Understanding Gemstones

The beauty, rarity and historical mystique of gems are timeless. Their richly diverse varieties and colors come in a kaleidoscopic array that puts Diamonds to shame. However, before you make a purchase, you will need a basic understanding of gems.

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.

What is A Gem?

For decades, the Gemological Institute of America (GIA) has taught their students that “gems are specimens of minerals or organic materials used for personal adornment that possess the attributes of beauty, rarity and durability”. The GIA teaches that all three of these attributes must be present - a gem lacking in one or more of these attributes risks losing its status as a gem.

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 color change effect are very popular phenomena and are highly coveted.
 

Adularescence

Asterism

Aventurescence

Chatoyancy

Color Change

Iridescence

Play of Color

Silk

Adularescence: Moonstone shows a blue-whitish opalescence (sometimes described as a “billowy” light) that glides over the surface of the gem. Interference phenomena from the gems layered structure are the cause of this effect.

Asterism: Also know as the star effect, this is a reflection effect that appears as two or more intersecting bands of light across the surface of a gem. It is usually created through reflection of light by thin fibrous or needle-like inclusions that lie in various directions. There are 6 ray, 4 ray and, rarely, 12 ray stars. Ruby and Sapphire cabochons can sometimes very effectively show this phenomenon.

Aventurescence: This is a colorful play of glittering reflections of small, plate or leaf-like metallic inclusions.

Chatoyancy: Also know as the cat's eye effect, this is a reflection effect that appears as a single bright band of light across the surface of a gemstone, similar to the slit eye of a cat. It is caused by the reflection of light by parallel fibers, needles or channels. One the most coveted cat's eye is Cat’s Eye Chrysoberyl - so much so, that if you just says cat's eye, it is assumed to be in reference to Cat’s Eye Chrysoberyl. All other cat's eye gems, such as those found in Tourmaline or Tigers Eye, typically have an additional designation.

Color Change: Color change gems are those that distinctly change their color when viewed under two different light sources. This phenomenon is found in Alexandrite, Sapphire and Color Change Garnet.

Iridescence: This is the rainbow like color effect seen in some gems and is caused by cracks or structural layers breaking up light into spectral colors. Fire Agate is a gemstone that shows this phenomenon to good effect. When iridescence occurs in metallic hues (called schiller) in Labradorite, it is commonly called “labradorescence”. In Pearls, iridescence is called the “orient”.

Play of Color: This is flashes of rainbow colors in Opal that change with the angle of observation. This should not be confused with “opalescence”, which is the milky blue or pearly appearance of Opal caused by the reflection of light.

Silk: Especially desirable in Rubies and Sapphires, this is the reflection of fibrous inclusions or canals that cause a silky appearance. 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 color, an acceptable number of inclusions, good brilliance and shows the majority of carat weight when viewed from the top.

 

	Table
Girdle		Crown
		Pavillion
	Culet (may or may not be faceted)
Industry Standard Anatomic Layout Of A Faceted Gemstone

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).

 

Antique Cushion	Baguette	Emerald Cut	Briolette
Heart Cut			Octagon Cut
Pear Cut	Common Cuts		Marquise Cut
Round Brilliant Cut			Oval Cut
Square Cut	Trilliant Cut	Round Cabochon	Princess Cut

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, the term carats is often confused with “karats”. Karat is a measurement of gold purity and has no relationship to the term carats, other than the fact that they both originate from the use of carob seeds, which in this case was used to weight the alloys added to gold.

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 exceptionally. For example, a 3 carat Ruby is always worth far more than three 1 carat Rubies of the same quality.

Gemstone prices also increase rapidly when in excess of certain key weights. For example, a 2.01 carat Ruby has a higher price tag than a 1.99 carat Ruby, despite a negligible difference in actual size. Gem pricing is said to suffer a “non linear scale of increments”.

Clarity

Most gems contain tiny natural features called inclusions. Mostly microscopic in nature, they are most easily glimpsed under magnification. While inclusions by definition are internal flaws in a gemstone, they often add character and individuality. Inclusions are also a fascinating hallmark of authenticity that records a gem’s natural relationship with the earth. 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. In general, inclusions that don’t interfere with the brilliance, sparkle and fire of a gem don’t affect the value.

In transparent gems, the degree of transparency and light return (brilliance) is considered crucial. However, through market experience, we learn to expect certain degrees of clarity from certain gems. For example, Aquamarine is generally expected to be clean and Emerald is expected to be hazy. Flawless, clean Emeralds are very rare.

“The love of precious gemstones is deeply implanted in the human heart,” George Kunz wrote in his book The Curious Lore of Precious Stones, “The cause of this must be sought not only in their coloring and brilliancy but also their durability.” Kunz further wrote, “The sheen and coloration of precious stones are the same today as they were thousands of years ago and will be for thousands of years to come. In a world of change, this permanence has a charm of its own that was early appreciated.” A gemstone must be durable enough not to break or fade over years of wear. Its brilliance and beauty are expected to last for a very long time, even to the point where a gemstone will outlast its owners and be passed on to sons and daughters, which, in turn, will help maintain its status as a gem and awaken appreciation in the succeeding generations. While gems with better durability and resistance to wear are generally more highly prized than those of lesser durability, given proper care all gemstone jewelry should be suitable to be passed down to many generations.

Rarity

While, scarcer gems are more highly prized than less scarce varieties, rarity does not always add value. Sometimes the rarity of a gem type jeopardizes commercial viability. Tsavorite Garnet is rarer than Emerald, is entirely free of treatments and is frequently more beautiful, but because there aren’t enough around, it cannot compete with Emerald in terms of the consumer’s perception of its value. Given the enormous Diamond stockpiles and new sources springing up around the world, when compared to many colored gemstones, Diamonds are not especially rare. Strict control of polished Diamonds on the market, combined with sophisticated consumer advertising, has elevated Diamonds to the extent that they are perceived as a rare and coveted product. If a gem variety is so rare that it is essentially unknown to the general public, it is often classified as an "exotic gem". Gems such as Boracite, Childrenite and Simpsonite are extremely rare, attractive and durable, but they are unlikely to command prices appropriate to their rarity because fewer people are aware of their existence.

Historical Connotations & Origin

While there are exceptions, gemstones that are rich in history and folklore are generally more prized than those lacking historical connotations. When specifying an origin, GemsTV undertakes a series of checks based on our experience to ensure that a gemstone displays the characteristics indicative of the origin specified. While GemsTV does everything possible to ensure that the origins we specify are correct, gemstone origin is considered a matter of opinion.

Pairs & Suites

Pairs or suites of gems matched for color, clarity and cut are valued more highly per carat or per gem than single gems of the same quality. Given the rarity of many gems, a matching set is disproportionately hard to find and will command a higher per carat price than if each of the gems from the suite were sold separately.

Gemstone Treatments

Skilfully merging art and science, a variety of techniques are used to help gemstones reach their full potential. Critical as good cutting, treatments are an integral part of the modern gemstone industry. With its roots in antiquity, most of the treatments used simply facilitate the beautiful end results of the earth’s natural processes. Click here to learn more.