Blue Agate is a layered form of chalcedony quartz. It is known to occur in a wide variety of colors and interesting patterns, including many shades of light to dark blue. Some popular trade names used for blue agate include blue lace agate, Mohave blue agate and blue banded agate. Many agates today may have been dyed, but unlike many other gem types, the dyeing of agate does not normally affect its value. However, any such treatment should always be disclosed by gemstone traders. Agate has excellent hardness and durability, making it one of the most versatile blue gemstones today. Blue Aquamarine is a member of the beryl family and is colored by traces of iron. Its color can range from blue to bluish-green and is typically very subtle, especially when compared to more vivid and intensely colored blue gemstones such as blue topaz. Aquamarine is one of the few naturally blue untreated gemstones (although some darker stones may be heated) and it has excellent hardness and durability. It is also known to occur with rare cat's eye chatoyancy. Aquamarine is also the official modern March birthstone. Blue Apatite is composed of calcium phosphate, the same material that makes up our teeth and bones. Although it is a very common mineral, gem-quality materials are extremely rare. Apatite is the defining mineral for 5 on the Mohs scale and it is known to occur in a wide variety of colors including a 'Paraiba'-like blue-green. Apatite is normally untreated, but one variety known as 'moroxite', is routinely heated to enhance its color. Some rare apatite gemstones may exhibit cat's eye chatoyancy, known in the trade as cat's eye apatite. Blue Azurite is a rare gem-quality variety of copper ore. There are two basic copper carbonate minerals - azurite and malachite. Of the two, azurite is much rarer. Azurite has a very distinctive and vivid blue color often described as, 'azure blue', hence its name. Azure blue refers to the unique deep lapis-like color seen in fine quality azurite. Azurite may also be found mixed with malachite, forming attractive blue-green gemstones. Azurite druzy is also very popular for jewelry, and it is much more durable for wearing owed to the hardness of its matrix rock. Blue Benitoite is a rare mineral first discovered in California by James Couch in 1907. It is a fine blue barium titanium silicate. It is one of the rarest gemstones available today. Benitoite has a higher dispersion rating than diamond and is known to display impressive brilliance and fire. Though the mineral benitoite has been found in various locations around the world, gem-quality and facetable material has only been found in San Benito, California. Benitoite is the official state gemstone for California. Blue Chalcedony belongs to the quartz group of minerals. Technically, 'chalcedony' is the umbrella term for all cryptocrystalline quartz. It can occur in a wide range of different colors, sizes and patterns. In the gemstone trade however, the term 'chalcedony' is typically used only to refer to 'chalcedony in the narrow sense' or 'actual chalcedony', which is the solid colored, translucent light-white to bluish gemstone. It's been recently discovered that chalcedony quartz is actually a combination of quartz and a polymorph known as moganite. Chalcedony takes an excellent polish and high quality materials can exhibit a glowing attractive luster. Blue Chrysocolla is a gem-quality hydrous copper silicate. It appears similar to both azurite and malachite. Although chrysocolla is most famous for its vivid blue to cyan green color, it can also be found in a wide variety of unusual and unique combinations of blue and green. Chrysocolla is colored by copper and is often confused with turquoise because of its similar color and appearance. Identifying chrysocolla by composition can be extremely difficult since it lacks a definitive chemical composition. Any blue to green copper-bearing silicate that cannot be specifically identified as something else otherwise, can essentially, be identified as chrysocolla. Most gem labs will not confidently issue identification reports for chrysocolla for these reasons mentioned. Blue Diamond is the hardest known natural material on earth, rating 10 on the Mohs scale of mineral hardness. Its name comes from the Greek word 'adamas', meaning invincible. Diamond is composed of pure carbon, the same material that makes up graphite, a very common material used in the production of pencil lead and various other industries. Blue diamond is typically irradiated to obtain its color, though some very rare stones may be completely natural and untreated. Most blue diamond will exhibit a secondary greenish hue. Blue diamond is prized for its rarity, exceptional hardness, high refractive index and high dispersion rating - the ability to split white light into its component colors. Blue Sapphire is the best-known blue gemstone (though it also occurs in many other colors). Sapphire's blue color can range from light-blue to deep-blue. Since sapphire is a gem-quality form of corundum, it is incredibly hard and durable, with a hardness of 9 on the Mohs scale. It is also considered to be one of the most precious of all gems available today. Some blue sapphires are known to exhibit phenomenal characteristics such as asterism (star) or color shift abilities. Today, blue sapphire from Sri Lanka (Ceylon) is considered most desirable, but previously, finds from Kashmir and Mogok, Burma, were known to be the finest quality. Blue sapphire from Cambodia (Pailin) was also known to be of distinctive purity. Many even consider Pailin sapphire to be close in quality to Kashmir, Burmese and Sri Lankan (Ceylonese) sapphire. Sapphire can also be found with phenomenal traits, such as rare color change sapphire, as well as remarkable chatoyant star sapphire. Blue star sapphire is highly sought-after and especially valuable by collectors and jewelers alike. Sapphire is also one of September's birthstones.
