L・ライトは、旧帝国ホテルの建築に用いた。

［斎藤靖二］