Synthetic emeralds bear such a close resemblance to the genuine gem that it is unwise for the inexperienced jeweler to attempt to distinguish between the two by means of inclusions. Natural emeralds often show three-phase inclusions (solid, liquid and gas within the same space). Colombian emeralds have tiny square crystals in the spaces partially filled by liquid and gas. Pyrite crystals are common in natural emerald. The Chatham synthetic usually contains crystals of platinum. These cubic crystals are white, in contrast to the brass yellow of the pyrite crystals in the natural. They are usually close to the surface. Platinum is soft and sectile, in contrast to hard, pyrite. A needle point will distinguish between the two in crystals at the surface. Chatham synthetic emeralds, as well as Gilson and Zerfass products, also are characterized by the presence of wispy or veil like groups of flux inclusions. The appearance illustrated is unlike any pattern observed in genuine emerald; but for the novice, the lower property values in conjunction with strong fluorescence under long-wave ultra-violet furnishes a safer means of identification.
The synthetic emerald-coated beryl (Lechleitner) is characterized by parallel cracks in the thin coating. Within the large preformed seed, natural beryl inclusions are to be expected. The overgrowth is not polished on most facets, so tiny crystal faces are visible under magnification.
The more recent hydrothermal synthetic emeralds developed by Linde lack the wispy inclusions that characterize the flux-fusion products. Instead, they have tiny two-phase inclusions. Often, they have larger phenakite crystals with cuneiform spaces extending from them.
By definition, would be manmade ruby produced by using fragments of natural ruby. Apparently, sintering was never used; Kurt Nassau, Ph.D., proved that the color is driven off and that it is not possible to sinter natural ruby fragments into material with the color and texture of ruby. However, it is apparent that small button-shaped synthetic rubies were made before the advent of the Verneuil process. Such synthetic ruby had sets of curved striae meeting other sets at abrupt angles. A some what similar striae condition could exist at the tip of modern boules started on synthetic seeds.
A number of materials with a wide variety of compositions have been made with structures identical to the garnet group, but with compositions unknown in nature. Almost every color of the spectrum has been made. Yttrium-aluminum and yttrium-iron garnet structures have been mentioned most often, but many other elements have been used to achieve desired results, mostly for laser research. Many of these have gem-substitute potentiality, but to date only substitutes for demantoid have appeared at GEM Laboratories in finished jewelry. Since natural garnets in other colors are inexpensive, the high cost of the synthetics made to date have, precluded wide use in other colors.
The inclusions in YAG include not only gas bubbles, but rather irregular appearing fingerprints. In addition to a few spherical inclusions that are somewhat akin to what one would expect in synthetic corundum, there are tube like inclusions reminiscent of those of synthetic spinel .(FIG 40)
Spherical or elongated gas bubbles and swirl marks, or flow lines, characterize glass. The latter are caused by incomplete mixtures of the ingredients of the melt or are formed by pressure as the glass is molded into its faceted - gem appearance.
Often, insoluble angular material is mixed with glass to simulate the genuine inclusions of certain species of gemstones. Such inclusions are seldom an accurate representation of those of the genuine gem and they are invariably accompanied by many bubbles, but a hasty examination may lead to an incorrect identification. Glass is often flawless.
The spherical gas bubbles that characterize synthetic corundum and synthetic spinel are also to be found in synthetic utile. The most unusual feature of the material under magnification is the tremendous doubling of opposite facet junctions and of any inclusions that may appear. In even small faceted stones, the birefringence causes two entirely separate culets to be seen.
Rock crystal quartz has been made synthetically by hydrothermal methods for many years. It is widely used, especially in the communications field. To our knowledge, this has not been used to any extent for jewelry purposes. In the last few years, synthetic quartz has been made in a variety of colors, both in Russia and the United States. Not only are citrine and amethyst colors manufactured, but also blue and green transparent quartz that does not resemble anything known in nature. Some of the stones can be identified by color banding parallel to the flat seed plate that was used to get the growth started. The banding may give a kind of heat-wave effect parallel to the seed. Although many are without inclusions, sometimes there are breadcrumb or dust like inclusions, or spicules similar to those that characterize hydro-thermal synthetic emerald.
Synthetic turquoise made by Pierre Gilson has been on the market for several years. It is readily distinguished by its appearance under magnification of about 50x. Under very high magnification, it is seen to be made up of darker blue spheres in a white ground mass.
SYNTHETIC ALEXANDRITE (Flux-Grown)
Synthetic alexandrite (Flux-Grown) is rather easily separated from natural material by the presence of inclusions of a typical flux-grown appearance either in veil like patterns or as tubes of flux, There are also tiny cut-corner triangular or hexagonal platelets that appear metallic. The synthetic is strongly fluorescent. (FIG 42)
There is a new synthetic alexandrite made by a pulling technique that shows characteristics of that method of growth. Certain directions of flatly curved striae are visible. Gas bubbles are possible but were not frequently seen in the few specimens that we had a chance to examine. Those specimens were quite light in color.
This Verneuil product is similar to the others in that it usually contains spherical gas bubbles.
It is manifestly impossible to convey by word alone a
sufficiently accurate description of characteristic inclusions so
reader will be able to identify a gemstone simply on a basis of its appearance under high magnification. The purpose of this chapter is to call to the attention of the reader the possibilities of the use of a gem's inclusions as a means of identification that will become increasingly valuable to him as he becomes more adept at gem testing.