Gemstone Library

The following gemstones are the more popular ones usually found in retail-stores. The text was compiled from the highly recommended “Jewelry & Gems – The Buying Guide” by Antoinette L. Matlins & A.C. Bonnano; you may purchase a copy from Gemlab Books and Instruments.


amethA transparent purple variety of quartz,is one of the most popular of colour gems. The birthstone of February, it was once believed to prevent the wearer from getting drunk, and if the circle of the sun or moon was engraved thereon, it was believed to prevent death from poison. Available in shades from light to dark purple, it is relatively hard, fairly brilliant, and overall a good, versatile, wearable stone, available in good supply even in very large sizes (although large sizes with deep colour are now becoming scarce). Amethyst is probably one of the most beautiful stones available at a moderate price, although one must be careful because “fine” amethyst is being produced synthetically today. It frequently exhibits colour zoning (often looking like chevrons). Amethyst may fade from heat and strong sunshine.


aquaA universal symbol of youth, hope, and health, blesses those born in March. (Prior to the fifteenth century it was thought to be the birth stone for those born in October.) Aquamarine is a member of the important beryl family, which includes emerald, but aquamarine is less brittle and more durable than emerald. Aquamarine ranges in colour from light blue to bluish green to deep blue, which is the most valuable and desirable colour. It is a very wearable gem, clear and brilliant, and, unlike emerald, is available with excellent clarity even in very large sizes, although these are becoming scarce today. One must be careful not to mistake blue topaz for aquamarine. While topaz is an equally beautiful gem, it is usually much less ex pensive since it is usually treated to obtain its desirable colour. For those who can’t afford an aquamarine, however, blue topaz is an excellent alternative – as long as it is properly represented … and priced. Also, note that many aquamarine-colored synthetic spinels are erroneously sold as aquamarine.


citrOften called quartz topaz, citrine topaz, or topaz, all of which are misleading. It is yellow, amber, to amber brown. While a pleasing stone in terms of colour, and fairly durable, citrine is slightly softer and has less brilliance than precious topaz. It also lacks the subtle colour shading, the pinkier yellow or pinkish amber shades, which lend to precious topaz a distinctive colour difference. (Much citrine is made by heat-treating purple amethyst.) Citrine is also much less expensive than precious topaz. It should never be represented as topaz, which technically is “precious” or “imperial” topaz. Citrine is plentiful in all sizes, and can be made into striking jewellery, especially in very large sizes, for a relatively small investment.


emerThe green variety of the mineral beryl and one of the most highly prized of all the gems. Aside from being the birthstone for May, it was historically believed to bestow on its wearer faithful ness and unchanging love, and was thought to enable the wearer to forecast events. The finest-quality emerald has the colour of fresh young green grass an almost pure spectral green, possibly with a very faint tint of blue, as in the “drop of oil” emerald from Colombia, which is considered to be the world’s finest. Although a hard stone, emerald will chip easily since it tends to be somewhat brittle, so special care should be given in wearing and handling. Because of emerald’s popularity and value, imitations are abundant. Glass (manufactured complete with “flaws”), doublets or triplets such as “aquamarine emeralds” and “Tecla emeralds,” which are clever imitations made by inserting layers of green glass (or, more frequently, a green cementing agent) between pieces of aquamarine or quartz “crystal” are often encountered. Also, fine synthetic emeralds have been produced for many years with nearly the same physical and optical properties (colour, hardness, brilliance) as genuine emerald. Techniques to enhance colour and reduce the visibility of flaws are also frequently used. A common practice is to boil the emerald in oil (sometimes tinted green), a practice that goes back to early Greek times. This is a widely accepted trade practice, since it is actually good for the stone in light of its fragile nature. Oiling hides some of the whitish flaws, which are actually cracks, filling the cracks so they be come less visible. The oil becomes an integral part of the emerald un less it is subjected to some type of degreasing procedure. The development and use of the ultrasonic cleaner has brought to light the extensiveness of this practice. Never clean emeralds in an ultrasonic cleaner.


