Choosing a Colored Gemstone
I’m often asked about the various characteristics of the wide variety of colored gems by customers looking for the “perfect” gemstone. The choice of what gemstone might be right for you depends on a number of factors. In this brief article, I will try to outline some key considerations when selecting a gemstone. Hopefully it will be helpful to others as they embark on their personal journey to find that special gemstone.
Almost without exception the first thing on people’s minds when selecting a colored gemstone is obvious: Color! It is the most important consideration when selecting a colored gem. However, many do not realize both the wide variety of colors available, and the fact that many gem species come in a wide variety of natural colors. For example, sapphires can be found in nearly every hue of the rainbow, as demonstrated by the headline photo. Other gemstone species with a broad range of colors are garnets, spinel, zircon and tourmaline. That wide variety of color also presents challenges–it can be incredibly difficult to precisely match a specific color. If you have to have a certain shade or hue, it might severely limit your options in terms of gem species, cut or size. Finding matched pairs or sets can be even more difficult. Apparent color is a function of both the hue–where the color falls on a color wheel–and saturation, the intensity of the color. The final component of apparent color is tone–how light or dark a stone appears.
Unlike diamonds, there is no industry standard system for grading clarity in colored stones–and with good reason, as they are simply too variable for a “one size fits all” approach. Many colored stones are fairly common, and can be found in larger sizes with few or no inclusions. Others, like emeralds, are rarely large or clean. Sapphires, especially unheated ones, typically have tiny needle-like inclusions of rutile. The Gemological Institute of America (GIA) has created a broad system for rating inclusions in colored gemstones that takes this into consideration. Using their system, gems can be classifed into three broad categories:
- Type I: Type I gemstones are typically very clean when mined and can be expected to have no eye-visible inclusions. Most common gemstones are Type I, such as aquamarine, tanzanite, quartz, morganite, Kunzite, zircon (blue), green tourmaline and a few others.
- Type II: Type II gemstones are generally expected to have a few minor eye visible inclusions. Some of the most desirable and rare gemstones are Type II, such as ruby, sapphire and alexandrite. Other common Type II stones are amethyst, apatite, garnet, peridot, spinel, all tourmaline except green, pink/red and watermelon and zircon (all but blue).
- Type III: Type III gemstones almost always are found with eye-visible inclusions. There are just a few Type III gemstones, the most well-known being emerald. Other Type III stones are red beryl, rubellite tourmaline (red and pink) and watermelon tourmaline, sphalerite and sphene.
I prefer to use a broad approach to describing the inclusions in my gems. What ultimately matters is whether the inclusions are visible to the naked eye, and if so, how they impact the appearance of the gem. That means face-up appearance–how a gem will be mounted. Often an inclusion will be easily visible when the gem is upside down, but difficult or impossible to see face up. Unless you are planning on mounting the gem upside down, ignore the appearance from the bottom. I describe gems as either loupe clean, eye clean or visibly included. Each gem has a description that talks about the appearance of the inclusions.
Loupe clean means exactly that: When viewed with a 10x loupe, there are no inclusions visible in the gem. In most colored gemstones, especially Type II and Type III stones this level of clarity is very rare. Eye clean means that no inclusions are visible at a normal viewing distance–put the gem on the back of your hand and view it at arm’s length, like you would view it when set in a ring. Note that you might be able to just barely see an inclusion in a stone like this if you look very closely, but overall it won’t effect the visual appearance under normal wear/viewing conditions. Finally, if a stone has visual inclusions, I will describe them as accurately as possible. Always keep in mind that my photos are magnified macro images, so the view is very close to the view through a 10x loupe.
The topic of gemstone treatments is too lengthy to go into much detail about it here. I try to sell as few treated gems as possible, although some gems are almost always treated, such as blue zircons and almost all blue topaz. The only treatments I will accept on gems I sell are irradiation/heat–used for blue topaz and some kunzite; heat–used for sapphire and tourmaline and some amethyst and oiling for emeralds. The choice about whether a treated gem is acceptable or not is a very personal one, but rest assured that I clearly disclose all treatments so you can make the choice that matters to you.
This is a very important characteristic of any gemstone that can be overlooked when selecting a gem. While many people are aware of the Mohs scale of hardness, most do not know that it is non-linear. That means that a gem that is for example 6 on the Mohs scale is much less hard than one that is 7 on the scale. Hardness is a measure of the gem’s resistance to scratching, but its just one measure of how durable a gem is. The other measure is toughness–how resistant a gem is to cracking or chipping. Gems with well-defined cleavage planes are susceptible to cracking or chipping if they are bumped or banged.
When looking for an engagement ring or any other ring designed for daily wear, you should stick to gems that are very durable–they have high toughness and hardness. This is one of the reason diamonds are popular, but also why sapphire is considered an excellent alternative engagement ring gem as sapphire is very hard at 9 on the Mohs scale and has excellent toughness–there are no defined cleavage planes in sapphire. I recommend sticking with sapphire for daily wear rings, but if you are careful you can also go with spinel, some garnets and beryl. Keep in mind that most of these stones besides sapphire may experience some chipping and abrading during daily wear, requiring them to be repolished after a few years. Even sapphire may need to be repolished after a decade or two if you are not careful.
Softer and less durable stones are best suited for either pendants and earrings, or used for occasional wear rings. Some stones are so soft I never recommend their use in a ring–for example sphalerite, or apatite.
My presumption is that if you’ve made it to my website, you’re already interested in a finer cut than is typically found in colored gemstones. Cut makes a big difference in visual appearance, and can even change how dark or light a color can appear. Deeper cuts can make a lighter-colored gem appear to be more saturated, while a very bright cut or a shallow design can help lighten up a dark gem. Careful placement of inclusions can hide their appearance in the finished gemstone. I work to optimize all of my cuts for the individual gemstone in question. My goal when I study a rough uncut gemstone is to figure out how I can simultaneously optimize the color, brilliance and face-up appearance of the finished gem. For that reason, I don’t do custom commission work, as I can’t guarantee a certain size or color upon request.
Apart from those considerations, the choice of a cut is also a personal one–some prefer a round, others an oval and others prefer different shapes. Because the natural shape of the rough dictates the shape I will cut some shapes will be more or less common in certain gem species. For example, sapphire rough is typically shaped such that rounds or ovals are the ideal shape for the finished gem. Rectangles, squares and trillions are much less common in sapphire. Tourmaline crystals tend to be long and thin, making rectangles very common in that species. When hunting for your perfect shape and cut, be aware that in some gem species your favorite shape may be much harder to come by.