What is Gem ?

Everyone Agree with the statement that Diamond, ruby, sapphire, Amethyst, Topaz, Moonstone and emerald are gems. Opal is a gem, as are jade, lapis, garnets, and turquoise. However, what do we do with andalusite, diopside, and sphene? A material, to be considered a gem, must have beauty, durability, and scarcity, according to most accepted authorities, but all of these terms are subjective and open to wide interpretation. Opal, a gem, has hardness of only 5.5 on Mohs’ scale, which is really too soft to wear in a ring. Opal is also quite fragile and brittle and may crack spontaneously because of internal dehydration. If durability is a major criterion, opal is not a very good gem.

Yet it is a gem and has always been considered as such because of its other properties and beauty. Proustite, a silver arsenic sulfide, is a rare mineral that is seldom faceted, and then only for collectors. Its red color is one of the richest in the mineral kingdom, far surpassing in intensity the hue of most rubies. Anyone who sees a cut proustite is likely to comment on its great beauty. There may be fewer than fifty cut proustites in the entire world, so the scarcity factor is indisputable. Is a cut proustite a gem or not?

Zoisite has been known as a mineral for decades. It is usually gray or pinkish and opaque and seldom cut, even by collectors of the unusual. Then in the late 1960s fine, blue-violet, transparent zoisite crystals were discovered in Tanzania, and a few stones were cut from them. The cut stones were sold to a few collectors and connoisseurs of unusual faceted minerals. Eventually one of the world’s major jewelry establishments. Tiffany & Co., noted that cut blue zoisite resembles fine sapphire, dubbed the new material tanzanite and launched a major promotion of the “new gemstone.” Today, tanzanite is accepted as a gem and large stones bring rather high prices. Here is an example of a mineral that was not a gem by accepted criteria before 1967 but became a gem by promotion. This is a double standard that leads one to ask for an objective criterion in the definition of a gem. The dictionary is again consulted, and we find that a gem is “a precious or sometimes semiprecious stone cut and polished for ornament.” If we omit the terms relating to price, as discussed earlier, we have the basis of a simple and unambiguous definition.