RocksdayAragonite vs Pearl
How to tell them apart
Same chemistry as calcite, different crystal structure. It builds pearls and seashells and forms spiky 'sputnik' clusters.
Photo: JJ Harrison (https://www.jjharrison.com.au/), CC BY-SA 4.0
A gem grown inside a mollusk from layers of nacre — aragonite and protein.
Photo: MASAYUKI KATO, CC BY-SA 3.0
Quick tests
- Acid (vinegar or dilute HCl): Aragonite fizzes; Pearl doesn't.
Key differences
- Pearl nacre is aragonite, but ordinary aragonite has no layered glow.
Side by side
| Property | Aragonite | Pearl |
|---|---|---|
| Type | Mineral | Mineraloid |
| Mohs hardness | 3.5–4 | 2.5–4.5 |
| Luster | Vitreous | Pearly |
| Streak | White | — |
| Colors | White, Orange, Brown | White, Pink, Black, Gold |
| Crystal system / structure | Orthorhombic | Organic (nacre of aragonite) |
| Specific gravity | 2.94–2.95 | 2.6–2.85 |
| Formula | CaCO₃ | — |
| Found in | Molina de Aragón, Spain; Morocco | Persian Gulf; Japan (Akoya) |
Properties that are the same for both are grayed out.
How to identify aragonite
- Fizzes in acid.
- Needle-like or six-sided twinned crystals.
- No rhomb cleavage, unlike calcite.
- Slightly heavier than calcite.
Crystal system: Orthorhombic
Full Aragonite guide →How to identify pearl
- Deep glow (orient) from overlapping nacre layers.
- Feels gritty when rubbed gently against teeth; imitations feel smooth.
- Cool to the touch at first.
Structure: Organic (nacre of aragonite)
Full Pearl guide →More comparisons
Could you tell them apart from a blurry close-up?
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