Blue Obsidian
The Rarest Volcanic Glass
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Quick Facts
Formation & Origin
Like all obsidian, blue obsidian forms when silica-rich felsic lava erupts and cools too rapidly for crystals to develop. The magma, typically at temperatures of 700 to 900 degrees Celsius, reaches the surface and solidifies within hours to days, trapping atoms in a disordered, glassy structure rather than a crystalline lattice. The silica content must be above 65% for the resulting glass to be classified as obsidian rather than basaltic glass.
The blue color in genuine specimens is extremely rare and results from specific conditions during cooling. Submicroscopic inclusions of minerals or nanoscale gas bubbles scatter light preferentially in the blue wavelengths, similar to how Earth's atmosphere scatters blue light. In some specimens, trace amounts of titanium or iron in specific oxidation states contribute to a blue-gray hue. The exact mechanism varies by locality. Some blue obsidian shows its color only when light passes through thin edges, appearing black in reflected light.
It is critical to understand that natural blue obsidian is one of the rarest obsidian varieties. The vast majority of bright blue material sold commercially as 'blue obsidian' is manufactured glass, typically soda-lime glass colored with cobalt oxide. Genuine natural specimens are subtle in color, never the vivid electric blue commonly seen in crystal shops.
Identification Guide
Genuine blue obsidian has a glassy, vitreous luster and conchoidal fracture typical of all obsidian. The blue color is subtle, often appearing as a blue-gray or pale steel blue rather than vivid blue. Thin edges may transmit light with a bluish tint. At hardness 5 to 5.5, it can be scratched by quartz but scratches glass easily.
Distinguish it from blue chalcedony, which has a waxy luster and lacks the sharp conchoidal fracture of glass. Unlike blue agate, genuine blue obsidian does not show banding. The most important distinction is from manufactured glass. Natural blue obsidian will show flow banding, tiny mineral inclusions, or subtle color variations under magnification, while manufactured glass is perfectly uniform. True blue obsidian feels slightly warm to the touch compared to manufactured glass, which feels colder due to different thermal conductivity.
Spotting Fakes
This is one of the most faked stones in the crystal market. Roughly 95% of material sold as 'blue obsidian' is manufactured glass colored with cobalt. Here is how to tell them apart. First, examine the color. Natural blue obsidian is pale blue-gray or steel blue, never vivid electric blue or aqua. If the stone is a bright, saturated blue, it is almost certainly man-made glass. Second, look for bubbles. Under 10x magnification, manufactured glass often contains perfectly round, spherical air bubbles. Natural obsidian may have elongated bubbles aligned with flow direction, but never perfectly round ones. Third, check the price. Genuine blue obsidian is very rare and commands collector prices of $50 or more per gram for confirmed natural specimens. A cheap tumbled stone or carved skull in vivid blue is manufactured glass. Fourth, test thermal conductivity. Glass made for imitation (soda-lime glass) conducts heat slightly differently than natural obsidian. Hold the stone to your lip. Manufactured glass will feel noticeably colder. Finally, ask the seller for locality information. If they cannot specify where the material was mined, treat it with skepticism.
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Cultural & Metaphysical Traditions
Presented as cultural traditions, not scientific evidence
In modern crystal practice, blue obsidian is associated with communication, truth-telling, and psychic development. Some practitioners use it for throat chakra work, believing the blue color resonates with self-expression. Ancient Mesoamerican cultures prized obsidian in all colors for mirror divination, though the blue variety was not specifically distinguished in historical records. Contemporary traditions recommend it for clearing mental confusion and enhancing intuition. Due to its extreme rarity, many metaphysical properties attributed to 'blue obsidian' may actually describe experiences with manufactured blue glass.
Metaphysical and “healing” associations are cultural traditions, not medical advice or scientific fact. Crystals are not a substitute for professional medical care.
Where It's Found
Rare pale blue-gray specimens from volcanic flows
Occasional blue-tinted obsidian from Cascade Range volcanic sources
Very rare blue-sheened specimens alongside other obsidian varieties
Price Guide
Good to Know
Scratch test: At hardness 5.5, Blue Obsidian resists scratching from a knife but can be scratched by quartz. Best for pendants and earrings rather than rings.
Global supply: Found in 3 notable locations worldwide, from Greece to Mexico.
Heft test: With a specific gravity of 2.35-2.60, Blue Obsidian feels lighter than most minerals. This lightness can help identify it.
Care & Safety
What blue obsidian can and cannot tolerate, based on its hardness (Mohs 5.5) and chemistry (SiO₂ (amorphous)).
Can Blue Obsidian go in water?
Yes. Blue Obsidian is not water-soluble and durable enough (Mohs 5.5), so plain water is fine for rinsing and cleaning with mild soap. Avoid prolonged soaking, which serves no purpose, and dry the stone afterward.
Can Blue Obsidian go in salt water?
Not recommended, even though blue obsidian itself is hard and not water-soluble. Salt is corrosive and mildly abrasive: it can dull a polished surface, attack metal settings, and crystallize inside small fractures as the stone dries. A brief dip will not destroy blue obsidian, but rinse it with fresh water afterward and dry it. For routine cleaning, plain water is the safer choice.
Sources & References
The mineralogical and gemological data on this page is drawn from and can be cross-checked against these external references.
- WikipediaObsidian on Wikipedia
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