Obsidian forms when lava from a volcanic eruption cools rapidly with minimal crystal growth. Normally this cooling process creates a hard, uniform volcanic glass. But in some cases, the presence of small bubbles of water and steam cause snowflake obsidian to form.
As the lava flows during a volcanic eruption, small amounts of water and steam get trapped within it. When the lava cools quickly on the surface, these bubbles of gas have no time to escape. The water vapor freezes into small crystal clusters that expand and contract within the cooling lava. This expansion and contraction causes surrounding obsidian to fracture around the crystallized water bubbles. The resulting radial fractures create web-like patterns that look strikingly similar to snowflakes.
Another key factor is the chemical composition of the original lava. Snowflake obsidian only forms from lava that is high in silica, iron and magnesium. Rhyolitic lava that is more than 70% silica is most common. The high silica gives the lava a very thick, sticky consistency that enables it to trap bubbles as it flows before cooling into glass. A high iron and magnesium content promotes fracturing around the water crystal clusters. So snowflake obsidian requires just the right chemical mixture in order to form.
Where snowflake obsidian can be found also depends on the right volcanic conditions. It is typically formed in locations with rhyolitic lava flows, often in active continental volcanic regions. Well-known locations include Oregon and California in the United States, Armenia, and Mexico. The Big Obsidian Flow in the caldera of Oregon's Newberry Volcano is one of North America's largest sources of snowflake obsidian. Archaeological findings also place its earliest use with ancient Native American tribes like the Paiute, Aztec and Apache who used it to make weapons and cutting tools.
While beautiful examples of snowflake obsidian can be found at many sites worldwide, only about 1 in every 100 obsidian flows actually develops snowflake texture and patterning. That rarity adds to its value as a gemstone. Cabochons, spheres, bookends, and jewelry are common uses that showcase the distinctive snowflake effect. With care, snowflake obsidian can be skillfully knapped into arrowheads, spear points and blades similar to how ancient peoples used it. For rockhounds and gem lovers, finding a piece of snowflake obsidian in the wild is a rare treat.
The uniqueness of snowflake obsidian comes from a very specific combination of water, chemistry and rapid cooling. Its distinctive look has made it a popular decorative and spiritual stone since ancient times. Understanding how snowflake obsidian forms gives greater appreciation for this beautiful natural phenomenon. The next time you see a piece, imagine the volcanic forces that created its wonderful snowflake-like patterns.
