Itoigawa Jade

Itoigawa and its surroundings (Asahi, Otari and Hakuba) are Japan's largest jade source. Jade boulders are exposed in the Kotaki River and Omi River jade gorges, both designated and protected as natural monuments, and with luck visitors can still find jade among the pebbles on Itoigawa's gravel beaches. Jade, which forms only in subduction zones like Japan's, is also found at other Japanese localities such as Wakasa in Tottori, Oya in Hyogo, Osa in Okayama and Nagasaki, but gem-quality jade is abundant only at Itoigawa.

Unlike single-crystal gems, jade is an aggregate of minerals. The Fossa Magna Museum uses the name jade (hisui) for rock made mostly of jadeite or omphacite, and calls dense rock made mostly of tremolite–actinolite nephrite; in the West the two are still confused and even serpentinite is sometimes labelled jade. A stone formerly sold in Itoigawa as "pink jade" is not jade but rodingite containing pink clinozoisite (thulite).

People in Itoigawa began working jade in the Jomon period, about 5,000–5,500 years ago, making large beads (taishu) and magatama that were traded across Japan; local sources call this the world's oldest jade culture. Jade remained treasured through the Yayoi and Kofun periods but fell out of use from the Nara period, and its Japanese source was forgotten. Itō Eizō found green stones in the Kotaki River area in the 1930s (traditionally dated 1938, though the Fossa Magna Museum considers 1935 likely), and in 1939 Kawano Yoshinori of Tohoku University confirmed them as jade. In 2016 the Japanese Association of Mineralogical Sciences selected jade as Japan's national stone.

According to local tradition, Princess Nunakawa, who once ruled the Itoigawa region, wore a jade magatama; this story prompted the writer Sōma Gyofū to suggest that jade might be found locally, which led to its rediscovery.