PERIDOT

The beautiful colors of these brilliant zircons are the result of heat treatment given to natural, reddish brown stream pebbles. The three stones at the left (from top) weigh 118, 103, and 98 carats, and the ones on the right weigh 106 and 29 carats. The 106-carat stone came from Thailand, the others from Indochina. (Four-fifths actual size.)

In addition to being reddish brown, natural zircon may vary from almost colorless to yellow, red, orange, and brown or from yellow-green to dark green and, occasionally, blue.

The most important producing areas of gem zircon are in a region of Indochina that comprises parts of Thailand, Viet Nam, and Laos. Additional gem zircon, like so many of the other gem species, is recovered from near Moguk in Upper Burma and from the gem gravels of Ceylon.

There is no synthetic zircon on the market, but a bright blue synthetic spinel is sometimes used to simulate zircon successfully.

The relative rarity of peridot and the ease with which it can be simulated in glass, whose luster it approximates, probably account for the low popular demand for this gemstone. Although peridot has little brilliance and no fire, its unusual color and glassy luster produce a unique effect that serves to make it attractive.

The color of peridot is an unusual bottle green that shades, in some stones, toward yellow-green and, more rarely, toward brown. In 1952 it was discovered that almost all of the brown gems believed to have been peridot in various gem collections were actually of an entirely unrelated species, which since has been named sinhalite. Brown peridot still remains rare and is somewhat of a collector’s item.

To exhibit its unique color to best advantage, peridot usually is cut so as to have a relatively large table, as shown in these examples. The largest gem, weighing 310 carats, is from the Egyptian island of Zebirget in the Red Sea and is the largest cut peridot known. The other two, weighing 287 carats and 109 carats, are from Burma. (Three-fifths actual size.)

The green of peridot, which is quite different from the green of other gemstones, is due to some iron included in its composition. It is suspected that atrace of nickel contributes to the liveliness of the color.

This photo shows the color of peridot projected onto the background. The larger gem is the 310-carat stone shown in the prior illustration. The stone on the right weighs 109 carats and is from Burma; the other peridot weighs 46 carats and is from Egypt. (Almost actual size.)

Peridot has a hardness of only 6½ and a rather strong tendency to cleave, and these characteristics reduce its value for use in jewelry exposed to rough wear. It is better used in pins, earrings, and pendants than in rings.

Peridot is a gem name for the common mineral olivine, a magnesium silicate. Olivine is fund in numerous places, and small gemmy pieces are found in many localities. Many of the largest and best gems of peridot have come from mines on the Egyptian island of Zebirget (Island of St. John) in the Red Sea, but most gem peridot now comes from Burma. Great numbers of small stones have been cut from olivine found in Arizona gravels.

Centuries ago, peridot was known by the name topaz, since the stones came from Topazos, the island now known as Zebirget. The name topaz, as we have seen, is used today for an entirely different mineral species.

Spodumene, a lithium aluminum silicate, is one of the very few gemstones containing lithium. It has had more importance as a gemstone in the United States than elsewhere, a situation due to early discoveries of unique occurrences of a lavender-pink variety at Branchville, Conn., in 1879 and in San Diego County, Calif, about 20 years later. At the time of the discovery of the California material, the variety was namedkunzitein honor of G. F. Kunz, a noted American gemologist of the times.

The 177-carat kunzite (at lower left) is a large flawless stone cut from California material of this variety of spodumene. It was given to the Smithsonian Institution by the American Gem Society. The other stones, all from Brazil, represent the more usual shades of spodumene. They weigh 327 carats (top left), 256 carats (top right), and 69 carats. (About half actual size.)

The finding of a bright green variety,hiddenite, in North Carolina about 1880 greatly stimulated the interest of American gem collectors. Some of the bright green spodumenecoming from Brazil in recent years compares very favorably in color with North Carolina hiddenite. Other than in a scattered few of these unusual occurrences of kunzite and hiddenite, spodumene usually is found in yellow and yellow-green shades, with Brazil and Madagascar being the chief sources.

This 880-carat kunzite from Brazil is one of the largest stones of its kind. (About actual size.)

Spodumene has a hardness of about 7, but with a refractive index of about 1.66 and a low dispersion there seems to be relatively little to recommend it as a gemstone. The fact that it exhibits a very strong tendency to cleave in two different directions would seem to rule it out completely as being too difficult to cut. Nevertheless, the production and purchase of cut stones of spodumene persist because of the beauty of the gem.

