It is sometimes classified as a mineraloid. Obsidian is mineral-like, but not a true mineral because, as a glass, it is not crystalline in addition, its composition is too variable to be classified as a mineral. Tektites were once thought by many to be obsidian produced by lunar volcanic eruptions, though few scientists now adhere to this hypothesis. Intrusive formation of obsidian may occur when felsic lava cools along the edges of a dike. Extrusive formation of obsidian may occur when felsic lava cools rapidly at the edges of a felsic lava flow or volcanic dome, or when lava cools during sudden contact with water or air. Obsidian is formed from quickly cooled lava, which is the parent material. The Natural History by the Roman writer Pliny the Elder includes a few sentences about a volcanic glass called obsidian ( lapis obsidianus), discovered in Ethiopia by Obsidius, a Roman explorer. Pliny the Elder, Naturalis Historia 36,67 (AD 77) In the past, it was used to manufacture cutting and piercing tools, and it has been used experimentally as surgical scalpel blades. Obsidian is hard, brittle, and amorphous it therefore fractures with sharp edges. Together with rapid cooling, this results in a natural glass forming from the lava. The high viscosity inhibits diffusion of atoms through the lava, which inhibits the first step ( nucleation) in the formation of mineral crystals. These flows have a high content of silica, giving them a high viscosity. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. ən, ɒ b-/) is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth.
Whether you can sharpen an obsidian blade in one of our Nirey sharpeners is another question.Naturally occurring volcanic glass Obsidian A bit of a hard one to police in the kitchen. However, even the manufacturer of the medical-type obsidian blades recommended that ‘hard objects should be avoided’ and ‘twisting or lateral motions should not be employed’. One of the big advantages of smooth cuts (as one of our customers has already mentioned) is that wounds from sharp blades heal more quickly than more jagged cuts, and are less prone to infection. Obsidian knives have however been used in medical procedures where very precise cutting is required and where laser surgery is not available. Obsidian is not particularly hard (unlike diamond), it’s just capable of being very sharp. So why aren’t we all equipping our kitchens with obsidian knives? Obsidian knives are quite delicate and tend to be a little brittle, so they’re probably not your best choice for the rough and tumble of a kitchen, particularly where they might strike something hard. Since obsidian will fracture down to a single atom, it is claimed to have a cutting edge five hundred times sharper than the sharpest steel blade, and under a high magnification microscope an obsidian blade still appears smooth, whereas a steel blade has a saw like edge. The Mayan Indians are credited with using obsidian blades first 2,500 years ago, although Stone Age spear tips made of obsidian have been found elsewhere in the world. This stops it from forming a crystal structure and also introduces a form of ‘compressive strength’ which makes the material even stronger. Obsidian is a volcanic glass that is created when magma is pushed to the earth’s surface and is cooled very rapidly. Glass on the other hand is ‘amorphous’, so it does not have any natural planes to split, or cleave to, making it much more suitable for making sharp edges.Ī type of naturally occurring glass that has already been in use since the Stone Age as a blade is obsidian.
The difficulty is that diamond crystals tend to ‘cleave’ in what’s called an octahedral fashion, which doesn’t allow for a very sharp blade cross-section. The hardest material out there is diamond, so logically a diamond knife should be the sharpest type. So there is an element of practicality as well. The trade off, of course, as we’ve mentioned already in our article about Samurai swords, is that very sharp blades can be very brittle, and it’s no use to anyone if parts of a knife break off while it’s being used. Leaving aside our knives of course, there are many earnest scientific discussions/arguments on the web as to which material makes, or would make the sharpest blade. Which brings us to the oft discussed topic of the sharpest blade in the world. If anyone has earned the right to be a bit nerdy about knives, then it’s us.