Silver Sheen Obsidian

Obsidian is glass. Not window glass, but glass that a volcano made all by itself. According to Wikipedia, it forms when silica-rich lava cools so fast that the atoms do not have time to arrange themselves into crystals. That is why it is not considered a true mineral, but a "mineraloid". The photo shows two teardrop-shaped stones, greyish black, with a silver sheen running across both, like brushed metal.

That sheen is the whole story. According to Geology.com, obsidian sometimes has a metallic sheen caused by light reflecting from tiny inclusions of mineral crystals, rock debris or gas, and according to Wikipedia, gas bubbles aligned in layers as the lava flowed can produce such a sheen. So the silver you see is really a trace of flowing lava. And according to Wikipedia, its look depends on the direction of the cut: from one direction the stone is jet black, and from another it is glistening grey.

Glass breaks with a conchoidal fracture and very sharp edges, and people found that out early. According to Wikipedia, the first archaeological evidence of obsidian use, from Kenya, dates to about 700,000 years ago. It turns up in Israel too: at Gilat, in the western Negev, eight obsidian artifacts from the Chalcolithic period were found, and lab analysis traced them to sources in Anatolia. So even back then, someone bothered to haul glass from Turkey to the Negev.

And that sharpness is still useful. According to Wikipedia, an obsidian blade can be many times sharper than a steel surgical scalpel: its edge is about three nanometers thick, and it stays smooth even under an electron microscope. Some surgeons use it, although the US FDA has not approved it for use on humans. According to Wikipedia, some Aztec priests also used obsidian mirrors to conjure visions, and these mirrors were connected with the god Tezcatlipoca, whose name translates as "Smoking Mirror".

Just do not confuse sharp with tough. According to Geology.com, obsidian has a hardness of about 5.5, scratches easily, and breaks or chips on impact. So it suits earrings and pendants better than rings and bracelets.