Gemstone turquoise imitation

Turquoise gemstone imitation

The beautiful blue and blue-green colours of turquoise have been favourites for centuries. As early as ancient Egypt (around 5,500 BC), turquoise was used in jewellery — it was the first known gemstone used in jewellery. And even then, imitations of turquoise were already being made. The turquoise-blue faience (a type of pottery covered with tin glaze) figurines from that period are well-known.

In 1970, Gilson (known for synthetic opal, emerald and lapis, among others) introduced imitation turquoise. But how do you recognise imitation turquoise?

Identification of imitation turquoise

• Refractive index: turquoise and synthetic turquoise range between 1.610 and 1.650, imitation howlite between 1.586 and 1.605, and magnesite between 1.509 and 1.700
• Matrix veins: in turquoise, the veins are more irregular in shape and lie slightly lower than the turquoise stone. In the synthetic variant, the matrix is even and at the same height as the synthetic material. These are minimal differences but certainly visible with a loupe.
• Specific gravity: natural and synthetic turquoise between 2.38 and 2.88, imitation howlite between 2.45 and 2.58, and magnesite between 3.00 and 3.20

Impregnated turquoise

To stabilize or strengthen turquoise, it can be treated with wax or plastic.

• Refractive index: depends on the treatment, ranges between 1.56 and 1.60
• Spotty surface (but this also occurs with synthetic turquoise)
• Specific gravity: between 1.80 and 2.60
• Heating (destructive!): a melting reaction can indicate a wax or plastic treatment

Simulant or imitation

What is a simulant or imitation, exactly? A natural gemstone or man-made gemstone material that mimics another gemstone and can be used as a substitute. The imitation has a different chemical composition, crystal structure, and optical and physical characteristics. The most famous might be the red spinel in the British state crown, which was mistaken for a ruby for years, or the colourless cubic zirconia, which bears a visual resemblance to diamond.