Friday, 14 June 2013

Synthtic Spinel

Synthtic Spinel Gem stone
Magnesium aluminum oxide. Intact, the synthetic product nearly always has a different composition, which may vary from M90-2/U203 to Mgo-3Al203, or even MgO°4AI203. It was obtained by accident, using the Verneuil process, by adding M90 as a stabilizer to N203. In an attempt to produce more realistic-looking synthetic sapphires than were originally possible. it only came into use in 1920.

Crystal system


Cubic, like the corresponding mineral

Appearance


Synthtic Spinel CrystalLike the corundums produced by the Verneuil method. it is in the shape of a pedunculated pear or sausage, although it sometimes shows indications of cubic faces, giving it a squarish cross-section with rounded corners. It can be obtained in a wide range of colors of different intensities. Such as yellow Greenish yellow light green Blue-green, sky blue. Bright blue dark green turning to reddish violet. And colorless

Physical properties


Synthetic spinel has a slightly higher reiractive index (about 1.73) than natural noble spinel. The density is about 3.64 g/cm3. It has anomalous birefringence (probably due to excess alumina).


Production


Synthtic Spinel
Generally the same as the countries which produce synthetic corundum: France. Germany, Switzerland. Italy. Czechoslovakia. The Soviet Union. Japan and the United States. In some cases. The two are manufactured under the same roof.

This is much the most common type of synthetic spinel and is the main stone used to imitate aquamarine beryl.


Appearance


The color varies from soft pale blue to deep blue, but when viewed against a white ground. It often has a grayish or violet-gray tinge. it is perfectly transparent with strong luster. It is mainly given faceted, step cuts. Not always with truncated corners. Mixed round oval. And pear shaped cuts are used as well. Because synthetic spinel is hard but not brittle, extravagant types of cuts are also possible. Quite a frequent example being one that is roughly star-shaped. Another unusual cut often used on synthetic spine! is the "scissors" cut. Which is rectangular in shape? An elongated cross linking the corners of the crown. Stones of all sizes are found. From a fraction of a carat to 15-20 carats in weight.



Distinctive features

Synthtic Spinel GemThe color due to cobalt and therefore different from that of the natural gem, can easily be distinguished by an expert. Single refraction combined with a blurred. Cross hatched pattern due to anomalous birefringence, which is very obvious in polarized light. Is distinctive of this and all synthetic spinels. It has greater luster than the aquamarine it is intended to imitate. A star or scissors cut in a light blue stone is a warning sign. Although not a sure indication, that the stone is synthetic.


Cost

Very low and mainly due to the cutting process

Writer – Curzio Cipriani & Alessandro Borelli

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