Obsidian is a natural glass formed when lava, rich in silica, cools so quickly that mineral crystals do not have time to form, resulting in an amorphous structure. This volcanic glass has been valued for thousands of years for its ability to fracture into extremely sharp edges. Because its appearance is similar to common industrial byproducts and man-made glass, it is frequently imitated with materials like dyed glass, resin, or slag. These fakes are often difficult to distinguish from genuine obsidian, making practical inspection methods necessary for buyers and collectors.
Inherent Properties of Real Obsidian
Genuine obsidian possesses characteristics that set it apart from manufactured glass. Due to its density and thermal conductivity, authentic specimens will feel noticeably cooler to the touch than typical glass or plastic fakes, which tend to warm up quickly.
The defining structural signature of obsidian is its fracture pattern, known as conchoidal fracture. When broken, it produces a smooth, curved surface that resembles the ripples of a seashell. While glass also exhibits this fracture, the quality of the break is often more pronounced in natural obsidian.
Natural inclusions provide important clues that are difficult for manufacturers to replicate. True obsidian may contain microscopic gas bubbles, which are frequently stretched or elongated in parallel lines due to the movement of the flowing lava before it solidified. These aligned bubbles sometimes create a shimmering effect, leading to varieties like gold or rainbow obsidian. Other natural inclusions, such as minute, radially clustered crystals of cristobalite, create the distinct white patches seen in snowflake obsidian.
Simple Comparison Tests for Authenticity
One of the most immediate checks involves comparing the specimen’s weight to a known piece of glass of similar size. Although both obsidian and manufactured glass have a comparable specific gravity, natural obsidian often feels marginally heavier for its size than the lower-density glass used in many fakes. This subtle difference in density can sometimes be perceived by simply holding the piece in your hand.
A more definitive test involves examining the stone’s transparency under a bright light source. While genuine obsidian is largely opaque, thin edges of an authentic specimen will usually transmit light and appear translucent, often with a smoky brown or gray tint. Fakes, particularly those made from dyed glass, may remain completely opaque or transmit light with an unnatural or vibrant color, such as blue or green, which are extremely rare in nature.
Close inspection of any trapped air pockets is a reliable method for verification. Using a jeweler’s loupe or a strong magnifying glass, carefully look for any internal bubbles within the glass structure. If the bubbles are numerous, perfectly spherical, and uniformly distributed, the piece is likely a manufactured glass fake. In contrast, the few bubbles found in real obsidian are more likely to be irregular, teardrop-shaped, or stretched into thin cylinders due to the pressure and movement of the original lava flow.
A final test relates to the material’s hardness. Obsidian ranks between 5 and 5.5 on the Mohs scale, which is slightly harder than typical window glass. While genuine obsidian can scratch common glass, it can also be scratched by a steel object, such as a knife blade or a steel nail. This test should only be performed cautiously on an inconspicuous area, as an easily scratched surface suggests a softer material like plastic or resin.