In the quarries, the stones were cut out from the wall deposits of calcite as rough upright disks. It seems that they were then propped up against natural or artificial walls for shaping, finishing and polishing. The rough work appears to have been done with pickaxes or adzes, with blades 1 to 3 cm wide, made of stone or of the shell of large clams such as "Tridacna". According to oral traditions, the central hole was made with a coral reef stone used as a "fire drill", presumably a large bow drill. (While the clam shells and coral are made of calcium carbonate too, they consist of the aragonite form, which is harder than the stone's calcite (3.5–4.0 and 3.0 in the Mohs hardness scale, respectively).