Flame Obsidian Identification Guide

What Flame Obsidian Looks Like

Flame obsidian is a patterned variety of volcanic glass (obsidian) in which streaks and swirls of reddish-brown to mahogany iron oxide flow through the black glass, creating flame-like markings. The pattern forms from iron-oxide-rich bands swirled into the glass as the lava flowed and quenched. It overlaps strongly with mahogany obsidian, the flame variety showing more dramatic tongue-shaped color flows.

• Color: black glass with red-brown to mahogany flame streaks
• Luster: vitreous (glassy)
• Transparency: opaque to translucent on thin edges
• Form: massive glass with swirled iron-oxide banding

Step-by-Step Field ID Checklist

1. Confirm a glassy base — smooth, glossy, no mineral grains.
2. Look for flame-shaped mahogany/red streaks swirling through black glass.
3. Check for conchoidal fracture — curved breaks with razor-sharp edges.
4. Test hardness — about 5–5.5, scratched by steel.
5. Note translucency on thin edges, typical of obsidian glass.

Key Diagnostic Tests

• Mohs hardness 5–5.5: Softer than quartz; a steel knife and quartz scratch it. This separates it from flame jasper and flame agate (6.5–7).
• Fracture: Strongly conchoidal with sharp edges — the diagnostic obsidian break.
• Streak: White.
• Density: ~2.4 g/cm³.
• No cleavage and no crystals: Being glass, it lacks both — a quick separator from crystalline rocks.
• Acid: Inert.

Common Look-Alikes and How to Tell Them Apart

• Mahogany obsidian: Essentially the same material; flame obsidian is the marketing name for pieces with bolder flame-shaped color flows. Both are black-and-mahogany obsidian.
• Flame jasper / flame agate: These are quartz-family (Mohs 6.5–7) and crystalline/microcrystalline; flame obsidian is glass (Mohs ~5–5.5) with conchoidal fracture. Hardness and fracture distinguish them cleanly.
• Rainbow / fire obsidian: Sheen varieties whose color is iridescent and angle-dependent, not the fixed red-brown pigment streaks of flame obsidian.
• Smoky glass slag: Manufactured glass may mimic the look but often shows bubbles and mold lines; natural obsidian shows flow banding and no manufacturing marks.

Where It Is Typically Found

Flame and mahogany obsidian form where rhyolitic lava rich in iron oxide bands cools too fast to crystallize. Major sources include the western United States (Oregon, Nevada, Utah, California, Arizona) and other young felsic volcanic regions such as Mexico. Look for it in obsidian flows and weathered float scattered around rhyolite domes and volcanic fields.