garnet Belongs to one of the most exciting families in the gem world. A hard, durable, often very brilliant stone, available in many colours (greens, reds, yellows, oranges), it offers far greater versatility and opportunity for the jewellery trade than has yet been capitalised upon. Depending upon the variety, quality, and size, lovely garnets are available for under $20 per carat or more than $3,000 per carat. Garnet also occurs in certain shades of red that have been taken for some varieties of ruby. And in yellow it has been confused with precious topaz. Garnet can be found in almost every colour and shade except blue. It is best known in a deep red variety, sometimes with a brownish cast, but it is commonly found in orangish brown shades, and brilliant wine red shades as well. Other colours include orange, red purple, violet, and pink.


opal Whose brilliance and vibrant colours resemble the colours of the fall, is certainly appropriate as a birthstone for October. When we try to describe the opal, we realise how insufficient the English language is. It is unique among the gems, displaying an array of very brilliant miniature rainbow effects, all mixed up together. Its most outstanding characteristic is this unusual, intense display of many colours flashing out like mini-rainbows. This effect is created by opal’s formation process, which is very different from that of other gems. Opal is composed of hydrated silica spheres. The mini rainbows seen in most opals result from light interference created by these spheres. The arrangement of the spheres, which vary in size and pattern, is responsible for the different colours seen. Opal is usually cut flat or in cabochon, since there is no additional brilliance to be captured by a good faceting job. Colour is everything. The more brilliant the colour, the more valuable the gem. It is probably truer of opal than any other stone that the more beautiful the stone and its colour, the more it will cost.


peridotThe birthstone for August. Peridot was also a favourite of the ancients. This lovely transparent yellowish green to deep chartreuse stone was quite a powerful gem. It was considered an aid to friendship and was also believed to free the mind of envious thoughts. (Which is probably why it was an aid to friendship.) Because of its yellowish green colour, it was also believed to cure or prevent diseases of the liver and dropsy. And, if that’s not enough, if worn on the left arm it would protect the wearer from the evil eye. It is also popular today, but probably more for its depth of green colour than its professed powers. While not particularly brilliant, the richness of its colour is exceptional. It comes in shades of yellowish green to darker, purer green colours. It is available in small sizes; larger sizes are becoming scarce. It is not a hard stone and may scratch easily. Also, some stones may look like peridot (green sapphire, green troumaline) and be mistaken for peridot and be misrepresented.


ruby Birthstone for July. Ruby is the red variety of the mineral corundum. Historically, it has been symbolic of love and passion, considered to be an aid to firm friendship, and believed to ensure beauty. Its colour ranges from purplish or bluish red to a yellowish red. The finest colour is a vivid, almost pure spectral red with a very faint undertone of blue, as seen in Burmese rubies, which are considered the finest. The ruby is a very brilliant stone and is also a very hard, durable, and wearable stone (a hardness of 9 on Mohs’ scale). Because of these characteristics, ruby makes an unusually fine choice for any piece of jewellery. As it is true for other popular gems – the greater the value and demand, the greater the use of techniques to “improve” or to simulate. Again, examples of almost every type of technique can be found: colour enhancement, synthesis, substitutes, doublets, triplets, misleading names, etc. The newest synthetic rubies – the Kashan ruby and Chatham ruby – are so close to natural ruby in every aspect that many are actually passing for genuine. When getting a very fine, valuable ruby certified, make every effort to select a gemmologist with both many years’ experience in coloured gems and an astute knowledge of the marketplace today.


