Thursday, 28 February 2013

Introduction to Synthetic Turquoise Gemstone

Cabochon of synthetic turquoise, 18 ct
Hydrated phosphate of copper and aluminum, This is manufactured from artificial raw materials, by a sintering process similar to that used for ceramics. It is fairly similar to natural turquoise in chemical composition and crystal structure; although the water content is lower, perhaps as a result of the production process.

Crystal system
Triclinic, but as this product is an aggregate of minute grains, the individual crystals can never be distinguished.

In bars or "ingots" obtained from k. mould, of a uniform, bright blue color very similar to that of the natural gem. It is also produced with a network of blackish veins.

Physical properties
It has a hardness 01 5.5 to 6, like the (rare) very good quality natural turquoise. It has a density of 2.60 to 2.75 g/cm3. As often happens with microcrystalline materials, only one refractive index is measurable; it is around 1.60.

Uncut synthetic turquoise, 80 mmAt the moment, synthetic turquoise is only produced in France.
48.1 Synthetic turquoise
The synthetic turquoise produced is used exclusively as an ornamental material.

It is usually very homogeneous, and a striking, light blue color. It takes a good polish like good quality natural turquoise, only very thin pieces are translucent. It is always cut into cabochons or spherical or polished pieces for necklaces. It is also produced with blackish veining, like some natural turquoise.

Distinctive features
It has the physical properties of good quality natural turquoise. Its hardness is, therefore, much greater than that of nearly all natural turquoise avail-able on the market. Under a microscope, or even a lens, a minute cellular pattern like hexagonal mesh is visible in one direction only, and this is the surest means of distinction. Unlike most natural turquoise nowadays, it is not treated with paraffin.

Quite low, several times lower than that of natural turquoise of similar quality and even a lot less than that of poor-quality natural turquoise.

Writer – Curzio Cipriani & Alessandro Borelli

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