Gem, commonly, a mineral or organic substance, cut and polished and used as an ornament. Gems also are used as seals (items of assurance) and as talismans (good-luck charms). For birthstones, see month. Properties of Gems The qualities sought in gems are beauty, rarity, and durability. The beauty of a gem depends primarily on its optical properties, which impart its luster, fire, and color; the durability depends on hardness and resistance to cleavage or fracture. The physical properties by which gems are distinguished from each other are form of the crystal, index of refraction of light, hardness, presence or absence of cleavage, type of fracture (conchoidal, even, or uneven) in stones without cleavage, specific gravity, color, streak (color of the powder as determined by rubbing it over white, unglazed porcelain), luster (appearance of the surface in reflected light—adamantine, vitreous, resinous, greasy, silky, or pearly), and transparency. Minor properties that serve to identify some stones are chatoyancy (changeable luster or color under undulating light), opalescence, asterism (starlike sparkling), play of color, fluorescence, phosphorescence, iridescence, and electrical properties. The unit of weight used for gemstones is the metric carat; one carat equals 200 mg. Gem Cutting Gems are generally cut to bring out their natural color and brilliancy and to remove flaws. In the cabochon cut, the upper surface of the stone is smoothed and rounded into a simple curve of any degree of convexity; the lower surface may be concave, convex, or flat. All the remaining cuts have flat facets. In the table cut, the facets of the natural octahedron of the diamond are ground to smoothness and polished; one facet, the table, is ground much larger than any other and made the top of the gem, while the opposite facet, the culet, is left quite small. The rose cut consists of a flat base and (usually) 24 triangular facets—resembling a cabochon with facets. The brilliant cut is scientifically designed to bring out the maximum brilliancy of the stone. The crown of a brilliant consists of a table and 32 smaller facets, of which 8 are quadrilaterals and 24 are triangles; the base, of a culet and 24 larger facets, of which 8 are quadrilaterals and 16 are triangles. The base and crown are separated by a girdle. The brilliant cut has certain proportions—in general, the depth of the crown is one third the depth of the stone and the width of the table one half the width of the stone. The trap, step, or emerald cut consists of a table and quadriangular facets above and below the girdle with parallel horizontal edges. Diamond cutting and the cutting of other precious stones are distinct trades. Diamond Cutting In diamond cutting the stone is first cleaved or sawed to remove excrescences (outcroppings) or to break it into smaller stones. Cleaving is accomplished by making a groove in the surface in the direction of the grain, inserting a steel knife, and striking the back of the knife a sharp blow. The next process was formerly bruting, i.e., roughly shaping two stones by rubbing them against one another. In modern practice the stones are sawed with a revolving wheel coated on its rim with diamond powder, then shaped by inserting a holder, or dop, containing one diamond into a turning lathe that revolves it against a stationary diamond. The cutting of the facets and the polishing are done by a revolving iron wheel charged with diamond dust. After the facets are cut, the diamonds are cleaned and are ready for sale. Other Gemstones The cutter of gemstones other than diamonds is known as a lapidary. Precious and semiprecious stones other than diamonds are cleaved or slit by a revolving diamond-dusted wheel, faceted by being pressed against a lap (a smoothing and polishing tool) charged with diamond dust or a carborundum wheel, and polished with a softer abrasive. Most (and in the case of some gems all) of the work of faceting is done with only the eye of the lapidary as guide. Types of Gemstones Precious and Semiprecious Gemstones The precious stones are diamond; some forms of corundum (ruby, sapphire, Oriental emerald, Oriental topaz, and Oriental amethyst); and emerald. The chief semiprecious stones are aquamarine, amethyst, topaz, garnet, tourmaline, spinel, peridot (see olivine), zircon (see zirconium), chrysoberyl, quartz, opal, turquoise, moonstone, and jade. The organic gems are pearl, amber, coral, and jet; of these, pearl is usually counted as a precious stone. Counterfeit Gemstones Artificial and imitation gems are of various kinds. Synthetic stones are made in the laboratory of the same chemical elements as natural stones. Among the synthetic gems produced commercially are rubies, sapphires, emeralds, and spinels. Diamonds of gem quality have also been manufactured. Color changes are produced in diamonds by exposing them to radioactive bombardment. Synthetic stones may sometimes be detected by the presence of air bubbles, which, when numerous, cause a cloudy appearance; by having curved rather than straight striae; and by their unnatural color. Doublets are made by combining a crown, or upper part, which is a thin slice of either the true stone or some inferior but hard gem, with a lower part of the true stone, a substitute stone, colored glass, or colored paste. Triplets generally consist of a layer of paste between two genuine stones of poor color. Paste (glass) gems usually contain lead and are consequently very soft; they soon lose their brilliance and color. Imitation pearls are glass or plastic beads coated with a preparation made from fish scales. A cultured pearl is made by inserting a small bead inside the oyster; the irritation causes the oyster to deposit pearly material upon the bead, leading to the formation of a pearl.
