A Few Notes About Gemstones and Color

The subject of color in gemstones is a highly-complex specialty in itself. Our purpose here is only to present a few notes about color in some of the best-known colored gemstones. Also, we have included a few comments about some cases where the color of a gemstone helps to define what "type" of stone it is, and a couple of gemstone myths.

It is important to remember that on this page we are dealing primarily with common names and attributes of gemstones. In many cases, the species and varieties discussed have scientific and/or accepted industry names which are not well-known to the public-at-large.

Color, Light, & Heat: For many gemstones, the color is considered "stable". This means that when exposed to light or normal heat, the color won't fade or change. For many other gemstones, the color is considered "unstable". This means that there are circumstances of what are considered to be normal heat and/or light which will cause the stone to fade, or the color to alter in some other way. For example, all colors of sapphire are considered to be stable. In general, you can wear them in the heart of the  desert without wondering if they will fade from the sunlight or heat. On the other hand, kunzite and brown topaz will fade rapidly when exposed to light -- even bright indoor light (some brown topaz has been shown to lose color between the mining site and the mine entrance). They should be worn in the evening, and stored in a dark place when they aren't being worn. When you purchase a gemstone, be sure you find out from a reputable source about the light and heat sensitivity of the stone. Also remember that most jewelry store salespeople are just salespeople -- they are neither jewelers nor gemologists.

Heat is often used to enhance the color of gemstones, and generally requires several hours of soaking at very high temperatures, followed by careful cooling, to achieve the desired color. Again using the example of sapphire, most sapphires (and rubies) on the market today are heat treated to enhance their color. Contrarily, heat is also used to remove color from sapphire. Most "white" sapphire on the market is heat treated to remove all traces of natural color. Many other gemstones are also heat-treated to either remove or enhance color. 

In some cases, heat can be used to change the color of a gemstone. The best example of this is amethyst, which when heated turns to the yellow of citrine. Most of the citrine on today's market started out as amethyst. This is also the case with ametrine. Ametrine was originally found in a single mine in Bolivia. Now, it is produced from amethyst using carefully-controlled partial heating of the stone. While heating is less of a risk to the consumer than light, heat can also damage your gemstone, either through color change or by cracking from stresses induced by the heat. So, when you're fixing that holiday meal, protect your gemstones -- take them off or otherwise protect them from the heat. This even applies to diamonds, even though they are frequently considered to be indestructible -- they aren't, even though they are harder than all other gemstones. In the same vein, many household chemicals can damage gemstones -- they should never be worn when using these products.

It is common for followers of crystal lore to place some types of crystals in the sun to recharge their mystical properties. First, extensive exposure to bright light -- especially sunlight -- will cause any colored gemstone to fade. Second, a crystal should be intact, or nearly so, to have these mystical properties. By definition, a cut gemstone is no longer a mystical crystal, so there is no reason to "soak" one in the sun. We had a customer do this with a very nice ruby heart -- it is now a fair quality light pink sapphire after being "soaked" in the summer Southern California sun for several weeks. If you still feel that you would like to expose a gemstone to sunlight to recharge any mystical properties, a few minutes total exposure over a lifetime is more than enough.

The "Quality" of Color: Arguably, the two most important components of "quality" in gemstone color are hue and saturation.

Hue is what we mean when we talk about gemstone color. The general hue of amethyst is purple, whether it is the lightest of lilacs or the deepest royal purple. Similarly, the specific hue of London-Blue Topaz is deep very-slightly-greenish blue. 

Saturation is, perhaps oversimplified, how much color a stone has. Using amethyst again, Rose de France is very-lightly-saturated amethyst: it is usually a light slightly-pinkish-lilac hue. Pau D'Arco is a very deep red-purple hue. 

An important note about saturation is that we use both deep and dark to describe highly-saturated hues. Deep is a desirable characteristic, because the stone has a very rich hue, and is also still transparent. Even though it may be difficult to see through, it is still possible. Dark, on the other hand, is generally undesirable. While the saturation is typically excellent, the stones are opaque. This is what is frequently sold on the TV shopping channels as top-grade sapphire (sometimes referred to as "midnight" sapphire). It is actually one of the absolutely lowest gemstone grades, because it is opaque. (Opaque stones have their place, but our topic here is transparent gemstones.) Another way to think of them is that deep means a lot of color, and light can get through. Dark means a lot of color, and light can't get through, or only gets through very weakly.

What's in a Name?: Frequently, a gemstone is defined by it's color. For example, there are several different varieties of beryl, but only aquamarines are blue. Similarly, emeralds are green. Pink beryls are morganite, and there are several other colors which define unique varieties, all of which are beryl. The difference is the presence (or absence) of different impurities. 

There are many other cases where we refer to gemstones by a descriptive name plus the name of the species. For example, most tourmaline is defined by color, such as pink tourmaline, or the location where a variety was first discovered, such as Paraíba tourmaline. To help confuse things, deep red tourmaline has its own name -- rubellite, which means "like ruby". Also, a slice across the most common form of natural tourmaline crystal is called "watermelon tourmaline", because it has a green rim around a red core, just like watermelon. 

This naming convention is also typical of corundum: When it's red, the name is ruby; all other colors are sapphire, defined only by their color or sometimes by their place of origin (or even both!). All Kashmir Sapphire is blue, but not all sapphires from Kashmir are blue. The first example is a specific name based on where a particular color was found, the second is just a location for finding sapphires. Another example is Montana sapphire. These sapphires all come from Montana, but they run the gamut of colors. Many Montana sapphires are pastel, or lightly-saturated, but some are quite deep and exceptionally attractive, such as the Yogo sapphire, found only in Yogo Gulch, Montana.

In several types of gemstone, especially the beryls, many marketers have started referring to distinct varieties as a different color of a better-known -- and sometimes more-valuable -- gemstone. For example, it is sadly common to come across bixbite being called "red emerald". Another recent example is "green amethyst", which is actually prase or prasiolite. This is not only ethically questionable, it is a violation of US Fair Trade rules. You should steer clear of anyone taking such liberties, at least in regard to that particular stone.

This page is under continuing development....

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