Obsidian is a naturally occurring volcanic glass, and the answer to whether it is hard to find is nuanced. Globally, it is not a rare material, as significant deposits exist across the planet. However, its presence is strictly limited to areas with specific geological conditions, meaning it is impossible to find in vast regions of the world. For most people not living near a geologically active zone, a specimen is indeed hard to find without travel.
Defining Obsidian: Volcanic Glass
Obsidian is classified as an extrusive igneous rock, though it is fundamentally an amorphous solid, or natural glass. This means the atoms within the material are not arranged in the fixed, repeating pattern that defines a mineral crystal. Its glassy state results from the extremely rapid cooling of high-silica lava once it is expelled from a volcano. The lava that forms obsidian is felsic, characterized by a very high silica content, typically ranging from 65 to 80 percent by weight.
This high concentration of silicon dioxide makes the magma highly viscous, which inhibits the movement of atoms. When this viscous lava cools quickly, the atoms do not have sufficient time to organize into a crystalline structure before solidifying. The resulting material is brittle and fractures with a characteristic conchoidal break, producing curved, shell-like surfaces and edges that can be sharper than steel. While pure obsidian is usually dark, colors like mahogany, green, or rainbow sheen are caused by mineral inclusions or the alignment of tiny gas bubbles.
Geological Formation and Global Distribution
The requirement for a high-silica, viscous magma means that obsidian formation is directly linked to specific types of volcanism, usually associated with continental plate boundaries. These conditions are most often met in areas of subduction or rift zones where the continental crust melts to produce rhyolitic lava. Because the material is chemically unstable over geological time, it is rarely found older than a few million years. The glass slowly breaks down through a process called devitrification, meaning only areas with geologically recent volcanic activity will contain deposits.
Consequently, the global distribution of obsidian is highly localized, concentrating in regions like the Pacific Ring of Fire, the Mediterranean, and the western United States. Major sources are found in countries such as Japan, New Zealand, Iceland, Italy, Mexico, and the U.S. states of Oregon and California. Conversely, entire continents or large regions lacking recent volcanism, such as the eastern United States, have virtually no naturally occurring obsidian.
Practical Factors Affecting Collection
Even when a collector is physically located in a geologically rich region, finding a desirable specimen presents its own set of challenges. Obsidian is prone to weathering, and exposure to groundwater can cause hydration layers to form, which degrades the glass and makes it dull or opaque. Large deposits may also be buried by subsequent lava flows, volcanic ash, or sediment, requiring excavation rather than simple surface collection.
A significant practical difficulty is that while large quantities of common black obsidian may be easy to find in a flow, specific, high-quality varieties are much harder to locate. The rare types, such as gold sheen, rainbow, or snowflake obsidian, result from unique cooling conditions or specific mineral inclusions.
Safety and Legal Restrictions
Collecting obsidian safely requires caution due to its extreme sharpness, necessitating the use of gloves and eye protection to prevent injury from the brittle glass. Collectors must also be aware of legal restrictions. Collecting can be prohibited in national parks, on private property, or subject to specific limits on public lands like those managed by the Bureau of Land Management.