Aquamarine vs Topaz: How to Tell Them Apart
Pale blue aquamarine and blue topaz can look alike, but topaz has a clearly higher refractive index and specific gravity, and its perfect cleavage makes it more fragile than its hardness suggests.
| Property | Aquamarine | Topaz |
|---|---|---|
| Mineral | Beryl (Be3Al2Si6O18) | Aluminium fluorosilicate |
| Typical colours | Pale blue to greenish blue | Colourless, blue, yellow, pink, orange |
| Mohs hardness | 7.5–8 | 8 |
| Toughness | Good | Poor |
| Refractive index | 1.577–1.583 | 1.609–1.637 |
| Birefringence | 0.006 | 0.009 |
| Optic character | Uniaxial – | Biaxial + |
| Specific gravity | 2.67–2.80 | 3.49–3.57 |
| Pleochroism | Weak to distinct (blue / colourless-blue) | Weak to distinct |
| Common treatments | Gentle heating to remove green tones is common | Most blue topaz is irradiated and heated; coatings also occur |
| Ultrasonic cleaning | Use caution | Avoid |
How to tell Aquamarine from Topaz
- DecisiveRefractometer. The refractive index ranges do not overlap (Aquamarine 1.577–1.583 vs Topaz 1.609–1.637), so a single reading separates them.
- DecisiveSpecific gravity. The SG ranges do not overlap (2.67–2.80 vs 3.49–3.57), so hydrostatic weighing or heavy liquids separate them.
- HelpfulOptic character. Both are doubly refractive, but Aquamarine is Uniaxial – and Topaz is Biaxial +. A conoscope or an optic-sign test on a refractometer can tell them apart.
- NoteTreatments. Aquamarine: Gentle heating to remove green tones is common. Topaz: Most blue topaz is irradiated and heated; coatings also occur.
Aquamarine vs Topaz for jewellery
Aquamarine has a Mohs hardness of 7.5–8 and good toughness; Topaz has a Mohs hardness of 8 and poor toughness.
Most blue topaz is irradiated and heated to reach its colour, while aquamarine's colour is natural, usually with only gentle heating.
Educational reference only. Typical published values vary between specimens and sources, and this page is not a gemological laboratory report. Confirm important stones with a recognised gem lab.
Frequently asked questions
What is the main difference between Aquamarine and Topaz?
Pale blue aquamarine and blue topaz can look alike, but topaz has a clearly higher refractive index and specific gravity, and its perfect cleavage makes it more fragile than its hardness suggests.
How can I tell Aquamarine from Topaz?
Refractometer: The refractive index ranges do not overlap (Aquamarine 1.577–1.583 vs Topaz 1.609–1.637), so a single reading separates them. Specific gravity: The SG ranges do not overlap (2.67–2.80 vs 3.49–3.57), so hydrostatic weighing or heavy liquids separate them.
Which is harder, Aquamarine or Topaz?
Topaz is harder: it is Mohs 8, while Aquamarine is Mohs 7.5–8.
Which is more durable for everyday jewellery, Aquamarine or Topaz?
Aquamarine has a Mohs hardness of 7.5–8 and good toughness; Topaz has a Mohs hardness of 8 and poor toughness. Toughness describes resistance to chipping and breaking, which matters as much as hardness for rings.
What are the refractive index and specific gravity of Aquamarine and Topaz?
Aquamarine: refractive index 1.577–1.583, specific gravity 2.67–2.80. Topaz: refractive index 1.609–1.637, specific gravity 3.49–3.57.
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