sapphBirthstone of September. The finest sapphires are considered to be the blue variety – specifically those from Burma and Kashmir, which are closest to the pure spectral blue. Fine, brilliant, deep blue Burmese sapphires will surely dazzle the eye and the pocketbook, as will the Kashmir, which is a fine velvety-toned deep blue. Many today tend to be too dark, how ever, because of the presence of too much black and poor cutting (cutting deep for additional weight), but the deep blues can be treated to lighten the colour. The Ceylon sapphires are a very pleasing shade of blue, but are a less deep shade than the Burmese or Kashmir, often on the pastel side. We are also seeing many Australian sapphires. These are often a dark blue, but have a slightly green undertone, as do those from Thailand, and sell for much less per carat. They offer a very afford able alternative to the Burmese, Kashmir, or Ceylon, and can still be very pleasing in their colour. Blue sapphires also come from Tanzania, Brazil, Africa, and even the U.S.A. (Montana and North Carolina). They also come in other colours, especially yellow and pink, and in smaller sizes some beautiful shades of green. These are known as fancy sapphires. Compared to the cost of blue sapphire and ruby, these stones offer excellent value and real beauty. Techniques have been developed to treat natural sapphires to remove a certain type of flaw (needle type) and to change the colour for example, to create a “Ceylon” sapphire that never came from Ceylon (Sri Lanka) but whose colour looks like that of a Ceylon.


tanzA variety of the mineral zoisite was not considered a gem material until 1967, when a beautiful, rich, blue to purple blue, transparent variety was found in Tanzania (hence tanzanite). Tanzanite can possess a rich, sapphire blue colour (possibly with some violet red or greenish yellow flashes). This lovely gem can cost over $2,000 per carat today in larger sizes. But one must be cautious. It is relatively soft, so we do not recommend tanzanite for rings (unless it’s set in a very protected setting) or for everyday wear in which it would be exposed to knocks and other abuse. One must also be aware that a very inexpensive, dull, brownish zoisite can become a beautiful, expensive tanzanite after heat treatment.


topaz A symbol of love and affection is the birthstone for November. It is one of nature’s most wonderful and least-known families. The true topaz is rarely seen in jewellery stores. Unfortunately, most people know only the quartz (citrine) topaz, or glass. In the past almost any yellow stone was called topaz. True topaz is very beautiful and versatile. Topaz occurs not only in the transparent yellow, yellow brown, orangy brown, and pinky brown colours most popularly associated with it, but also in a very light to medium red (now found naturally in fair supply, although many are produced through heat treatment), very light to light blue (also often the result of treatment, although it does occur naturally on a fairly wide scale), very light green, light greenish yellow, violet, and colourless. Topaz is a hard, brilliant stone with a fine colour range, but it is much rarer and much more expensive than the stones commonly sold as topaz. There are many misleading names to suggest that a stone is topaz when it is not, for example, “Rio topaz,” “Madeira topaz,” “Spanish topaz,” and “Palmeira topaz.” They are types of citrine (quartz) and should be represented as such. Blue topaz has become very popular in recent years; most of it treated (there is no way yet to determine which have been treated and which are natural). It closely resembles the finest aquamarine (which is very expensive today) and offers a very attractive, and much more affordable alternative.


turm A gem of modern times, but nonetheless has found its way to the list of birthstones, becoming an “alternate birthstone” for October. Perhaps this honor results from tourmaline’s versatility and broad color range. Or perhaps to the fact that red-and-green tourmaline, in which the red and green occur side by side in the same stone, is reminiscent of the turning of October leaves. Whatever the case, tourmaline is one of the most versatile of the gem families. It is available in every color, in every tone, from deep to pastel and even with two or more colors appearing in the same stone, side by side. There are bicolored tourmalines (half red and the other half green, for example) and tricolored (one-third blue, one-third green, and one-third yet another color). The fascinating “watermelon” tourmaline looks just like the inside of a watermelon-red in the center surrounded by a green “rind.” Tourmaline is a fairly hard,durable, brilliant, and very wearable stone with a wide choice of colours.


tsavo A member of the garnet family and is often mistaken for other (usually more expensive) gems. It is one of the most beautiful, and all but a few would assume it was an emerald of the finest quality. In fact, it is “clearer,” more brilliant, and more durable. There is also a rarer green garnet, called demantoid, which costs slightly more than tsavorite but which, although slightly softer, has more fire. These gems offer fine alternatives to the person desiring a lovely green gem who can’t afford emerald. While still rare, expensive gems themselves, they are far less expensive than an emerald of comparable quality.


Visit also the following pages in GEMOLOGY WORLD:

Visit to a topaz mine in Brazil: Video (1.05 minutes)