Clear Obsidian Identification Guide

What Clear Obsidian Looks Like

Clear obsidian is natural volcanic glass with very low iron and impurity content, giving it high transparency rather than the usual jet black. It ranges from nearly colorless to pale smoky gray or faint brown, and you can often read text through a thin flake. Its luster is bright and glassy (vitreous), it is amorphous (no crystals, no internal grain), and it breaks with smooth, curved conchoidal fracture producing razor-sharp edges. Surfaces frequently show swirl or flow banding even when the glass is otherwise clear.

Step-by-Step Field ID Checklist

1. Check transparency and color. Look for translucent-to-transparent material with a smoky or colorless tone, not opaque black.
2. Look at the fracture. Find a broken edge: a clean curved (shell-like) surface confirms glass, not a crystal.
3. Hold it to light. True clear obsidian transmits light evenly; look for internal swirls, gas bubbles, or stringers.
4. Test hardness. It should scratch glass but be scratched by quartz (Mohs ~5–5.5).
5. Feel the weight and warmth. Glass feels warmer and lighter than quartz; obsidian is not cold like crystalline quartz.
6. Inspect for bubbles. Round gas bubbles point to natural glass or slag; man-made slag usually has many uniform bubbles.

Key Diagnostic Tests

• Hardness: 5–5.5. A steel knife barely marks it; quartz (7) will scratch it.
• Streak: White.
• Fracture: Conchoidal, no cleavage. This is decisive against all crystalline minerals.
• Density: ~2.35–2.6 g/cm³, slightly lighter than quartz (2.65).
• No crystal faces: Amorphous glass never shows the flat hexagonal prism faces of quartz.
• Non-magnetic and shows no reaction to acid.

Common Look-Alikes and How to Tell Them Apart

• Clear quartz / rock crystal: Quartz is harder (7), often shows hexagonal prism faces and points, and feels colder. Quartz can show flat cleavage-like surfaces and is more rigid; obsidian only ever shows conchoidal fracture.
• Manufactured glass / slag: The hardest to separate. Slag is often too uniformly bubbly, may show mold marks, unnatural colors (bright blue, green), and a too-perfect clarity. Provenance from a known volcanic locality is the best confirmation.
• Smoky obsidian vs. smoky quartz: Smoky quartz is crystalline with defined faces and hardness 7.
• Apache tears: These are simply small rounded nodules of translucent obsidian; same material, different shape.

Where It Is Found

Clear and smoky-transparent obsidian forms where high-silica (rhyolitic) lava cooled rapidly with low iron. Notable sources include Glass Buttes in Oregon, parts of the Western U.S. (California, Idaho, Nevada), Mexico, and Armenia. Look in eroded rhyolite flows, talus slopes, and stream gravels.