The Rocks That Make Up the Keramas
This rock is black phyllite. Around 100 million years ago, mud that had built up on the floor of the warm sea hardened, and, through subterranean pressure, eventually became a rock stratum called phyllite. The thin layers, with their 30-degree tilt, testify to the Earth’s enormous power.
Most of the Kerama Islands are made of sandstone and greenschist. There are very few places in the Keramas where the Ryukyu limestone typical of Okinawa can be seen.
Roadside Rocks Indicate Kerama Origins
One place to see sandstone is the Chishi Observatory on Zamami Island. Greenschist can be seen in large quantities on Geruma Island, and examined from close up in the area near the Aka Ohashi Bridge. Ryukyu limestone, which originates from coral reefs, can be seen only in very small quantities just off Tokashiki Island. It is found at a depth of roughly 80 meters on the seabed around the islands.