Obsidian is a volcanic rock formed when lava cools quickly. Depending on the other minerals involved, a variety of colors and even patterns can form in the obsidian. The material is considered a glass and was shaped into knives, spear or arrow points by prehistoric peoples. The art of "knapping," often done with flint, can also be done with obsidian to produce these items. The material can also be cut using modern lapidary tools.
Diamond Lapidary Saw
Lapidary saws use a diamond coated blade in a water or oil bath. The liquid removes the grit created by the blade cutting through the obsidian and keep the blade from overheating. The saws are available in a number of sizes depending on the size of mineral specimens you plan to cut. This type of saw and blade are the standard stone cutting tool for lapidary projects.
Knapping involves flaking away portions of the obsidian to form the shape of an arrowhead, spearhead or knife. Tools used include antler or stone to break away small pieces along the edge. Because obsidian is a glass type material, the broken edges become sharp. While knapping is not a cutting process it is used to shape the obsidian.
Obsidian can also be shaped for cabochons or other jewelry pieces using grinding wheels. These grinding wheels use an abrasive to remove excess material to form the desired shape. The obsidian stone is cut into a flat slab shape using the diamond lapidary saw and the ground to the desired shape. Wheels with finer abrasives are used to polish the stone.
Obsidian is volcanic glass and can break or shatter if handled aggressively while being cut or shaped. Wear safety glasses and leather gloves while working with obsidian. Clean up the work area carefully avoiding touching the cut edges and treat the grit and debris created while working with obsidian the same way you would shattered glass.