Obsidian

What causes the color: The black color comes from finely dispersed iron and magnesium oxide impurities, including microscopic magnetite crystallites, distributed through the glass. Where cooling and mineral content vary slightly, related varieties show sheens or bands (gold, silver, rainbow, or reddish mahogany tones) from different inclusion patterns.

How it forms: Forms when silica-rich (felsic) lava cools so rapidly — typically at the edges of lava flows or volcanic domes exposed to air or water — that there isn't time for the melt to organize into mineral crystals before it solidifies, trapping the material in a disordered, glassy state.

Treatments & imitations: Rarely treated in the crystal trade since it's already natural glass; the various sheen varieties (gold sheen, silver sheen, rainbow) are natural inclusion/bubble-layer effects rather than treatments. Manufactured black glass is occasionally sold as obsidian, though the two materials are chemically similar enough that the distinction matters more for authenticity than safety.

Real vs. fake: Genuine obsidian breaks with a distinctive conchoidal fracture — smooth, curved surfaces radiating from the impact point, the same fracture pattern that made it prized for prehistoric tool-making, since it can be knapped into edges sharper than surgical steel. Man-made black glass can share this fracture too, so the more reliable natural-vs-manufactured test is checking for genuine sheen/inclusion patterns and buying from a source that discloses origin, since visually the two can be very close.

Historical use: Aztec and other Mesoamerican cultures polished obsidian into mirrors used in divination, associated with the deity Tezcatlipoca ('Smoking Mirror'), and knapped it into ceremonial and sacrificial blades prized for their extreme sharpness; across the wider ancient world, obsidian was one of the most valuable trade materials for toolmaking well before metal tools existed, given how much sharper an obsidian edge is than flint or metal.

Metaphysical tradition: Modern crystal-healing tradition treats obsidian as a strong grounding and protective stone, traditionally paired with the root chakra, and often reached for during 'shadow work' — reflective practice on difficult emotions or patterns, echoing its historic use in scrying mirrors for looking inward.

How to use it: Commonly kept near an entrance or workspace for grounding, carried during difficult emotional processing, or (in raw polished sphere/mirror form) used as a meditative focal point echoing its historical use in divination mirrors.

Cleansing & care: Obsidian's conchoidal fracture means it can chip along unexpectedly sharp edges if knocked hard, so handle polished pieces carefully. It's safe for a brief rinse with water but should be dried promptly and not exposed to sudden temperature swings, which can stress the glassy structure.