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WHAT TO LOOK FOR
Color: Unlike diamonds whose value is usually based in great part on its lack of color, colored gems get their beauty from their color. Especially if that color is rich and vivid. The most obvious component of color is the hue (its spectral color; ie: blue or green). Tone is important too: a very dark and almost black-blue sapphire, as well as a very pale washed out one, are less valuable and usually not as beautiful as a blue with a medium tone. The third factor is saturation. An intense, pure green tourmaline will win out over a dull, muted green almost any time.

Cut: Even a stone with exceptional color can look boring and lifeless if it’s cut poorly. There’s much more variation in proportion when cutting colored gems than there is with diamonds. This is usually due to trying to get the best color out of the rough crystal. Sometimes it’s taken too far: due to sloppy faceting techniques or in trying to cut the biggest stone from the crystal. In these cases, you’ll see large lifeless dark areas and/or large washed out areas. The brighter the flashes of color, the better the cut.

Clarity: Colored gems fit into 3 classifications:
≈ those that almost never have inclusions, such as topaz and tanzanite
≈ those that often have some inclusions, including sapphire, ruby, amethyst, garnet
≈ those that almost always have inclusions; just two: emerald and red or pink tourmaline

Clarity is not as important here as it is with diamonds; color is the priority.

Carat Weight: As with diamonds, the value of a rarer gem rises quickly as the carat weight increases. Oddly enough, sometimes the per carat price of a less valuable stone (for example, amethyst) can decrease as the size increases (as when a stone is too large and cumbersome to use in jewelry). Different varieties have different specific gravities (meaning some are denser/heavier than others). A one carat ruby will be smaller than a one carat tourmaline or diamond, because the ruby has the higher specific gravity. Stated a little differently, a 6mm round ruby will weigh more than the exact same size diamond.

Hardness: I’ve included hardness here because I believe that while jewelry needs to be beautiful, it must also be practical so it can be worn without worry. Hardness is the ability to withstand scratching. As we all know, diamonds are a 10 on the Mohs hardness scale. Talc represents a 1, and most gemstones fall in the 6 to 9 range. Ruby and sapphire are 9, but note that the scale is only relative: diamond is approximately 50 times harder than ruby and sapphire. The most common mineral, quartz comes in at 7. When you get to a pearl which has a hardness of just 3, you know to take special care of it.

But there’s another component: toughness. This is a stone’s ability to withstand chipping and cracking from a sharp blow. Tanzanite has a hardness of 8, but it’s not a good ring stone because it’s not tough. Same goes for emerald and opal. All need a protective setting if worn as a ring, and need to be treated with extra care.

More Information: There is an excellent website designed by the International Colored Gemstone Association which gives a wealth of information on gemstones by variety or color, famous gems, symbolism, photos etc. You can find it at www.gemstone.org.