The kunzite and hiddenite varieties of spodumene show strongpleochroism, or the ability to show three different colors when viewed in the direction of different axes. Some of the large Brazilian kunzite crystals mined in the early 1960’s havean intense rose-violet color when viewed along the long axis of the crystal but have pale blue-violet and pale tan colors when viewed from the other two directions. When heat treated, or exposed to strong light, this Brazilian kunzite loses its tan and bluish colors but retains the intense rose-violet. Because of spodumene’s pleochroism, the direction of cutting in the stones becomes extremely important, as it must be done in a manner that will take advantage of the violet color in kunzite and the green color in hiddenite.

The name garnet is applied to a group of six closely related silicate minerals that are alike in crystal structure but that differ mainly in the substitution of certain metallic elements in their composition. These minerals are:

Most natural garnets have compositions intermediate between members of the basic group of six. For example, there are garnets having compositions anywhere between pyrope and almandine, depending on the amount of difference in the magnesium or iron content. These same garnets may even have varying amounts of manganese, and thus be partially spessartine.

The six garnets in the basic group are found in considerable quantity in many areas, but seldom are they of sufficiently high quality to be considered gemstone material. Even when stones of gem quality are found, their colors—particularly the reds—tend to be so intense that they seem to be opaque.

Garnets occur in several colors, although most people think of them as red. Shown here are a 54-carat spessartine from Brazil (top right), a 6-carat rhodolite from North Carolina (at left), a magnificent 10-carat green demantoid from Russia, a 9-carat grossular from Ceylon (bottom), and a 26-carat spessartine from Virginia. (Seven-eighths actual size.)

Garnet has a hardness (about 7) suitable for gemstone material and a fairly high refractive index (1.74 and above).

Ruby red pyrope is the most popular variety of garnet. It is found in Bohemia, in Czechoslovakia, where it occurs as small, poorly shaped crystals. Red pyrope also is found in Africa, where it is called Cape ruby, and in Arizona, where it is sold as Arizona ruby. Another kind of pyrope calledrhodoliteis noted for its soft, rosy purple color. Actually, rhodolite is one of the intermixed garnets with a composition somewhere between pyrope and almandine. Most of the fine rhodolite gems have come from North Carolina.

Almandine is popular in its deep red, transparent form, but since the red is so dark and intense that it appears black, the stones usually are cut as cabochons with the back hollowed out. This makes them thinner, and thus lightens their color. Garnets cut in this manner are all known as carbuncles.Brazil, India, Ceylon, Australia, and parts of the United States are important sources of almandine.

Although spessartine has a rich orange color, it is not often used as a gemstone because of the relative rarity of gem-quality cutting material. This mineral gets its name from the town of Spessart, Germany, where it was first found. Excellent spessartine with colors ranging from orange to brown has been found at Amelia Court House, Va., and quality gems have been cut from such material. Ceylon, Burma, Madagascar, and Brazil also have furnished some gem spessartine.

The chromium garnet, uvarovite, generally is too poor in quality for cutting. Uvarovite crystals, which are emerald green in color, occur in only small sizes. They are found mostly in Russia, Finland, and California.

Grossular varies in color. It occurs chiefly in some shade of red, green, yellow, or brown, depending on the impurities present. When pure, grossular is colorless. A kind of grossular calledhessonitehas an attractive cinnamon color, and it is found mainly in Ceylon. Because of its color it can easily be confused with spessartine, which it closely resembles.

Andradite, a very common garnet, usually is found in shades of red, black, brown, yellow, or green. Some types of gem andradite have special names for different colors:topazolite, yellow;demantoid, green; andmelanite, sparkling black. The very valuable demantoid is found in Russia and Italy.

The name jade is applied to two unrelated minerals—nephriteandjadeite—that have somewhat similar characteristics.

Jadeite, the rarer of the two, is a sodium aluminum silicate that belongs to a group of rock-forming minerals known as pyroxenes. Its color varies from white to emerald green and many other colors. Jadeite is highly prized, and when it occurs as emerald green it is considered one of the most valuable gemstones. This kind of jade is found in many places, but the most important occurrence is in Upper Burma. Nephrite, a more common species, is a calcium magnesium iron silicate belonging to a group of rock-forming minerals known as amphiboles. The color varies from white to a dark spinach green and black. Among the places where nephrite occurs are New Zealand, Turkestan, Siberia, Alaska, China, Silesia, and certain parts of the western United States, notably in Wyoming and California.

