White Obsidian Identification Guide

What White Obsidian Looks Like

White obsidian is a volcanic glass (chemically similar to rhyolite) in which devitrification has produced white, radial clusters of cristobalite/feldspar crystals (spherulites) within a glassy base. Pure all-white obsidian is uncommon; most 'white' material is pale gray to grayish glass densely speckled with white spherulites, grading into classic snowflake obsidian (white snowflakes in black glass). The luster is glassy (vitreous), and fresh surfaces show a brilliant conchoidal fracture with razor-sharp edges. It is opaque to translucent.

Key Visual Cues

• Glassy luster with smooth, curved (conchoidal) fracture
• White feathery or snowflake-like spherulites in a darker glassy ground
• Razor-sharp edges on fresh breaks
• No crystal faces, no banding from layered minerals

Step-by-Step Field ID Checklist

1. Check the fracture. Smooth, shell-like conchoidal breaks with sharp edges are the signature of glass.
2. Look for spherulites. White radial spots or snowflakes confirm devitrified obsidian.
3. Test hardness. It scratches glass faintly but is softer than quartz.
4. Heft and feel. Obsidian feels glassy and slightly warm compared to crystalline rock.
5. Inspect for bubbles or flow lines. Frozen gas bubbles and flow banding indicate volcanic glass.

Diagnostic Tests

• Mohs hardness: ~5–5.5 — softer than quartz; a steel file scratches it.
• Streak: White.
• Cleavage/fracture: No cleavage; pronounced conchoidal fracture.
• Density: ~2.35–2.6 g/cm³.
• Magnetism/acid: Non-magnetic; inert to acid.

Common Look-Alikes and How to Tell Them Apart

• Snowflake obsidian: The same material with a black base; 'white obsidian' simply has more or denser spherulites and a paler ground.
• White chalcedony / agate: Harder (Mohs 7), often translucent and waxy, and lacks the warm glassy feel; chalcedony will scratch obsidian.
• Milk glass (man-made): Very similar conchoidal fracture, but manufactured glass is uniform with mold marks and consistent color; natural obsidian shows spherulites, flow lines, and irregular shapes.
• White marble: Soft (Mohs 3), granular, and fizzes in acid; obsidian does not react.
• Pumice/perlite: Frothy, lightweight, and porous versus obsidian's dense, solid glass.

Where White Obsidian Is Found

Obsidian forms where silica-rich lava cools too fast to crystallize. Devitrified and snowflake varieties come from older flows where spherulites had time to nucleate. Sources include the western United States (Oregon, California, Nevada, Utah, Arizona), Mexico, and other young volcanic regions. Collect it in lava flows, perlite quarries, and weathered float.

Collecting Tips

Look for glassy nodules with white snowflake spots in old rhyolitic flows. Confirm by the conchoidal fracture and a hardness below quartz. Handle freshly broken pieces carefully — obsidian edges are extremely sharp.