Identification guide · Materials
How to Identify Opalite
Opalite is usually milky white, blue, and yellow with a vitreous luster and is translucent. 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 to colorless. It is most often confused with Glass, Slag Glass, and Smithsonite; the tests below separate them.
Opalite identification checklist
| Color | Milky White, Blue, Yellow, Opalescent | 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 | Translucent | 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 to colorless | 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 Opalite
Glass check. Opalite 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.
Opalite 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. Opalite vs Glass →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Opalite vs Slag Glass →
Opalite is harder (Mohs 5.5) than Smithsonite (Mohs 4.5), so Opalite will scratch Smithsonite and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Opalite vs Smithsonite →
Both sit near Mohs 5.5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Opalite vs Opal →
Field tips
- Look for milky translucent glass with blue-yellow glow and smooth manufactured polish.
- Check for bubbles or molded shapes that support a glass identification.
- Do not identify retail opalite as natural Opal unless play-of-color and provenance support it.
Opalite identification FAQ
How can you tell if a rock is Opalite?
Check the color (milky white, blue, yellow, and opalescent), the vitreous luster, a Mohs hardness of 5.5 and a white to colorless streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Opalite?
Opalite 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 Opalite and Glass?
Opalite (Mohs 5.5, vitreous luster) and Glass (Mohs 5.5, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Opalite vs Glass comparison for a side-by-side table.
Is Opalite worth anything?
Entry-level Opalite specimens sell for around $3, typical collector pieces about $15, and premium examples $70 or more depending on size, quality and locality.
What color is Opalite?
Opalite is most often milky white, blue, yellow, and opalescent. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