This emerald green jadeite carving, dating from the Ch’ien-lung period (1736-1795), stands 6½ inches without the base. It was given to the Smithsonian as part of the Maude Monell Vetlesen collection.

Jade is not particularly hard (6½), but it is very tough, and this characteristic makes it an excellent material for carving. Even when subjected to punishing usage, jade resists chipping and wear. It was used for making tools and weapons by primitive peoples who lived in what is now Mexico, Switzerland, France, Greece, Egypt, Asia Minor, and in other places. The jade implements fashioned by these peoples have survived well the ravages of time.

The Chinese and Japanese prize jade highly. In their countries, tradition has assigned to jade medicinal and spiritual values, and has associated with it the cardinal virtues of charity, modesty, courage, justice, and wisdom. As a consequence, these peoples long ago developed the carving of jade as a high art. Among the magnificent Chinese jade carvings in the National Gem Collection are 130 pieces produced mostly during the Ching Dynasty (1644-1912), when the art of jade carving was at its peak. Many of these jades were carved in imitation of the revered bronze ceremonial vessels of ancient times. This collection was presented to the Smithsonian Institution in 1959 by Mr. Edmund C. Monell in behalf of the estate of his mother, Mrs. Maude Monell Vetlesen of New York.

This pale green jade vase of the Ch’ien-lung period is 14½ inches high without the base. It is one of a matched pair presented as part of the Maude Monell Vetlesen collection of carved jade.

A number of mineral species have produced cut gemstones that fulfill every necessary requirement of beauty, durability, and rarity, but their popularity and commercial success have been sharply limited because of insufficient supply. In some cases of even adequate supply such gemstones do not compete with other, more plentiful kinds that exhibit the same characteristics. The scarcity of these minerals does not diminish their standing as potential gem material—it merely points up the effect of accidental natural distribution of these species.

A magnificent set of 16 matched sphenes from Switzerland, gift of Nina Lea, almost encircles a 110-carat sinhalite (a rare magnesium borate) and a 22-carat kornerupine, both from Ceylon. The man’s gold ring indicates the sizes of these unusual stones.

Among the rarer minerals that produce good gemstones are cordierite, benitoite, euclase, phenakite, beryllonite, willemite, wernerite, danburite, datolite, axinite, brazilianite, andalusite, sillimanite, kyanite, kornerupine, enstatite, diopside, epidote, sphene, sinhalite, and orthoclase. Willemite, a rare zinc silicate found in only a few localities, is typical of these rarer minerals. The famous zinc mines at Franklin, N. J., produced a few large gemmy crystals of willemite, and some fine gemstones were cutfrom some of these. Willemite’s borderline hardness of 5 to 5½ and its extreme rarity effectively eliminate it from the gem market, but the collector who is able to obtain a good stone of this material is indeed fortunate.

Exotic gems that represent collectors’ items lie beside a 3¼-inch-long box of Russian lapis lazuli. The stones are (left row, from top) a 28-carat andalusite from Brazil, gift of Fred C. Kennedy, a 10-carat cordierite from Ceylon, a 29-carat apatite from Burma, and (right row) a 42-carat brazilianite from Brazil, a 13-carat euclase from Brazil, a 29-carat wernerite from Brazil, and a 61-carat orthoclase from Madagascar.

Some mineral species, although beautiful when cut, and prized by collectors, are entirely too soft, are too easily cleaved, or have some other physical weakness that renders them useless as commercial gemstones. Sphalerite, apatite, fluorite, calcite, cerussite, zincite, and hematite are included in this group. Sphalerite is typical; it produces brilliant and colorful gemstones that hold their own among other stones of great beauty. Unfortunately, this zinc sulfide, with a hardness of 3½ to 4, is so soft and cleaves so readily that it is very difficult to cut properly, and it cannot be used in jewelry.

The Smithsonian’s collection of gems continues to grow and improve rapidly, and it changes character constantly as important new gemstones are added and less important ones are retired. Approximately one-third of the gems in the collection in 1965 are itemized in the following list. Included are some of the largest gems of each kind, some of the more interesting stones, and some small gems notable for the places from which they came. Though listed by species and size, some of the larger stones are not included, and neither are most cabochons, rough opal, beads, carvings, and spheres. The descriptions listed include, in order, weight in carats; color; popular name or other description, if any; place of origin; and U. S. National Museum catalog number and name of donor. Gems in the Lea and Roebling collections usually are indicated by the letters “L” and “R.”

Seal of the Smithsonian Institution

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