Spiderweb Obsidian

Spiderweb Obsidian is a patterned form of obsidian, natural volcanic glass, named for the network of thin grey, white, or brown lines that branch across its glossy black surface like a cobweb.

The webbing usually comes from healed fractures, devitrification (tiny crystallites beginning to grow), or fine flow banding intersecting at angles. Each piece is unique, and the contrast between the matte web and the mirror-black glass makes it a favorite for cabbing.

As an amorphous glass it has no crystal structure and fractures conchoidally, producing the smooth curved surfaces and sharp edges typical of all obsidian.

Like other obsidian, Spiderweb Obsidian forms when silica-rich (rhyolitic) lava cools so rapidly that mineral crystals cannot form, freezing into glass at or near a volcano's surface.

The web pattern develops in a few ways: micro-fractures that later fill with mineral matter or differently colored glass, or the early stages of devitrification where microscopic crystals (spherulites and crystallites) begin nucleating along cracks and flow surfaces. Stress as the glass cooled and contracted helps create the branching, net-like geometry.

It is found wherever silicic volcanism occurs, with much commercial material sourced from Mexico and the western United States.

Identify it by a black glassy base laced with a connected network of fine grey-to-brown veins forming an irregular web. Luster is vitreous and the fracture is conchoidal with sharp edges.

Hardness is about 5-5.5, so it scratches with a steel blade, and a thin chip is translucent brown at the edge. Streak is white.

Do not confuse it with dendritic agate or moss agate, which carry fern- or moss-like inclusions in a translucent chalcedony that is much harder (6.5-7). Spiderweb obsidian's pattern is a connected web in opaque black glass, and it is noticeably softer than any quartz-family stone.

Spiderweb Obsidian is cut into cabochons, beads, spheres, and small carvings; the web pattern is showcased in pendants and statement pieces. It polishes to a high gloss but chips like all glass, so durable settings are recommended for wear.

Plain obsidian has a long history as a tool and weapon material because freshly fractured edges are extremely keen.

Metaphysically, collectors consider obsidian protective and grounding, with the web variety linked to 'connecting' or clarifying scattered thoughts. These are traditional beliefs rather than proven effects.