Purple Sheen Obsidian Identification Guide
Identify purple sheen obsidian by its black glassy body with a purple iridescent sheen seen only when tilted in light.
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What Purple Sheen Obsidian Looks Like
Purple Sheen Obsidian is a volcanic glass whose body is black to dark gray but which displays a purple iridescent sheen when tilted under light. The sheen is caused by the scattering and interference of light off aligned layers of microscopic gas bubbles or mineral inclusions within the glass — the same effect that produces gold-sheen and silver-sheen obsidian, here tinted purple. The base material has a vitreous luster and breaks with a smooth conchoidal fracture.
The sheen is most visible on polished surfaces.
Step-by-Step Field ID Checklist
- Body color: Confirm a black/dark glassy stone.
- Tilt test: Rotate under a light source — a purple sheen should sweep across a polished face.
- Surface dependence: Note that the sheen appears as a surface effect, not color throughout the body.
- Fracture: Look for conchoidal fracture with sharp edges.
- Hardness test: It scratches glass weakly (Mohs ~5–5.5).
Key Diagnostic Tests
- Mohs hardness: 5–5.5.
- Streak: white.
- Cleavage: none; conchoidal fracture.
- Optical effect: the purple sheen is a reflection/interference phenomenon from inclusion layers, visible mainly on polished surfaces.
- Structure: amorphous glass, no crystal faces.
Common Look-Alikes and How to Tell Them Apart
- Purple obsidian: shows purple throughout the body (a transmitted color), whereas sheen obsidian's body is black with purple appearing only as a surface sheen on tilting.
- Gold/silver/rainbow sheen obsidian: same glass with a differently colored sheen; identified by the sheen color.
- Labradorite: a feldspar mineral with cleavage and a crystalline structure that shows blue-purple labradorescence; obsidian is glass with no cleavage.
- Manmade glass: may mimic sheen but often shows spherical bubbles and overly even effects.
Diagnosis: black glassy body + purple sheen on tilting + conchoidal fracture + no cleavage.
Where It Is Found
Sheen obsidians form in silica-rich volcanic flows where bubble or microlite layers align during flow. Purple sheen and related sheen obsidians are commonly sourced from Mexico (Jalisco) and other volcanic regions of the western Americas.
Frequently asked questions
What causes the purple sheen in purple sheen obsidian?
The sheen comes from light scattering and interference off aligned layers of microscopic gas bubbles or inclusions within the black volcanic glass, producing a purple shimmer on polished surfaces.
Purple sheen obsidian vs purple obsidian — what's the difference?
Purple sheen obsidian has a black body with purple appearing only as a surface sheen when tilted, while purple obsidian shows purple color throughout the body when held to light.
How do you identify purple sheen obsidian?
Tilt a black glassy stone under light to see a purple sheen sweep across the surface; confirm a hardness of 5–5.5, conchoidal fracture, and no cleavage.
Is purple sheen obsidian the same as labradorite?
No. Labradorite is a crystalline feldspar with cleavage that shows labradorescence, while purple sheen obsidian is amorphous volcanic glass with a sheen from inclusion layers.