The idea that some gemstones are precious and others are only semi-precious is familiar to every buyer of colored stones. Precious stones - diamond, ruby, sapphire and emerald - traditionally command high prices due to their extraordinary color or brilliance and extreme rarity. While the precious stones are deservedly famous, the conventional distinction between precious and semi-precious gems is laden with myth and misconceptions. Let's try to sort out some of the myths from the reality. One common misconception is that the distinction between precious and semi-precious gemstones is traditional, going back many centuries. In fact it is a recent innovation, dating only to the nineteenth century. The first use of "semi-precious" to mean "of less commercial value than a precious stone" can be traced back to only 1858. Tsavorite Garnet Another misconception is that the list of four precious gems has a long history. In fact the traditional list of precious gemstones is rather longer and includes some surprising members. Pearl was considered to be precious; so was opal. One of the most traditional precious stones with a history going back to ancient Greece is amethyst. Amethyst was reclassified as semi-precious after large deposits were found in Brazil and Uruguay in the first half of the nineteenth century. The introduction of the term semi-precious into the English lexicon corresponds with the new amethyst discoveries. Of all the precious stones, diamond is the most subject to myth. It is interesting that the myths are of modern rather than ancient origin. Historically, colored gemstones such as ruby and sapphire were more highly valued than diamond, mainly because diamond was not particularly rare. But the twentieth century saw a major change. The first thing that happened is that very large finds in South Africa created an even more abundant supply of gem-quality diamond. At the same time, the perceived value of diamond has risen to the point where it's fair to say that diamond is at the top of the list of the precious stones in the mind of the buying public. What happened? Aren't precious gems valued particularly for their rarity? Rare Red Spinel In the 19th century, the collective worldwide production of diamond only amounted to a few pounds per year. After the discovery of the huge South African diamond mines in 1870, diamonds were being dug out of the ground literally by the ton. There was such a glut of supply and so little demand that the British financiers of the South African mines were in danger of losing their investment. Their solution was to create the powerful De Beers cartel that to this day controls worldwide diamond production and supply. Quality diamonds are actually not scarce at all. But De Beers controls how much supply comes on the market and that keeps prices high. The De Beers consortium also mounted a concerted advertising campaign that spanned decades, in order to create an association of diamonds with love, courtship and marriage, under the now familiar slogan "Diamonds are Forever". The diamond engagement ring, once unknown in most parts of the world (including Europe), is now considered an essential part of the ritual of marriage. It is hard to avoid the conclusion that diamond's special position as a precious stone is largely due to monopoly economics and social engineering. Natural African Tourmaline These days a number of rare semi-precious stones such as alexandrite, demantoid garnet, tsavorite garnet and tanzanite can be just as expensive as ruby and sapphire. Very fine tourmaline, spinel and large aquamarine gems also command very high prices. It is fair to say that we have now reached the point where the distinction between precious and semi-precious gemstones has become meaningless. The US Federal Trade Commission periodically considers banning the use of the terms altogether to reduce consumer confusion. Indeed, the American Gem Trade Association (AGTA) has already added the following text to their Code of Ethics; "Members should avoid the use of the term 'semi-precious' in describing gemstones".