Defining Blue Obsidian
Obsidian is a naturally occurring volcanic glass, formed when felsic lava rapidly cools with minimal crystal growth. While most commonly black, obsidian can exhibit various hues depending on its composition and formation conditions. True blue obsidian is exceptionally rare, with its striking blue hue typically resulting from optical phenomena rather than inherent pigmentation. This blue color often appears as iridescence or chatoyancy, where light interacts with microscopic inclusions or thin-film interference within the glass structure. The effect is not uniform coloration but rather flashes or shifts of blue as the material is moved. It is important to distinguish natural blue obsidian from man-made alternatives, which are far more prevalent in the market. Many materials marketed as “blue obsidian” are often artificial glass, such as slag glass, or have been artificially colored. These manufactured versions typically display a consistent, sometimes vibrant, blue hue that lacks the dynamic optical play seen in genuine specimens.
Formation and Geological Context
Obsidian forms from the rapid cooling of viscous, silica-rich lava, preventing the atoms from arranging into a crystalline structure. This quick quenching occurs when lava flows into water or cools quickly on the Earth’s surface. The resulting rock is amorphous. For natural blue obsidian to form, specific and rare geological conditions must be present during this rapid cooling process. The unique optical properties that cause the blue flashes are often attributed to the presence of minute mineral inclusions, such as magnetite or ilmenite, or the formation of microscopic gas bubbles or voids aligned in specific patterns. These tiny structures interact with light, scattering certain wavelengths to produce the blue effect. The specific locations where natural blue obsidian is found are extremely limited due to the precise conditions required for its formation. Geologists have identified only a few occurrences worldwide where these particular geological circumstances converge. This scarcity underscores its uniqueness compared to more common forms of obsidian.
Key Characteristics and Appearance
Natural blue obsidian typically exhibits a deep blue to blue-black color, often appearing black until light strikes it at a particular angle. Its luster is distinctly vitreous, giving it a glass-like sheen. When broken, it displays a characteristic conchoidal fracture. The interaction of light with the internal structure of blue obsidian is what reveals its captivating blue flashes. This iridescence can range from subtle hints of blue to more pronounced, shimmering effects across its surface. The intensity and visibility of the blue depend heavily on the lighting conditions and the angle of observation. While generally opaque, some thinner pieces of blue obsidian may exhibit slight translucency at their edges. Its hardness is comparable to other obsidians, typically ranking around 5 to 5.5 on the Mohs scale, making it relatively brittle. The specific gravity of obsidian generally falls between 2.3 and 2.6, similar to that of common glass.
Distinguishing Authentic Blue Obsidian
Differentiating genuine blue obsidian from imitations requires close observation of its optical properties and physical characteristics. Authentic blue obsidian’s color is not uniform; instead, it appears as an iridescent flash or shimmer that shifts with light and viewing angle. In contrast, artificial blue glass or slag commonly exhibits a consistent, often vibrant blue throughout the material, lacking the dynamic play of light seen in natural specimens. Another common characteristic of slag glass is the presence of small, perfectly spherical gas bubbles trapped within the material. While some natural obsidian can have bubbles, they are typically irregular in shape and less numerous. The fracture pattern can also provide clues; genuine obsidian will always show a conchoidal fracture, whereas some artificial materials may break differently. Given its rarity, natural blue obsidian is often more expensive and less commonly available than its artificial counterparts. Verifying the source from reputable dealers is advisable for those seeking authentic specimens.