Rocks are grown off the coast of Japan. The rocks are soaked in ultraviolet rays for more than two hours.
They are called "rock postcards" and can be eaten in one bite. The rock postcards are sold at a cost of about $1.50 per piece. They can be found in Japan, the U.S. and Europe. They were made in Japan by a company based in Tokyo. The company is based in the town of Kansai, in the north of the country.