How to Buy a Colored Gemstone
Beyond their beauty, colored gemstones have deep meaning. Each one is linked to symbols of personal and spiritual destiny. Taken together, the stones are said to influence health, love, peace, strength, success, and wisdom, as well as fortune-telling and psychic powers.
Natural Colored Gemstones
Natural colored gemstones come from the earth, where combinations of heat, pressure, water, chemistry, and time create unique mineral deposits. Most colored gemstones are born in the earth’s top-most layer or “crust.” Peridots (like diamonds) are an exception, coming from the mantle, below.
Once formed, colored gemstones can be embedded in solid rock or moved by wind or water to more accessible secondary locations, like streambeds, and scattered in smaller pieces. Depending on the setting, the stones are recovered by machine or by hand and then, typically, cut and polished.
Colored gemstones are created all over the world, except Antarctica. While many types of stones can be found in multiple locations, others are more limited. Sapphires, for example, come from sites ranging from Madagascar to Montana. But, tanzanites are from a single, remote spot in Africa.
For any stone, the term “natural” refers to its original creation. It is quite common — sometimes essential — for a stone’s appearance (i.e. color or clarity) to be enhanced after the fact, by one or more sophisticated treatments. Untreated stones are actually quite rare.
Lab-Grown Colored Gemstones
Lab-grown (or synthetic) colored gemstones are created by science, rather than nature. They have essentially the same chemical, physical, and optical properties as natural stones, and may have fewer inclusions. But they are, typically, less prized than their natural counterparts.
In gemological terms, types of colored gemstones — such as emeralds, rubies, or sapphires — are called varieties. There are many varieties, and each one contains stones with specific, similar traits. Among other things, these can include chemical, mineral, and structural features, as well as aspects of durability, density, and light separation. These aspects are more formally known as hardness (on the Mohs Scale), specific gravity, and refractive index.
Emeralds, for example, are hexagonal structures made of beryl, or beryllium aluminum silicate. They are rated 7.5–8 on the Mohs Scale, with a specific gravity of 2.67–2.78 and a refractive index of about 1.577–1.583. Emeralds are green, courtesy of chromium, and sometimes, vanadium.
Rubies, on the other hand, are hexagonal crystal structures made of corundum, or aluminum oxide. They are harder and denser than emeralds (9 on Mohs, with a specific gravity of about 4.0). And they have a refractive index of approximately 1.762–1.770. Rubies are red in color, due to the presence of chromium.
Sapphires are also made of corundum and share the hardness, density, and refractive index of rubies. However, depending on trace mineral content, sapphires can exist in virtually any color.
Many other colored gemstone varieties also come in a surprising range of hues. Some of the most famous are diagramed below:
Colored gemstone jewelry is as varied as the stones themselves: rings, earrings, pendants, necklaces, bracelets, and brooches in a wide range of metals and settings.
Colored gemstone jewelry is typically described with measurements, in millimeters (versus carat weight, as for diamonds). This standard creates more of an “apples to apples” comparison between different stone varieties and densities. And it provides a good sense of a stone’s size, when viewed from the top.
Many popular colored gemstones have the added distinction of being birthstones. According to the American Gem Society, the US list (with diamonds and pearls) includes:
PEARL ALEXANDRITE MOONSTONE
TANZANITE ZIRCON TURQUOISE
Colored gemstones offer a virtual kaleidoscope of shopping options. Their variety — in hue, shape, size, symbolism, and pricing — can be spectacular. And, it can set the stage for a truly personalized purchase.
The beauty of a stone is, ultimately, in the eye of the beholder. Still, some basic quality measures can provide perspective. A gemological report from a trusted, independent laboratory, like EGL ASIA, can provide key information like color, cut, and transparency, as well as confirmation of a stone’s type, treatments applied to enhance its appearance, and its environmental friendliness. Taken together, these aspects can greatly impact a colored gemstone’s visual impression and value.
Important quality-related colored gemstone terms include:
Colored gemstones are usually measured by carat weight. One carat (ct.) equals 1/5 of a gram. It’s important to note that density can vary between gemstone types. A sapphire, for example, is denser than an emerald. So, a sapphire will actually be smaller than an emerald of comparable cut and weight. In the end, the perceived size of any colored gemstone will depend not only on its weight, but also on factors such as its shape, style, and setting.
Colored gemstones are known for their breathtaking colors — or, in scientific terms, their combinations of hue (primary color impression), tone (lightness), and saturation (strength). While color choice is entirely personal, pure, rich colors with medium tone are, typically, the most prized.
Color can be completely natural, man-made, or a bit of both. Typically, colored gemstones have single shades. But, more unique phenomena can create dazzling and distinctive effects: multiple colors, color changes, or visual patterns and shapes within the stone. A simple tilt of the hand can create true magic, bringing the beauty of the gem to a whole new level.
Cut (Shape and Style)
Cut describes the silhouette of a colored gemstone — a combination of shape and, often, style, as shown below. Different stone types may favor particular cuts. However, beautiful stones can be found in virtually any shape or style.
Top (Crown) View Side (Pavilion) View
Colored gemstones come in a wide variety of sizes; choosing one is purely a matter of preference. However, natural emeralds, rubies, and sapphires of fine quality tend to be especially scarce in larger sizes. So, other factors being equal, they can be the most costly. The dimensions of a round colored gemstone are expressed as maximum-minimum diameter x depth, in millimeters. Fancy shapes are indicated by length x width x depth.
The appeal of a colored gemstone is greatly influenced by the amount of light it transmits. Texture and the presence (or absence) of internal features play a key role in determining whether a stone is transparent (preferred for most colored gemstones) or something less so, such as translucent or opaque.
Note: All photos and diagrams above are intended as general guides.
Renderings may vary with computer settings.
Among the world’s many famous colored gemstones, these are particularly notable for their large scale, brilliant colors, and mesmerizing displays of light:
The 563-carat Star of India is the world’s largest gem-quality blue star sapphire. The enormous milky, blue-gray stone, uniquely, has a star pattern on two sides. In 1964, it was notoriously stolen from the American Museum of Natural History. Later retrieved in a locker at a Miami bus depot, it is on display at the same museum today.
The Logan Sapphire is a 423-carat faceted violet-blue stone from Sri Lanka. Known for its exceptional clarity, the Logan Sapphire is set in a silver and gold brooch with 20 round, brilliant-cut diamonds and is housed at the Smithsonian.
The MacKay Emerald is a 167.97-carat emerald set in an art deco-style pendant with 35 emeralds and 2,191 colorless diamonds. The 75.47-carat Hooker Emerald is a beveled, square-cut stone mounted in a platinum brooch with 129 diamonds. Both emeralds were mined in Columbia and are currently displayed at the Smithsonian.
One of the largest star rubies in the world is the Rosser Reeves Star Ruby. Rich red in color and 138.72 carats in weight, the ruby is from Sri Lanka. It also lives at the Smithsonian.
The care required for colored gemstones varies with each beautiful piece. Safekeeping begins with their wearing: Always put them on last and take them off first. Avoid all chemicals and cosmetics (including perfume and hair spray); intense exposure to heat, light, or quick temperature changes; and any physical activities that may damage the stones. When not in use, colored gemstones should be stored separately, in a soft pouch.
The safest way to clean any colored gemstone is with a soft, slightly moistened cloth. Stronger methods may be acceptable for certain stones, depending on what they are and how/if they have been set or enhanced. But, these approaches should only be considered with care and in consultation with a professional jeweler. A jeweler should also check each gemstone mounting on a regular basis.