 Understanding Gems
The beauty, rarity and historical mystique of gems are timeless. Their richly diverse varieties and colours come in a kaleidoscopic array.
Understanding the value of gems is essential to making a successful and rewarding purchase. Regardless of the gem variety you're buying, there are a few constant rules to bear in mind when selecting your gemstone jewellery purchases.
Gemstone Categories
The various gem categories used are Precious, Semi Precious, Rare and Museum. These are standard classifications based on value and rarity. For example, Precious Gems include those varieties (e.g. Emerald, Ruby etc.) with high market values, while Museum Gems include pieces suitable for collections. These are usually one of a kind piece, while Rare Gems are simply that, rarer lesser-known varieties.
Precious Gemstones
Only four gemstones are considered precious. These are the diamond, emerald, sapphire and ruby, which have retained their prized positions among jewels due to their extraordinary colours and extreme rarity. Precious gemstones with good colour and large size are very hard to come by. Because of their rarity, it is common to use stones with inclusions and blemishes in jewelry.
Semi-Precious Gemstones
A semi-precious gemstone includes any gemstone other than precious stones. The value of semi-precious gemstones can vary depending on the availability of the mineral; natural black opal, for example, is hard to come by and more valuable than most other semi-precious stones. As a rule, however, semi-precious stones are always more plentiful than precious stones. That makes it easier to find large, well-coloured, very clean stones appropriate for jewellery.
Colour
Colour is the single most important factor when evaluating colored gems. Basically, the more attractive the colour seen, the higher the value. Bright, rich and intense colours are valued over those that are too dark or light. The colors seen should ideally remain attractive regardless of prevailing light conditions. Whether viewed indoors, outdoors, by day or by night, a gem should always remain beautiful. Although specific colour hues can affect the prices of gems, personal preferences are also very important.
Optical Effects
Some gems exhibit unusual optical effects known as phenomena. These rare and beautiful effects very often add value to gems. The Cat’s Eye Effect, the Star Effect and the Colour Change Effect are very popular phenomena and are highly valued.
 | Chatoyancy
Chatoyancy or the Cat’s Eye Effect is a reflection effect that appears as a single bright band of light across the surface of a gemstone. |
Asterism
Asterism or the Star Effect is a reflection effect that appears as two or more intersecting bands of light across the surface of a gem. |  |
 | Colour Change
Colour change gems are those that distinctly change their colour when viewed under two different light sources. |
Iridescence
Iridescence is the rainbow like colour effects that are seen in some gems. Commonly found in Opals. |  |
 | Aventurescent
Aventurescent gems are those that have a colourful play of glittering reflections from small metallic inclusions. |
Cut & Polish
Unlike Diamonds, colored gems possess variable optical properties and are not cut to a uniform ideal. A well-cut colored gem exhibits even colour, a minimal number of inclusions, good brilliance and shows the majority of Carat weight when viewed from the top. A well-cut gem should also exhibit good symmetry and polish condition. Facets should be aligned straight in relation to the gem’s girdle and also to each other. Polish condition should be good with no visible surface pits and polishing lines.
Broadly, the styles of gem cutting can be divided into Faceted Gems (gems with geometrically shaped flat polished faces) and Non-Faceted Gems (those Gems that do not have geometrically shaped flat polished faces such as cabochons).
 Carat Weight
Gemstone weight is measured in Carats. This unit of measurement originates from the traditional use of carob seeds to weigh gems. Carob seed were used because of their consistent size and shape. One Carat is the equivalent of 0.20 Grams. Further divided into 100 smaller units known as Points.
As the weight of a gem increases, so does its price per Carat. Large gems are always rarer than smaller ones, so per Carat prices rise exponentially. A 3 Carat Ruby is always worth far more than three 1 Carat Rubies of the same quality.
Clarity
Most gems contain tiny natural features called inclusions. Mostly microscopic in nature, they are most easily glimpsed under magnification. Inclusions that don’t interfere with the brilliance, sparkle and fire of a gem don’t affect the value.
The clarity of gems is determined by judging the amount and location of inclusions seen. Basically, the higher the clarity grade, the higher the value of the gem.
Durability
Gems with better durability and resistance to wear are generally more highly prized than those of lesser durability.
Gemstone Classifications Natural Coloured Gemstones
Natural stones are courtesy of nature, with no interference from humans. Don't assume that just because it's natural a stone should carry a high price tag. Prices are driven by desirability, quality, and availability. A brilliantly coloured ruby with "perfect" clarity will cost thousands of dollars more than a garnet of similar quality.
Gemstone Treatment
Most natural stones are treated to improve appearance. Heat and radiation change or enhance colours. Diffusion deepens colour, but only within a stone's outer layers. Oil and waxes are used to fill-in surface-breaking fractures. Some treatments are permanent--others are not. Treated gems can be a good choice when you know what you are buying and pay a price that reflects a stone's true quality.
Why are Natural Gemstones Treated?
Most commonly treatments are used to improve the colour or appearance of the finished product, some gemstones simply would not exist in saleable quantities without treatment. For example, heating greenish brown Zoisite to 600 degrees Celsius produces the currently popular vibrant violet-blue Tanzanite. No heating, no Tanzanite!
Does Treatment affect a Gem’s Value?
Interestingly, in some precious and semi-precious coloured gemstones there is no variation between the value of treated and untreated material. In fact, treating may even increase a gems value. For example when vibrant violet blue Tanzanite is created, it commands a far higher market price then the original stone Zoisite.
Synthetic Coloured Gemstones
A synthetic stone shares a natural stone's physical, chemical, and optical qualities. The difference? Synthetics are created in a lab. They've been around for a long time, but modern technology allows us to grow stones that are difficult to distinguish from their natural counterparts. Ask for a lab certificate to verify authenticity before paying top dollar for a stone represented as natural.
Gem Treatments/Enhancements
Imitation Stones
Imitation, or simulated, stones may at first look like the real thing, but that's where the similarities end. They do not share physical characteristics with natural or synthetic stones. Many are made of glass or plastic and most can be detected easily by a jeweller.
Composite Stones
Doublets are stones that are assembled using a larger chunk of an inexpensive stone (or glass) which is topped by a thin slice of the genuine stone. The division usually isn't obvious without magnification.
Bottom Line
Imitation and synthetic stones make lovely jewellery……there's no reason to avoid them. What you do want to avoid is paying too much for a misrepresented stone. Read as many resources as possible and start looking more closely at jewellery when you are making purchases. |
