Growing up in a village in Kagawa Prefecture on the island of Shikoku, Masashi Tomikawa never thought twice about the geology of his surroundings. The volcanic rocks that surrounded him, however, are now part of the drummer's arsenal of sound.

"In my village the rocks have been used since ancient times," Tomikawa says. "But people outside of Shikoku have often never heard of them."

The black sanukite stones, known locally as kankanishi (cling-clang rocks), have been used to make tools for more than 10,000 years. When Tomikawa was a young boy, he recalls teachers taking elementary and junior high school students up the slopes of Mount Kanayama in Kagawa Prefecture to collect the rocks — just as his grandmother was forced to do during the war, when the stones were used as part of the protective armor for military aircraft.