Synthetic alexandrite
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Synthetic alexandrite is an artificially grown crystalline variety of chrysoberyl, composed of beryllium aluminum oxide (BeAl2O4).
The name is also often used erroneously to describe synthetically-grown
Manufacture
Most true synthetic
Flux-grown alexandrite stones are expensive to make and are grown in platinum crucibles. Crystals of
The largest producer of jewelry quality laboratory-grown alexandrite to this day is Tairus. Production capacity is in the range of 100 kg/year.
Chrysoberyl-based synthetics
Czochralski or “pulled” alexandrite is easier to identify because it is very “clean”. Curved striations visible with magnification are a give-away. Some pulled stones have been seen to change color from blue to red – similar to natural alexandrite from Brazil, Madagascar, and India. Seiko synthetic alexandrites show a swirled internal structure characteristic of the floating zone method of synthesis. They have “tadpole” inclusions (with long tails) and spherical bubbles.
Flux-grown alexandrites are more difficult to spot because of their convincing colors, and because they are not “clean”. Their inclusions of undissolved flux can look like inclusions in natural chrysoberyl. However, layers of dust-like particles parallel to the seed plate, and strong banding or growth lines may also be apparent.[a]
The Inamori synthetic alexandrite had a cat's eye variety, which showed a distinct color change. The eye was broad and of moderate intensity. Specimens were a dark greyish-green with slightly purple overtones under fluorescent lighting. The eye was slightly greenish-bluish-white and the stones were dull and oily. They appeared to be inclusion-free and under a strong incandescent light in the long direction, asterism could be seen with two rays weaker than the eye. This has not been reported in natural alexandrite. Under magnification, parallel striations could be seen along the length of the cabochon and the striations were undulating rather than straight, again not a feature of natural alexandrite.
The name allexite has been used for synthetic alexandrite manufactured by the Diamonair Corporation who maintains that its product is Czochralski-grown.
Corundum-based simulated alexandrite
Most gemstones described as synthetic alexandrite are actually simulated alexandrite: Synthetic corundum laced with vanadium to produce the color change. This alexandrite-like sapphire material has been known for almost 100 years.
The material shows a characteristic purple-mauve color change which, although attractive, differs from alexandrite because there is never any green. The stones will be very clean and may be available in large sizes. Gemological testing will reveal a refractive index of 1.759–1.778 (
Footnotes
- ^ The crystals on the seed plane(s) of flux-grown alexandrites are not platinum, but rather silicon carbide from the furnace heating elements during crucible and nutrient changes.
References
- "Methods of producing synthetic alexandrite". alexandrite.net. Alexandrite tsarstone collectors guide. 7 September 2006. Retrieved 4 November 2006.
External links
- "Created alexadnrite". tairus.com.
- "Alexandrite synthetics and imitations". alexandrite.net.