Tatami-ishi (畳石, Tatami-ishi), literally "tatami stones", is a geological feature in Kumejima, Okinawa, Japan. Located on the south coast of the island of Ōjima (奥武島), to the immediate southeast of Kume Island, it lies within Kumejima Prefectural Natural Park. Exposed at low tide, the feature comprises some one thousand pentagonal and hexagonal rocks, each 1 to 1.5 metres in diameter, stretching fifty metres from north to south over a length of two hundred and fifty metres. It was formed during the Miocene period by the columnar jointing of andesitic lava as it cooled and contracted. The name is derived from the resemblance to a room of close-fitted tatami mats, while the feature is sometimes also likened to a turtle's carapace.[1][2][3][4][5] In 1967 Tatami-ishi was designated a Natural Monument by the Government of the Ryukyu Islands. With the reversion of Okinawa to Japan in 1972, it was redesignated a Prefectural Cultural Property. In 2014 an area of 29.3 ha was designated a national Natural Monument.[2][6]
^ ab「久米島町奥武島の畳石」国指定へ [Tatami-ishi on Ojima, Kumejima designated a National Natural Monument] (in Japanese). Kumejima Town. Retrieved 30 September 2016.
^Nakagawa Hisao; Murakami Michio (1975). "CiNii Research" 沖繩群島久米島の地質 [Geology of Kumejima, Okinawa Gunto, Ryukyu Islands, Japan] (PDF). Contributions from the Institute of Geology and Paleontology, Tohoku University (in Japanese and English) (75). Tohoku University: 1–16. Retrieved 30 September 2016.
