Very often, inclusions are the only way to correctly identify whether a gemstone is natural, natural but treated, synthetic or man-made. This information is essential to gemmologists, gemstone suppliers, valuers and jewellers because their reputation depends on correctly identifying gemstones. A natural but treated gemstone, such as a ruby, may be subjected to different types of processes including heat alone, heating in a fluxing agent or a beryllium diffusion process.
A synthetic gemstone is manufactured and usually has the same chemical, physical and optical properties as the natural gemstone that it is imitating.
An imitation gemstone, such as paste, is also manufactured but does not have the same properties as the gemstone that it is imitating even though it may look similar or almost identical. The differences are evident in their inclusions.
Treatments for natural and synthetic gemstones are becoming very sophisticated and, although a variety of gemmological tests may be carried out to ascertain their true identity, the only correct identification is often by way of their inclusions.
As there are different methods of synthesising processes, including flux, hydrothermal and flame fusion – also known as Verneuil – the inclusions are different from one another and therefore can be used as ‘fingerprints’ to the identity of each method.
The world of inclusions is a fascinating one. They can be identified by using a 10X loupe or viewed at a higher magnification through a microscope. A fibre-optic light source, dark-field illumination and a polariscope can aid in the identification and the results can be not only revealing but captivating and addictive.
Take ruby as an example to demonstrate these differences. Observing a natural ruby under the microscope could reveal colourful, liquid films in between twinning planes (Figure 1), silk or rutile needles, boehmite needles, polysynthetic twinning or crystals either with or without a halo.
A heat-treated natural ruby may show similar inclusions to that previously discussed; however, there might be ‘snowballs’ (Figure 2) that appear as white, roundish, opaque inclusions containing one or more frozen bubbles and these immediately identify that the gemstone has been heat-treated.
A synthetic flux ruby may show flux fingerprints or flux particles – either white, yellow or orange – depending on the manufacturer. In Chatham synthetic flux rubies, acicular or hexagonal platinum platelets may also be visible and these are diagnostic for this manufacturer as they are believed to have formed as a result of the crucible in which they have been grown.
A man-made gemstone simulating a ruby usually has bubbles, swirls or mould marks.
Inclusions are surely a gemmologist’s best friend. It is essential that those testing gemstones understand and recognise the differences between natural, natural but treated, synthetic and man-made gemstones. Correct identification is critical not only because of the disparate prices of natural and synthetic gemstones but to the reputation of practising gemmologists.