Stripe Obsidian Identification Guide
How to identify stripe (banded) obsidian by its flow-banded volcanic glass, conchoidal fracture, low hardness, and tests against agate and jasper.
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What Stripe Obsidian Looks Like
Stripe obsidian (banded obsidian) is volcanic glass (amorphous silica) displaying parallel or swirling stripes, bands of black, gray, brown, tan, or reddish color produced by flow layering and slight differences in composition or microcrystallite content as the lava cooled and flowed. It has a high glassy luster, conchoidal fracture, sharp edges, and translucency on thin edges. The banding is typically straight-to-wavy and follows the original lava flow direction.
Step-by-Step Field ID
- Check luster and break. Bright glassy shine with smooth, curved conchoidal fracture and razor edges.
- Look at the bands. Parallel or gently swirling flow stripes, often subtle differences in gray/brown/black.
- Backlight it. Thin edges transmit a brownish or gray glow; it is glass.
- Test hardness. Softer than quartz stones (Mohs ~5-5.5); it will not readily scratch glass.
- Feel for homogeneity. No visible interlocking crystal grains, just glass with color banding.
Key Diagnostic Tests
- Mohs hardness: ~5-5.5, will not scratch window glass cleanly (separates it from agate/jasper at 6.5-7).
- Streak: white.
- Fracture: conchoidal, sharp-edged, no cleavage.
- Specific gravity: ~2.35-2.6.
- Texture: glassy and homogeneous apart from flow banding.
Common Look-Alikes
- Banded agate: agate is crystalline silica, harder (Mohs 6.5-7, scratches glass), with concentric/fortification banding from chemical layering; obsidian banding follows flow lines and the material is glass (softer, conchoidal, glows on thin edges).
- Banded/ribbon jasper: opaque, harder (6.5-7), and crystalline, not glassy.
- Manufactured striped glass: may show air bubbles and overly regular bands; natural obsidian banding is irregular with flow swirls.
- Snowflake/starry obsidian: same glass but spotted with spherulites rather than striped.
Where It Is Found
Stripe obsidian forms in fast-cooled rhyolitic lava flows and is collected from young volcanic regions worldwide, including the western United States (Oregon, California, Idaho, Arizona), Mexico, Iceland, Armenia, and Indonesia.
Frequently asked questions
What does stripe obsidian look like?
It is glassy volcanic glass with parallel or swirling flow bands of black, gray, brown, tan, or red, showing a high luster, conchoidal fracture, sharp edges, and brownish translucency on thin edges.
How can you tell stripe obsidian from banded agate?
Obsidian is glass, softer (Mohs ~5-5.5, will not scratch glass) with flow banding and a glowing thin edge; agate is crystalline silica, harder (6.5-7, scratches glass) with concentric fortification bands.
What causes the stripes in stripe obsidian?
The stripes are flow bands, formed as silica-rich lava flowed and cooled with slight differences in composition, color, and tiny crystallite content along the flow.
Is stripe obsidian natural?
Yes, stripe (banded) obsidian is natural volcanic glass; watch for air bubbles and overly regular bands that would indicate manufactured striped glass instead.