In Westeros, there are only two substances capable of killing White Walkers: Valyrian steel and Dragonglass. The Maesters, however, refer to Dragonglass as obsidian -- a naturally occurring volcanic glass formed as an extrusive igneous rock.
In George R.R. Martin's books, as well as in real life, obsidian can be extremely dangerous. Well-crafted obsidian blades can have a cutting edge many times sharper than high-quality steel surgical scalpels.
Today, some surgeons use obsidian scalpel blades with the blade's cutting edge only 3 nanometers thick or almost 30,000 thinner than human hair. However, the history of obsidian blades goes much farther back in time.
The finest of these prismatic blades were produced in Mesoamerica about 2,500 years ago, according to Dr. Don Crabtree who re-discovered the production technique in the 1970s. "The prismatic glass blade is infinitely sharper than a honed steel edge, and these blades can be produced in a wide variety of shapes and sizes," wrote Bruce A. Buck in a paper published in 1982.
Motolinia, a 16th-century Spanish observer, left this account of prismatic blade production:
"It is in this manner: First they get out a knife stone (obsidian core) which is black like jet and 20 cm or slightly less in length, and they make it cylindrical and as thick as the calf of the leg, and they place the stone between the feet, and with a stick apply force to the edges of the stone, and at every push they give a little knife springs off with its edges like those of a razor." Hester et al. (1971)
The volcanic glass is thought to be so sharp because of the way it breaks, a pattern geologists call a conchoidal fracture. This means the obsidian breaks into pieces with curved surfaces that are razor thin and extremely sharp.
Over time, ancient peoples learned to break obsidian into tools of various shapes. All sorts of prehistoric artifacts made from obsidian have been found by archeologists, including knives, arrowheads, spear points, and scrapers.
[panel style="panel-success" title="What's Obsidian?" footer="Source: Geology.com"]
Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a "mineraloid." The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture
Black is the most common color of obsidian. However, it can also be brown, tan, or green. Rarely, obsidian can be blue, red, orange, or yellow. The colors are thought to be caused mainly by trace elements of inclusions. Source: Geology.com. [/panel]
Historians believe obsidian may have been the very first material actively mined and used to manufacture sharp tools at scale. Ancients may have transported these goods thousands of miles to trade for other goods and services.
Remarkably, obsidian tools may even predate humans! Researchers have found what they believe to be the oldest known stone-tipped throwing spears. The remains are so ancient that they actually predate the earliest known fossils of our species by 85,000 years. These spears were made from obsidian by either another species -- which had to be extremely crafty and clever -- or ancient humans. The latter possibility means that our species is at least 85,000 older than we believe.
The Pre-Incan civilization used brain surgery as an extensive practice as early as 2,000 B.C. with an inordinate success rate noted among patients, archaeologists say. These ancient doctors used brain surgery to treat a variety of diseases like mental illnesses, epilepsy, headaches, organic diseases, neuropathy treatment, osteomylitis, and head injuries. The surgical tools they used were made from bronze and shaped obsidian.
Despite the fact that obsidian is a very popular material used for mirrors, decorations, and even bogus energy trapping, the glass' main use nowadays is still as a cutting tool.