The use of obsidian in jewelry often leads to questions about its classification, particularly whether it qualifies as a “precious stone.” This uncertainty stems from a misunderstanding of how gems are formally categorized in geology and gemology. While “precious” implies rarity and high monetary value, the traditional definitions are specific and restrictive. Understanding obsidian requires examining its geological identity.
The Formal Classification of Gemstones
The designation of a “precious stone” is based on centuries-old tradition, not modern geological metrics. Historically, only a select few materials were granted this distinction due to their rarity, durability, and beauty. These four stones—diamond, ruby, sapphire, and emerald—remain the only gems traditionally classified as precious.
All other materials used for adornment are grouped as “colored stones” or “ornamental stones,” replacing the outdated term “semi-precious.” The modern gemological community avoids the “precious” and “semi-precious” labels, as many colored stones, such as tanzanite or garnet, can be more valuable per carat than a low-quality diamond. Obsidian does not meet the hardness or composition requirements for the traditional “precious” group. It is considered an ornamental material, reflecting its physical properties as a rock rather than a mineral crystal.
Obsidian’s Geological Identity
Obsidian is not a precious stone because its fundamental structure is non-crystalline, a defining characteristic of most true gemstones. It is correctly identified as an extrusive igneous rock, a form of natural volcanic glass. This glass forms when silica-rich lava cools so rapidly that atoms cannot arrange themselves into an orderly, repeating internal structure.
The resulting material is amorphous, meaning it lacks the crystalline lattice structure typical of minerals like quartz or diamond, and is classified as a mineraloid. Obsidian consists of 70% or more silicon dioxide, similar in composition to rhyolite or granite, but rapid cooling prevents crystallization. This lack of structure gives obsidian a characteristic conchoidal fracture, causing it to break with smooth, curved surfaces and edges that can be sharper than surgical steel. Due to its glassy nature, obsidian registers a low hardness of 5 to 6 on the Mohs scale, making it soft and brittle compared to precious stones.
Obsidian’s Enduring Appeal and Value
Despite its exclusion from the formal “precious stone” category, obsidian possesses enduring value rooted in its unique aesthetics and history. Its deep, lustrous, glass-like surface, typically jet black, makes it a popular choice for jewelry and ornamental objects. Varieties like snowflake obsidian, which contains white clusters of cristobalite crystals, or rainbow obsidian, displaying an iridescent sheen from trapped gas bubbles, are highly sought after.
The material’s practical value stretches back thousands of years, as its razor-sharp edges made it an invaluable resource for ancient peoples creating tools and weapons. Cultures like the Aztecs revered obsidian for its spiritual significance, using it for ritualistic knives and polished mirrors. Today, raw black obsidian is common and affordable, but specialized varieties and high-quality finished jewelry can command moderate prices, reflecting a market value based on beauty, craftsmanship, and cultural significance.