Oshima granite

Oshima stone comes from Oshima in Imabari, Ehime, with its main distribution centered on the northern part of the island. Quarry areas are found in Miyakubo and Yoshiumi, with a concentration on the eastern slope of Nenbutsuyama; the Stone Culture Heritage Hall stands at 3546 Miyakubo, Miyakubo-cho, Imabari, giving the stone town a concrete public doorway.

The local identity here is visible in place and work: northern Oshima quarry land, a stone-filled hall in Miyakubo, stone businesses in Yoshiumi, and a stone-processing cooperative in Imabari. Walls, outdoor carvings, and polished surfaces around Miyakubo all point back to the same island rock body and the communities that cut, move, shape, and maintain it.

Oshima stone is more precisely described as granodiorite. Compared with standard granite, it is richer in dark minerals and plagioclase; it is gray-black, fine to medium grained, dense, and hard. When polished, the surface shows a bluish cast linked to plagioclase, a feature behind the older name ao-mikage, or blue granite-like stone.

That color is tied to use as well as appearance. Oshima stone is described as resistant to weathering, able to keep its gloss, and unlikely to discolor; the Stone Culture Heritage Hall also presents it as a stone that gains character with polishing. On a gravestone face, a building edge, or an outdoor monument, the blue tone is the visible result of mineral composition, polishing, and long exposure to the elements.

Local memory connects Oshima stone with the construction of Imabari Castle, placing the stone within Imabari and Oshima's remembered stonework. From the Meiji era onward, transport roads, ports, and wider sales routes helped Oshima stone move into larger works beyond the island.

Named uses show the breadth of that movement. Regional accounts list foundation stones for the Imperial Palace reconstruction, work connected with the Kure naval port, Osaka Shinsaibashi, Dogo Onsen, the first annex of the Ehime Prefectural Government, the prefectural assembly building, and the prefectural culture hall; the Stone Culture Heritage Hall also names the National Diet Building and Osaka Shinsaibashi. Castle memory, harbor works, bridges, and public buildings give Oshima stone a history measured in weight, surface, and place.

Oshima stone was once used broadly for bridges, stone walls, coastal works, and building stone. After the war, as the cement industry grew, its uses narrowed, and production came to center on gravestone material. A 1983 product-weight account says cut stone for cemetery-related goods made up most of the output at about 28,500 tons; a 1981 breakdown also placed fine-grained stone for cemetery-related use in the high-grade category.

The connection with gravestones rests on specific material traits: fine grain, hardness, weathering resistance, gloss retention, and resistance to discoloration. The Imabari-city Stone Processing Cooperative was established in 1979 and lists eight member companies, with work tied to cemetery stone construction, repair, relocation, removal, and related stone processing. Through those workshops and businesses, Oshima stone moves from quarry blocks into shaped stone and long-term care.

Earlier quarry work depended on chisels, hammers, mine carts, horse-drawn transport, and stone boats. In the Showa period, rock drills, jet burners, backhoes, cable cranes, trucks, ferries, and direct transport routes changed how blocks were cut from the rock, moved down from the quarry, and sent out from the island.

Mechanization made the scale of the work easier to grasp. A fresh block had to be split from a rock body with few cracks, moved, cut, processed, and finished as gravestone material, building stone, or sculpture material. In Yoshiumi, Seizan handles Oshima stone from quarrying through processing, sales, and installation, showing how one local stone business can span the mountainside, the workshop, and the final site.

At the Stone Culture Heritage Hall in Miyakubo, Oshima stone appears beside stones from around the world, and outdoor sculptures and simple monuments invite close viewing and touch. The hall also presents stone history and culture; here, culture means the building's stone surfaces, outdoor works, displays, and Miyakubo's quarry memory.

In Yoshiumi, Seizan opens its headquarters as the Ishi Konjaku Gallery, displaying stone objects and ornaments and serving as a social-learning site for local elementary and junior high school students. Stone-splitting and stonework experiences bring Oshima stone back to hands, tools, chips, and surfaces, keeping the work of Miyakubo and Yoshiumi visible beyond finished gravestones and buildings.