Double Flow Obsidian Identification Guide
Identify double flow obsidian by its two distinct color zones in one glassy stone, with hardness, fracture, and look-alike tests.
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What Double Flow Obsidian Looks Like
Double flow obsidian is volcanic glass that records two distinct lava flows or color zones in a single piece — for example black and mahogany, or black and brown, meeting along a sharp contact. The two zones differ in color due to differing iron oxidation and inclusion content, but both share the same glassy, conchoidally fracturing obsidian nature.
Key visual cues:
- Color: two contrasting zones — commonly black with mahogany/brown, sometimes black with gray or tan.
- Contact: a visible boundary or band separating the two flows.
- Luster: vitreous (glassy) throughout.
- Transparency: translucent on thin edges, opaque in mass.
Step-by-Step Field-ID Checklist
- Confirm a glassy matrix with vitreous luster and conchoidal (shell-like) fracture.
- Identify the two flow zones meeting at a contact — the defining feature.
- Test hardness. It scratches glass (Mohs ~5–6).
- Check the break for sharp, curved conchoidal surfaces.
- Hold a thin chip to light — obsidian transmits light at thin edges.
Diagnostic Tests
- Mohs hardness: ~5–6 (glass); scratches window glass.
- Streak: white.
- Fracture: conchoidal, producing razor-sharp edges.
- Density: ~2.35–2.6 g/cm³.
- Acid: inert to dilute HCl.
- Magnetism: generally none.
Common Look-Alikes and How to Tell Them Apart
- Mahogany obsidian: shows brown/red streaks but typically as swirls within one mass rather than two discrete flows meeting at a contact; double flow shows two clearly separated zones.
- Banded/rainbow obsidian: banding/sheen is internal layering or iridescence rather than two distinct compositional flows.
- Snowflake (devitrified) obsidian: carries white spherulites; double flow obsidian is defined by color-zone contact, not spherulites.
- Apache tears: small rounded obsidian nodules, single-toned; not two-zone.
- Manufactured glass/slag: lacks natural flow contacts and may show bubbles or mold marks; obsidian shows natural conchoidal break and translucent edges.
Where It Is Found
Double flow obsidian occurs in silicic volcanic flows where successive or differently oxidized lava layers welded together. It is collected in young volcanic regions, notably the western United States (Oregon, Nevada, Arizona, California) and Mexico. Look for it as float and broken flow blocks in obsidian-bearing rhyolitic terrain; it is a descriptive variety name rather than a distinct mineral.
Frequently asked questions
How can you tell if it's double flow obsidian?
Look for a single glassy, conchoidally fracturing stone showing two distinct color zones meeting at a contact, hardness ~5–6 that scratches glass, and translucent thin edges. The two-flow boundary is the defining trait.
What does double flow obsidian look like?
It looks like glassy black obsidian with a second contrasting zone — often mahogany or brown — separated by a visible boundary representing two lava flows.
Is double flow obsidian the same as mahogany obsidian?
Not exactly. Mahogany obsidian has brown swirls within one mass, while double flow obsidian shows two distinct flow zones meeting at a clear contact.
How is double flow obsidian different from regular obsidian?
Regular obsidian is a single color or texture, while double flow obsidian preserves two separate lava flows or color zones in one piece.