10mm Snowflake Obsidian bullet bracelet from the U.S.A.

Obsidian is a naturally occurring volcanic glass. The name is derived from a Roman named Obsius, who is said to have found an obsidian-like stone in Ethiopia in ancient times. Obsidian is formed by rapid cooling of lava with a water content of up to 3-4%. If the content of volatile components (water, carbon dioxide) is higher, pumice is formed, because the released gases act as a blowing agent. The formation of volcanic glass is highly dependent on the viscosity of the liquid lava, which in turn is strongly determined by the silicic acid content. The higher this content, the slower the liquid flows. Most obsidians have a silicic acid content of 70% or more and are therefore classified as rhyolites. Less commonly, trachitic, andesitic and phonolithic obsidians are also found, which have a lower silicic acid content. The color of obsidian varies quite widely depending on the impurities it contains. The color is mostly dark green to deep black, although granite with a similar composition is a light-colored material. Usually very finely divided hematite or magnetite are the cause of this. Snowflake obsidian contains inclusions of spherical grown structures, most commonly feldspar or cristobalite, called spherulites. They arise from spherical crystal growth from a single central growth nucleus. Obsidian is a metastable material that reverts to its crystalline, more stable form over time. Volcanic glass is therefore not known from the Paleozoic and Precambrian. In the Stone Age, obsidian was a coveted raw material because it forms razor-sharp cutting edges. It was used for knives and weapons. Today it is a popular material for art objects and is also used as a semi-precious stone in jewelry. It is then cut as if it were a crystal.