Snowflake obsidian is obsidian gemstone with blotchy patterns of white or gray that visually resembles snowflakes. Typically it is carved into shapes that show off its coloration and often made into beads, eggs, hearts, pyramids, and spheres. It can be cut into cabochons and set in rings, pendants, and other reasonably-priced jewelry pieces. (A cabochon cut is a highly polished, rounded, convex form without facets.)
Obsidian's chemical composition is not well defined, but it is usually at least 70% silicon dioxide. It usually forms in magma that has been expelled from a volcano. Sometimes the magma cools so quickly that its atoms do not have a chance to form a crystalline structure. It becomes volcanic glass, usually black in color, with a smooth texture. Over time, obsidian may begin to crystallize. Radial clusters of gray or white cristobalite crystals form in some parts of the obsidian but not in others. It is these cristobalite crystals that resemble snowflakes.
When inclusions, or crystal impurities, are in obsidian, the glass may be green or brown. Rarely the inclusions, usually trace elements, make the glass blue, orange, red, or yellow. Sometimes light reflecting from the inclusions, or rock particles, or gas causes a metallic sheen, or iridescence, to appear on the obsidian. Depending on its color, iridescent obsidian is known as rainbow obsidian, golden obsidian, or silver obsidian, and is popular in jewelry.
Obsidian is found worldwide wherever there have been volcanic eruptions within the past two million years. Obsidian from eruptions over two million years old is likely to have been destroyed from weather, heat, or other processes. Locations of modern-day deposits of obsidian include Italy, Mexico, Scotland, and from the United States, Arizona, California, Colorado, Idaho, Texas, Utah, and Washington. (No states east of the Mississippi River have obsidian deposits because they have had no recent volcanic activity.)
Snowflake obsidian is sometimes called flowering obsidian or spherulitic obsidian, the latter appearing in some books from the 1800s. The term is usually not used today.