I can separate Topaz and Aquamarine by the naked eye.
I have heard this sentence many times. Only I cannot do this by the naked eye, or only with a portion of doubt. Usually I measure the refractive index. It is also possible to measure the specific gravity, or a chelsa filter will give some clues.
| Pale blue stones | Refractive index | sepecific gravity |
|---|
| Aquamarine | RI 1.577 - 1.583 | 2.67 - 2.71 |
| Topaz | RI 1.610 - 1.638 | 3.53 - 3.56 |
Spinel and
synthetic Spinel | RI 1.712 - 1.736 | 3.58 - 3.61 |
In addition, light blue synthetic spinel's appear perfectly identical to the eye as topaz or aquamarine. The synthetic flame fusion spinel's are recognized with the polariscope due to the tension related false double refraction. Natural and synthetic spinel's are otherwise identical in composition and optical properties.
| Pale blue stones | Chelsea Filter | Internal tentions |
|---|
| Aquamarine | greenish blue to pale blue | none |
| Topaz | pale yellowish to colorless | none |
Synthetic Spinel
flame fusion by Verneuil | pale pink | tentions or internal strains |
| Flux grown Spinel | | none |
| Natural Spinel | no reaction | none |
The results of the Chelsea filter are not conclusif and need to be confirmed with an other test.
To rely on color only, for the determination of precious stones, is risky. I prepared a set of gemstones and invite you to test yours skills. This set is at your disposition for visual inspection at the following mineralshows.
Hubert Heldner April 2004
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