|Gem Price per Carat
Most gemstones are priced according to weight. The exceptions are some carvings and cabochons, which may be sold by the piece rather than by the carat, since the work required to produce them exceeds the cost of the material. For the vast majority of gemstones, the price is calculated on a per carat basis. One gemstone carat is 200 mg. Carat, a measure of weight, should not be confused with karat, which refers to gold purity.
The price per carat of different gemstones can vary enormously, from as little as one dollar to tens of thousands of dollars per carat. Many factors influence the price per carat of gems. Here is a concise summary of the 10 factors that determine gem prices:sapphire, ruby, emerald, tsavorite garnet, tanzanite, spinel and alexandrite, command extremely high prices, due to their superior characteristics and rarity. Other varieties, such as many types of quartz, are abundant in many locations around the world, and prices are much lower. While the gem variety sets a general price range for a stone, the characteristics of the specific gem also have a major effect on the price per carat.
2. ColorIn colored gemstones it is color that is the single most important determinant of value. Ideal colors vary by gem variety of course, but generally, the colors that are most highly regarded are intense, vivid and pure. Gems that are too light or too dark are usually less desirable than those of medium tones. Thus, rich cornflower blue color in sapphire is more valuable than inky blue-black or pale blue.
3. ClarityGemstones that are perfectly 'clean' with no visible inclusions are usually priced higher. In general, the cleaner the stone, the better its brilliance. So while it is true that higher clarity grades are more highly valued, inclusions that don't interfere with the brilliance and sparkle of a gem do not significantly affect value. It is also worth noting that some gems, such as emerald, typically have inclusions.
4. Cut and PolishGemstones should be cut with proper proportions to maximize the light that is returned to the eye. But gem cutters or lapidaries often have to make compromises when cutting a particular piece of material. If the gem color is quite light, cutting a deeper stone will provide a richer hue. Conversely, a dark tone can be lightened by making a shallower cut. In every case, the facets should meet cleanly and the surface should be well polished with no scratches.
5. SizeFor some gemstone varieties, such as quartz, the price per carat is fairly constant as the weight of the stone increases. But in the case of many rarer gems, price does not increase in a linear fashion as the weight increases. Indeed, for some gems, such as diamonds, the price per carat can increase exponentially as the gem size increases. Therefore, a 1 carat stone may cost $1,000 while a 2 carat stone may cost $4,000. This means that good quality sapphires and rubies in larger sizes tend to have a much higher price per carat.
Not only are larger stones more expensive, but gems cut in stock sizes (known in the trade as calibrated sizes), also tend to be more expensive. This is because more material has to be removed to achieve the calibrated size.
6. ShapeSome shapes tend to be priced higher than others, this is partly due to demand and partly because of material issues with regard to cutting specific shapes. In general, round gems tend to command a high price. Rounds are much less common than ovals, since ovals are usually cut to preserve as much of the raw material as possible. Cutting a round gem normally requires a greater loss of rough material and for very expensive materials like sapphire, ruby, alexandrite and others, this can have a significant effect on price.
7. TreatmentGem treatments such as heating, fracture-filling, irradation and diffusion significantly improve the appearance of many gemstones, and these treatments are now routine for many commercial-grade stones. A treated stone is always less valuable than a similar untreated stone. Most of the stones that are routinely treated - such as ruby and sapphire - are now very rare in untreated form, and the untreated stones fetch a market price out of the reach of most consumers. If untreated stones are preferred, there are many choices. A number of popular gems, such as tourmaline, spinel, amethyst and garnet are almost never treated.
8. OriginStrictly speaking, a fine natural gem is a fine gem, regardless of its origin. Yet, in reality, certain gem varieties from locations such as Burma, Kashmir, Sri Lanka and Brazil, command a premium price. It is difficult to say whether this is justified, especially with so many fine gems coming from Africa.
9. FashionSome gems, such as blue sapphire, are always in fashion. Other gems become fashionable for short periods, which results in price increases. Recently we've seen andesine labradorite and color change diaspore in the spotlight. There has also been an increased interest in rutilated quartz. Some very fine gems, such as natural spinel actually have lower than expected prices because limited supply means that the gems are not heavily promoted.
10. Supply ChainThe gem trade is a business and everyone in the supply chain - from the mine to the jewelry retailer - is trying to turn a profit. Gemstones can pass through many hands on the way from the mine to the consumer, and the more brokers and distributors that handle the product, the higher the final price. This means that the same gemstone may carry a price that varies by as much as 200%, depending on where it is purchased.
- First Published: November-13-2008
- Last Updated: September-24-2014
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