Very beautifully spotted Snowflake obian tumbled in and from the USA.

Obsidian is a naturally occurring volcanic glass. The name derives from a Roman who was called Obsius and which in ancient times would have an obsidian-like stone found in Ethiopia. Obsidian is created at a rapid cooling of lava having a water content of up to 3-4%. If the content of volatile components (water, carbon dioxide) is higher arises pumice, because the gases as a blowing agent to work. The formation of volcanic glass is highly dependent on the viscosity of the liquid lava and this is in turn strongly influenced by the content of silicic acid. The higher the level, the slower the flowing liquid. Most obsidianen have a silica content of 70% or more and are therefore classified as ryolieten. Less often be found trachitische, andesitic and fonolithische obsidianen which have a lower silica content. The color of obsidian varies quite widely, depending on the impurities it contains. The color is most dark green to deep black, although granite with a similar composition is a light colored material. Usually very finely divided hematite or magnetite to the cause. Sneeuwvlokobsidiaan contains inclusions of spherical grown structures, most of feldspar or cristobalite, which are called spherulites. They are produced by spherical crystal growth from a single central urban growth. Obsidian is a meta-stable material which falls back on the long term, in its crystalline, more stable form. Volcanic glass is not known from the Paleozoic and Precambrian. In the Stone Age obsidian was a coveted commodity because it is razor-sharp cutting edges. It was used for knives and weapons. Today it is a popular material for works of art and it is also used as a gemstone in jewelry. It is then cut as if it is a crystal.