Cobalt Blue Obsidian Identification Guide
Identify cobalt blue obsidian, an almost always man-made colored glass, and learn how to separate true natural obsidian from dyed or manufactured glass.
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What Cobalt Blue Obsidian Looks Like
Cobalt blue obsidian is a vivid, saturated blue glass, usually transparent to translucent with a bright vitreous luster. Important for accurate ID: deep, even cobalt-blue "obsidian" sold commercially is almost always manufactured (man-made) glass, not a natural volcanic product. Genuine natural obsidian with a blue appearance is typically a subtle structural sheen ("electric blue" or rainbow obsidian) caused by microscopic inclusions, seen at certain angles on otherwise dark glass — not a uniform see-through cobalt color. Recognizing this distinction is the core of identifying it.
Step-by-Step Field ID Checklist
- Assess the color. A uniform, transparent, intense cobalt blue strongly suggests manufactured glass.
- Backlight it. Even saturated color throughout with no natural swirl banding points to artificial glass; natural sheen colors shift with angle.
- Look for bubbles and mold marks. Rows of uniform bubbles or seams indicate manufactured glass.
- Inspect the fracture. Both natural and man-made glass show conchoidal fracture, so this alone won't separate them.
- Check hardness. ~5–5.5 for any silica glass.
- Consider provenance. Natural obsidian comes from volcanic localities; "cobalt blue obsidian" with no source is a red flag.
Key Diagnostic Tests
- Hardness: ~5–5.5 (glass). Quartz scratches it.
- Streak: White.
- Fracture: Conchoidal, no cleavage (true of all glass).
- Density: ~2.4–2.5 g/cm³.
- No acid reaction, non-magnetic.
- Key tell: Uniform transparent cobalt color = manufactured glass; angle-dependent sheen on dark glass = possible natural sheen obsidian.
Common Look-Alikes and How to Tell Them Apart
- Manufactured slag/art glass: This is what most "cobalt blue obsidian" actually is. Telltales: too-even color, abundant uniform bubbles, mold seams, and impossibly bright hue.
- Natural electric blue / rainbow obsidian: Appears dark in normal light but flashes blue or rainbow sheen at certain angles due to nanoscale inclusions — not a uniform transparent blue.
- Blue quartz / chalcedony: Crystalline, harder (7), feels cold, lacks glass bubbles.
- Blue glass beads/cullet: Same as manufactured glass; check for mold marks and uniformity.
Where It Is Found
Because uniform cobalt blue obsidian is essentially a manufactured product, it has no natural locality — it is made by coloring molten glass with cobalt. Genuinely natural obsidian with a blue sheen (electric blue, rainbow) is found at volcanic sources such as Glass Buttes (Oregon), Mexico, and Armenia. Always treat marketed "cobalt blue obsidian" as glass unless a credible volcanic source is documented.
Frequently asked questions
Is cobalt blue obsidian real or man-made?
Uniform, transparent cobalt blue "obsidian" is almost always man-made colored glass. Natural obsidian is not a saturated see-through blue; genuine blue obsidian shows only a subtle angle-dependent sheen on otherwise dark glass.
How can you tell if blue obsidian is fake?
Look for too-even color, rows of uniform bubbles, mold seams, and an impossibly bright transparent blue. These indicate manufactured glass rather than natural volcanic obsidian.
What does real natural blue obsidian look like?
Natural "electric blue" or rainbow obsidian appears dark in ordinary light but flashes blue or rainbow sheen at specific viewing angles, caused by microscopic inclusions — not a uniform transparent blue.
Cobalt blue obsidian vs blue quartz?
Blue quartz is crystalline, hardness 7, feels cold, and has no glass bubbles. Cobalt blue obsidian (glass) is softer (5.5), warmer, and often shows bubbles or mold marks.