Choosing a Colored Gemstone

We’re 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.

Color

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. Other gemstone species with a broad range of colors are garnets, spinel, zircon and tourmaline.  

Clarity/Inclusions

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.

Some colored stones are prolific and can be easily found in larger sizes with few or no inclusions.  Other colored stones, like emeralds, are rarely large or clean. Sapphires nearly always have tiny needle-like inclusions of the mineral rutile, though their appearance is commonly improved with heat treatment.

The Gemological Institute of America (GIA) has taken this into consideration when creating their system for classifying the expected inclusions in colored gemstones; it’s used in their gemological training, but it is not used on reports. Using their system, gems can be classified 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, blue zircon, 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 all but blue zircon.
• 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 and watermelon tourmaline, sphalerite, and sphene.

Although GIA uses this system in its training, it is not used on reports. In fact, there is no data on clarity included in colored stone reports. What ultimately matters is whether the inclusions are visible to the naked eye, and if so, how they impact the appearance of the gem once 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, it’s best to ignore the appearance from the bottom. We describe gems as either loupe clean, eye clean or visibly included.  

We always include a description of the inclusions for every gem on our website. Keep in mind that all of our photos are taken with a professional high-resolution camera and uploaded to the website in high resolution. Consequently, the photos will show details not visible to the unaided eye. Learn more about gem clarity here.

Treatments

The topic of gemstone treatments is a complex one. We 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.

We only accept a small set of widely recognized treatments for the gems we offer:

• Irradiation and heat, used for blue topaz and some kunzite
• Heat treatment, commonly used for sapphire, tourmaline, and occasionally amethyst
• Oil treatment, traditionally used to enhance emeralds

Whether or not a treated gemstone is right for you is a personal decision—and one we fully respect. That’s why we clearly disclose all treatments, so you can make the choice that feels right to you.

Hardness/Durability

Hardness refers to a gem’s resistance to scratching and is measured using the Mohs scale. However, the Mohs scale is non-linear, meaning the difference between each number is not equal. For example, a gem rated 7 is much harder than a gem rated 6.

Another important factor is a gem’s toughness, or it’s resistance 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, or rank high in both toughness and hardness. This is why sapphire is considered an excellent alternative engagement ring gem, ranking a 9 on the Mohs scale. Sapphires have excellent toughness since they do not have defined cleavage planes.

We recommend sticking with sapphire for daily wear rings, but if you are careful, you can also choose a spinel, some garnets, or 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.  

Softer and less durable stones are best suited for either pendants and earrings, or used for occasional wear rings.  

The Quality of a Gem’s Cut

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. We work to optimize all cuts for the individual gemstone in question. Our goal when we study a rough uncut gemstone is to figure out how we can simultaneously optimize the color, brilliance and face-up appearance of the finished gem. For that reason, we don’t do custom commission work, as we 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 we 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.