Peanut Obsidian Identification Guide

What Peanut Obsidian Looks Like

Peanut obsidian is a volcanic glass (obsidian) with a black to dark gray base scattered with rounded tan, gray, or brown spots — spherulites of radiating cristobalite/feldspar crystals that grew as the glass began to devitrify. The spots resemble peanuts or peanut shells, giving the stone its name. It has a bright vitreous (glassy) luster, conchoidal fracture, and is translucent at thin edges.

Quick visual cues

• Glassy black body with round tan/brown spotty inclusions
• Bright glass luster and smooth shell-like fractures
• Spots are 3D spherical clusters, not surface patterns
• Sharp, razor-like broken edges

Step-by-Step Field ID Checklist

1. Confirm glassy luster and smooth, curved (conchoidal) fracture surfaces.
2. Look at the spots: rounded radiating spherulites embedded in the glass, often with a fibrous internal structure.
3. Test hardness: obsidian is 5-5.5 Mohs; it scratches glass weakly and is scratched by quartz.
4. Check for cleavage: none — only conchoidal fracture.
5. Hold to light: thin edges are translucent gray-brown.
6. Streak: white.

Key Diagnostic Tests

• Mohs hardness: 5-5.5.
• Streak: white.
• Cleavage/Fracture: none / conchoidal with sharp edges.
• Specific gravity: ~2.35-2.6, light.
• Texture: amorphous glass with no visible mineral grains in the matrix (spherulites are the exception).
• No acid reaction.

Common Look-Alikes and How to Tell Them Apart

• Snowflake obsidian: also spherulitic, but spots are typically whitish-gray and snowflake-shaped; peanut obsidian spots are larger, rounder, and tan-brown.
• Flower/spiderweb obsidian: spherulites form web or radiating patterns rather than discrete peanut-like blobs.
• Black agate/chalcedony: harder (7), denser, and has banding rather than embedded spherulites.
• Apache tears: translucent rounded obsidian nodules without the tan spotting.
• Manufactured slag glass: often shows gas bubbles and unnatural color swirls; obsidian is more consistent and natural-edged.

The decisive separators are glassy luster + conchoidal fracture + hardness 5-5.5 + embedded round spherulites, which together confirm devitrified obsidian rather than agate or glass.

Where Peanut Obsidian Is Found

Spherulitic obsidians come from young volcanic regions including Mexico (notably the Durango/Jalisco area), the western USA (Oregon, California, Arizona), and other rhyolitic volcanic fields. The spherulites form when silica-rich lava cools quickly to glass and then partially crystallizes around nucleation points.