![]() This transformation of obsidian is accelerated by the presence of water. Exceptionally old obsidians include a Cretaceous welded tuff and a partially devitrified Ordovician perlite. Because obsidian is metastable at the Earth's surface (over time the glass devitrifies, becoming fine-grained mineral crystals), obsidian older than Miocene in age is rare. Crystalline rocks with a similar composition include granite and rhyolite. Obsidian consists mainly of SiO 2 ( silicon dioxide), usually 70% by weight or more. Though obsidian is usually dark in color, similar to mafic rocks such as basalt, the composition of obsidian is extremely felsic. 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. Origin and properties Obsidian talus at Obsidian Dome, California Polished snowflake obsidian, formed through the inclusion of cristobalite crystals 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, granting 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. ![]() Usually black sometimes green or brown rarely yellow, orange, red or blue Turn your dream jewelry into something real at Fire Mountain Gems and Beads.For other uses, see Obsidian (disambiguation). We’ll also assist with getting the right hardware and accessories such as chain extenders, chain findings, clasps and jump rings. Call, email or use live chat Monday-Friday with generous hours to serve fellow jewelry enthusiasts. Our team is happy to help you find the right links for designer jewelry at the right prices. Finished chains have an elegant ready-to-wear look while unfinished chains give more of a rustic feel. You can get crystal, glass and gemstone chains, too. Base metal jewelry links that offer strength and affordability - or choose precious metal jewelry chains made of karat gold and sterling silver. These decorative chain styles make them an instant standout. ![]() In addition to popular cable jewelry chains and curb chains, there are ball chains oval links, serpentine chains and many others. You may not have even realized there are so many types of jewelry chains until you browse our online catalog. We have all sorts of jewelry chains for sale with bulk ordering and wholesale prices for anyone who’s passionate about jewelry making. Turn a short chain into a fastener or wear pendants, watches and keys around your neck attached to a stylish chain. Made of interconnected links, a jewelry chain can be worn as-is or used as the foundation for embellished bracelets and necklaces. When you need a chain for your jewelry creation - or a thousand chains to stock store shelves - you can find them at Fire Mountain Gems and Beads. Jewelry Chains and Links - Fire Mountain Gems and Beads
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