Sending just 4 volts through a sand-and-seawater mixture for 28 days triggered mineralization. Using a rod-like electrode with a diameter of 2 centimeters could create a tube of rock up to 80 ...

The green sand is caused by ground up olivine ... There are also black-sand beaches, including one in Tenerife, caused by volcanic rock. A beach in the Canary Islands even has sand which looks ...