I totally agree with Shane McClure because I understand the methodology, but many don't. As always, the problem is finding consensus among the gem dealers, colored stone grading experts, retailers and consumers. Today the gem trade and lab gemologists are having a hard time finding the 'sweet words' to convey the 'good news' to the consumers in a tone that makes sense. Keep trying.
Shane F McClure (GIA) writes:
The visual characteristics that gemologists and gem traders look for when examining a gemstone—such as hue, tone, saturation, and diaphenity—are the direct result of geologic environment in which the stone formed. This environment determines the stone’s chemical composition, growth structures, and inclusions suites, all of which affect its overall appearance. These factors are common for all gems, but are particularly significant in corundum.
While many different types of growth environments are possible, for corundum they can be broadly categorized into two main groups: metamorphic and magma-related; the later will be referred to simply as magmatic in this abstract. The largest distinction between these environments is that the metamorphic corundum formed in the earth’s upper crust, whereas the magmatic corundum crystallized much deeper in the earth at mid-crust or lower-crust/mantle levels. Eruptive forces are necessary to transport corundum from the latter group to the earth’s surface (typically in all alkali basaltic magma), so it is referred to as magmatic. While these two broad categories of sources for corundum may be readily distinguished by a combination of standard gemological and advanced analytical techniques, they can also commonly be recognized visually by a knowledgeable observer.
Beyond these two broad source designations, there exists a potential to further classify rubies and sapphires of all colors based on their dominant inclusion features and other physical characteristics. These inclusion features may influence the face-up appearance of a ruby or sapphire. For example, ‘milky’ zonal clouds of submicroscopic particles are responsible for the soft appearance or ‘velvety texture’ of blue Kashmir sapphires. Other possible features are concentrations of rutile needles, platelets, and particles that are commonly referred to as silk, which are typical of rubies and sapphires from Mogok, Myanmar (Burma). Such features, although commonly associated with a specific geographic source (e.g., Kashmir or Myanmar), more accurately distinguish a particular type of ruby or sapphire. Each corundum type shares other properties—including absorption spectra, chemical trends, and growth structures—which may be encountered in stones from more than one deposit or country.
What is proposed here is a classification for rubies and sapphires using a system that is objective, repeatable, teachable and relevant. It does not attempt to pinpoint geographic locality or specific deposit, but it does provide information that directly relates to a stone’s appearance and position in the marketplace. The intent is to supply information to the trade that will be useful and consistent in representing their stones, which in turn should benefit the consumer as well.
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