Identification guide · Igneous Rocks
How to Identify Rainbow Obsidian
Rainbow Obsidian is usually black with rainbow sheen, purple, and green with a vitreous luster and is opaque. It has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Its streak is white. It is most often confused with Obsidian, Gabbro, and Peridotite; the tests below separate them.
Rainbow Obsidian identification checklist
| Color | Black with rainbow sheen, Purple, Green, Gold | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5.5 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | None | |
| Fracture | Conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.4 | Ordinary rock-like heft (specific gravity about 2.4), similar to quartz. |
| Crystal system | Amorphous |
Extra tests for Rainbow Obsidian
Glass check. Rainbow Obsidian shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Rainbow Obsidian look-alikes and how to tell them apart
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Rainbow Obsidian vs Obsidian →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Rainbow Obsidian vs Gabbro →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Rainbow Obsidian vs Peridotite →
Jasper is harder (Mohs 7) than Rainbow Obsidian (Mohs 5.5), so Jasper will scratch Rainbow Obsidian and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
Field tips
- Check whether the specimen's color and texture match typical Rainbow Obsidian examples.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Rainbow Obsidian identification FAQ
How can you tell if a rock is Rainbow Obsidian?
Check the color (black with rainbow sheen, purple, green, and gold), the vitreous luster, a Mohs hardness of 5.5 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Rainbow Obsidian?
Rainbow Obsidian has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Rainbow Obsidian and Obsidian?
Rainbow Obsidian (Mohs 5.5, vitreous luster) and Obsidian (Mohs 5.5, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Rainbow Obsidian vs Obsidian comparison for a side-by-side table.
Is Rainbow Obsidian worth anything?
Entry-level Rainbow Obsidian specimens sell for around $10, typical collector pieces about $50, and premium examples $200 or more depending on size, quality and locality.
What color is Rainbow Obsidian?
Rainbow Obsidian is most often black with rainbow sheen, purple, green, and gold. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
