A true gemstone must fulfill three parameters- beauty, durability, and rarity.
Beauty is self evident although not everyone can agree on what constitutes beautiful. But beauty alone does not make a gemstone.
Durability is a combination of hardness and toughness. Hardness is a gemstone's ability to resist scratches while toughness deals with the resistance to breakage. A diamond is the hardest gemstone with a hardness of 10 on the Mohs Scale but it is can be shattered by sharp blow. The Mohs Scale is relative hardness rating where the higher number will scratch a lower number.
So to be a true gemstone suitable for jewelry, a hardness nearly equal to or greater than the hardness of dust is needed. Dust is mainly finely powder quartz, which constitutes about 60% of the earth's crust, that has a hardness of 7 on the Mohs Scale. There are gemstones that are being touted on various medias as gemstones that aren't suitable for jewelry such as apatite with a hardness of 5, diopside with a hardness of 5.5, or flourite with a hardness of 4.
As always there are exceptions to every rule, but any softer gemstone should be mounted and treated with care. Opals have an average hardness on the Mohs Scale of 6 and peridot and demantoid garnets have a hardness of 6.5. and, while used in rings throughout history, are more prone to dulling of the surface. These are considered true gemstones and can be quite costly.
The last parameter is rarity, and this can be a really tricky. Diamonds are not rare. Natural color diamonds are incredibly rare and can be the most expensive gemstones. A 5.00 carat natural vivid pink flawless diamond recently sold at auction for $10,600,000.00 and natural blue diamonds routinely fetch more than $250,000.00 per carat. Many diamonds that are mined are only suitable for drill bits and abrasives. White diamonds are still regulated by a cartel to keep there values some what inflated but this last economic downturn has made them much more affordable.
A gemstone needs to be scarce and known. The best example is the color change gemstone type. Everyone has heard of alexandrite, the variety of chrysoberyl which ideally changes from bluish green in sunlight or fluorescent light to purplish red in incandescent or candle light. 100% color change alexandrites are extremely rare and extremely expensive, but even rarer are color change garnets that sell for a fraction of an alexandrite's price because they are so rare they will never have the consumer demand of the alexandrite.
I would also like to mention that there are synthetics and many treatments on today's market which make relatively worthless common place materials look like a rare gemstone. Gems & Gemology had several articles addressing these problems including several rings purchased from a TV jewelry dealer that used colored epoxy cement to enhance the color of tanzanites and amethysts and an antique pendant which had a glass filled composite ruby as the center stone.
So lets see, just because a stone is pretty doesn't make it a gemstone. Just because a stone looks good in a ring dosesn't mean it is a gemstone. And just because a gemstone is rare doesn't make it expensive.
The bottom line is buy from someone you trust and ask them to educate you about what you are buying. An educated consumer is the smartest buyer.
Last updated on August 30, 2010 by Francis M Lynch