Obsidian is a naturally occurring volcanic glass formed when molten lava cools so quickly that atoms do not have time to arrange into an organized crystalline structure. The short answer to whether obsidian can get wet is yes, but the concern is not chemical dissolution. The risks associated with water involve its physical properties, particularly its sensitivity to sudden temperature changes, which can lead to fracturing.
Understanding Obsidian’s Composition
Obsidian is classified as a mineraloid rather than a true mineral because of its amorphous nature, meaning it lacks a defined crystal lattice. Its chemical composition is primarily silicon dioxide (\(\text{SiO}_2\)), typically making up 70% to 75% of the material. This high silica content is similar to that found in manufactured glass.
Water does not react with this bulk silicate structure in a way that causes immediate damage or dissolution. The material is chemically stable, so exposing it to rain or briefly rinsing it will not cause it to break down. Brief contact with water is safe due to this chemical inertness.
The only chemical interaction water has with obsidian occurs over immense geological timescales, a process known as hydration. When exposed to the atmosphere, obsidian slowly absorbs moisture, forming a microscopic layer called a hydration rim. This diffusion process is so slow that archaeologists use the rim’s thickness to date ancient artifacts spanning thousands of years. For the average owner, this long-term process is not a practical concern.
Physical Risks of Rapid Temperature Changes
While water does not chemically harm obsidian, its temperature can cause physical damage due to thermal shock. Obsidian, like other types of glass, is a brittle material with a low coefficient of thermal expansion. This means the material cannot easily accommodate rapid changes in temperature through uniform expansion or contraction.
If a piece of obsidian is very hot and plunged into cold water, or if a frozen piece is exposed to hot water, the outer layer and inner core will attempt to change volume at different rates. This differential stress creates intense internal tension within the brittle structure. When the stress exceeds the material’s strength, the material relieves the tension by fracturing.
The result is often a conchoidal fracture, characterized by smooth, curved breakage surfaces. Even less extreme temperature differences can cause micro-fissures or “crazing,” especially in larger pieces or those already containing internal flaws. The danger is not the water itself, but the thermal gradient introduced by the water.
Guidelines for Handling and Cleaning
To safely clean or handle obsidian, the primary rule is to avoid temperature extremes. Always use lukewarm or room-temperature water when washing the material. This ensures the temperature difference between the water and the stone is minimal, preventing thermal shock damage.
A small amount of mild dish soap can be added to the water, and the obsidian should be gently cleaned using a soft cloth or soft-bristled brush. Avoid harsh household chemicals like bleach or ammonia, as these can dull the natural luster and potentially etch the surface.
After cleaning, the obsidian should be rinsed thoroughly with clean, lukewarm water to remove any soap residue. Pat the piece completely dry using a soft, lint-free cloth. Drying is especially important if the piece has small surface cracks or is kept in a cold environment, where trapped water could freeze and expand, leading to further fracturing.