Identification guide · Minerals
How to Identify Dioptase
Dioptase forms small, glassy, rhombohedral crystals of vivid emerald to bluish-green color with a vitreous luster and a pale green streak. Its hardness of 5 makes it noticeably softer than true emerald, and it has perfect cleavage in three directions, causing crystals to break apart easily under pressure. It typically occurs as druzy crusts on matrix rather than large single crystals. Dioptase is distinguished from emerald primarily by its lower hardness, brittleness, and the cleavage that emerald, a form of beryl, does not share.
Dioptase identification checklist
| Color | Emerald green, Bluish green | 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 | Transparent to translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5 | A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. |
| Streak | Green | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect rhombohedral | |
| Fracture | Conchoidal to uneven | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 3.28–3.35 | Heavier than it looks (specific gravity about 3.315). |
| Crystal system | Trigonal |
Extra tests for Dioptase
Glass check. Dioptase 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.
Dioptase look-alikes and how to tell them apart
Feldspar is harder (Mohs 6–6.5) than Dioptase (Mohs 5), so Feldspar will scratch Dioptase and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Dioptase vs Feldspar →
Dioptase is harder (Mohs 5) than Calcite (Mohs 3), so Dioptase will scratch Calcite and not the other way round. A copper coin (Mohs 3.5) scratches it, but a fingernail does not. Dioptase vs Calcite →
Albite is harder (Mohs 6–6.5) than Dioptase (Mohs 5), so Albite will scratch Dioptase and not the other way round. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not. Dioptase vs Albite →
Both sit near Mohs 5, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Dioptase identification FAQ
How can you tell if a rock is Dioptase?
Check the color (emerald green and bluish green), the vitreous luster, a Mohs hardness of 5 and a green streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Dioptase?
Dioptase has a Mohs hardness of 5. A steel knife blade (Mohs 5.5) scratches it; a copper coin does not.
What is the difference between Dioptase and Feldspar?
Dioptase (Mohs 5, vitreous luster) and Feldspar (Mohs 6–6.5, vitreous to pearly luster) look alike, but hardness, streak and heft usually separate them. See the full Dioptase vs Feldspar comparison for a side-by-side table.
Is Dioptase worth anything?
Entry-level Dioptase specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Dioptase?
Dioptase is most often emerald green and bluish green. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
