RocksdayMoonstone vs Opal
How to tell them apart
A feldspar made of microscopic alternating layers that scatter light into a soft, floating blue-white glow called adularescence.
Photo: Didier Descouens, CC BY-SA 3.0
Hydrated silica with no crystal structure. In precious opal, stacked microscopic spheres split light into flashing rainbow patches.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
Key differences
- Opal shows patches of spectral colors rather than one floating sheen.
Side by side
| Property | Moonstone | Opal |
|---|---|---|
| Type | Mineral | Mineraloid |
| Mohs hardness | 6–6.5 | 5.5–6.5 |
| Luster | Vitreous to pearly | Vitreous to waxy |
| Streak | White | White |
| Colors | White, Gray, Orange | White, Black, Orange |
| Crystal system / structure | Monoclinic | Amorphous |
| Specific gravity | 2.56–2.59 | 1.9–2.3 |
| Formula | (K,Na)AlSi₃O₈ | SiO₂·nH₂O |
| Found in | Sri Lanka; India | Coober Pedy, Australia; Lightning Ridge, Australia |
Properties that are the same for both are grayed out.
How to identify moonstone
- A milky glow that seems to float just under the surface.
- The glow moves as you tilt the stone.
- Flat cleavage faces on rough pieces; hardness about 6.
Crystal system: Monoclinic
Full Moonstone guide →How to identify opal
- Flashes of spectral color that shift as you turn it.
- Waxy to glassy luster.
- Light in weight for a gemstone.
- Common opal lacks color play and looks milky.
Structure: Amorphous
Full Opal guide →More comparisons
Could you tell them apart from a blurry close-up?
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