Izumo Stone

Mount Kasen was a land volcano that erupted andesite lava about 15 million years ago (middle Miocene). Silica deposited from water moving through cracks in the lava formed chalcedony veins in various colors, including green jasper (ao-menou) and red agate. Weathering turned the lava into soft red clay but left the chalcedony intact, so it is found in veins, in the clay, in river gravels and in terrace deposits; the best material comes from the western foot of the mountain. Mining continued until the late 1970s or early 1980s, and a preserved vein about 50–60 cm wide can be seen in an old mine tunnel.

Although called jasper, Izumo stone is mineralogically chalcedony, like agate. Matsue City notes that Izumo green jasper is deeper and more evenly green than the paler, less glossy Hokuriku jasper and green tuff used for beads earlier. Archaeologists also recognize Izumo-made beads by one-sided drilling: string holes were bored from one side only, a technique used for Kofun-period magatama and, from the late 5th century, for tubular beads; tubular beads drilled this way can almost always be attributed to Izumo agate-type stones.

Chalcedony from around Mount Kasen was used for stone tools as early as about 36,000 years ago. Green jasper began to be worked into tubular beads around the 1st century, and from the late 4th century Izumo beads were distributed across Japan; by the 6th–7th centuries Matsue was almost the only producer of stone beads in the country. More than 30 bead-workshop sites have been found around the mountain, and the Izumo Tamatsukuri Site, excavated in 1969 and 1971 with about 30 workshop remains, is a National Historic Site. Production resumed in the Nara and Heian periods, when beads were presented to the court, then ceased in the late Heian period. In the late Edo period a local craftsman, Itō Sen'emon, revived the work with techniques learned in Wakasa (Fukui), and Izumo agate craft is now a Shimane traditional craft.

Tamayu is traditionally said to be the birthplace of the Yasakani no Magatama, one of the Three Sacred Treasures of the imperial regalia. According to myth, Susanoo received a magatama from the deity of Tamatsukuriyu Shrine after slaying the serpent Yamata no Orochi and presented it to his sister Amaterasu. At the shrine a round "wishing stone" is enshrined beside a piece of raw ao-menou, where, by tradition, people prayed for success in making magatama. Today magatama of Izumo stone are popularly associated with good fortune and matchmaking (en-musubi).