Gem Collectibles

Amblygonite: This is a lithium alumi­num fluophosphate sometimes found in trans­parent, gem-quality crystals. It varies from colorless to yellow, has a hardness of 6, and tends unfortunately to develop its perfect cleavage if stressed too much. Gem-quality amblygonite is found mostly in Sao Paulo and Minas Gerais, Brazil.

Andalusite: Named for Andalusia, Spain, where it was first found, this species is an aluminum silicate with a hardness of 1y%. Its color varies from green to greenish-brown. Most of the gem material comes from the states of Espirito Santo and Minas Gerais in Brazil, where it is found in rounded pebbles.

Apatite: Although it is a very common mineral occurring in enormous crystals and at innumerable places around the earth, apatite is seldom found in transparent, gemmy crystals or fragments. The mineral is a calcium phos­phate containing fluorine or chlorine and frequently other elements. A hardness of only 5 and its brittleness make it useless for ordi­nary gem uses, even though it occurs in a wide variety of good colors.

Cerro de Mercado in Mexico produces finger-size, golden-yellow, transparent crystals. Mogok in Upper Burma has yielded good blue stones. Yellowish-green, violet, and deep-blue stones have appeared elsewhere and even apatite cat's-eyes are found in Ceylon.

Augelite: A colorless, hydrated alumi­num phosphate with a hardness of only 5, augelite is a collector's item only because of its rarity; it has no particularly attractive or unusual features. Cuttable crystals have been found in the United States and in Bolivia.

Axinite: This is usually found in dark cinnamon to greenish-brown crystals. Their shapes are reminiscent of an axe head, which accounts for its name. It is a chemically com­plex calcium aluminum borosilicate and is usually too dark in color to cut into attractive gems. When suitable light-colored material is found for cutting, the hardness of 7 gives it sufficient durability to make it worthwhile. Cutting-quality crystals have been found in Switzerland, France, and Baja California.

Benitoite: In the gem collection of the Smithsonian Institution is a 7.5-carat, beauti­ful blue, cut stone that resembles a sapphire, but with exceptionally good fire. The fire is actually better than that of diamond, but is subdued by the blue color. The stone is beni­toite, a very rare barium titanium silicate named to honor San Benito County, Califor­nia, the only place it has ever been found. The 7.5-carat gem is the largest cut stone in exist­ence for this species. A hardness of 6]/2 gives it satisfactory durability. With all its excellent qualities, it cannot be a commercial gem be­cause it is so rare.

Beryllonite: The best beryllonite of gem-cutting quality, a very rare beryllium sodium phosphate, has been found at Stoneham, Maine, with other pegmatite minerals. Like augelite, it is colorless, looks glassy, has a hard­ness of only 5, and offers little except its great rarity.

Brazilianite: A pegmatite in Minas Gerais yielded in 1944 some superb, large gem crystals of a hydrous aluminum sodium phosphate previously unknown to science. It is a brittle substance with a hardness of only 514 and is otherwise almost undistinguished as a gem material. Its good yellow to yellow-green color makes it a suitable addition to the connoisseur's collection.

Cordierite: When cordierite, a magne­sium aluminum silicate, occurs in gemstone quality, as it rarely does, it is known by one of several gem names. The most familiar of these to the jeweler and gemologist is "iolite," a word derived from the Greek, which alludes to its violet color. Perhaps the most outstand­ing characteristic of the gem is its very strong pleochroism. When viewed in the three dif­ferent crystallographic directions, it is dark purplish-blue, yellow, and light blue. A strong bluish color is preferred for cut stones, but there is always a tendency for the color to be too intense. Well-colored iolite gems are rather rare. The hardness is somewhat above 7. Best known of its rare occurrences as a gem-stone are the gravels of Ceylon and Burma, and scattered finds in Madagascar and India.

Danburite: As often happens, the locality at Danbury, Connecticut, which first yielded this species never produced any of gem quality. Colorless, cutting-quality danburite has come from Mogok in Burma, Bungo in Japan, and San Luis Potosi in Mexico. A pale pink variety also occurs in Mexico. Good yellow stones have come from Burma and Madagas­car. Danburite is a calcium borosilicate with a hardness of 7, and its gems are brilliant.

Diopside: This is a calcium magnesium silicate. Most of the gemstones it yields are green to brownish-green because of the pres­ence of iron, which always replaces some of the magnesium. However, gems have also been cut from material that is colorless, blu­ish, or brown. Even good cat's-eye diopside is plentiful. Diopside has a hardness of only 5y2 and a strong tendency to cleave, which limits its usefulness as a gem. Good green gem-stones have been found in Piedmont, Italy; Zillertal, Tyrol; St. Lawrence County, New York; Ceylon, Madagascar, and Brazil. There is a chromium-bearing variety with a livelier green color which occurs at Kimberley, South Africa, and also at Outokumpu, Finland, and as cat's-eyes at Mogok, Burma.

Ekanite: Few living men have had the pleasure of finding new gemstones to bear their names. Mr. Ekanayake of Ceylon found the first sample of a new greenish gemstone in the Ceylon gravels in 1953. By 1961 the ma­terial was properly described and named in his honor and several new samples were found. This rare calcium thorium silicate has a hardness of almost 61/2 but, unfortunately, is strongly radioactive. Asterism is common in the material with some gems showing good four-rayed stars.

Euclase: Well-formed natural crystals of euclase are rare enough to be worthy of a col­lector's attention. The mineral is a beryllium silicate with a hardness of 7l/z- Often colorless, crystals may also be completely transparent with strong enough shades of greenish-blue to be attractive gem material. The name alludes to its characteristic of cleaving rather easily, which reduces its value as a durable gem and turns the cutting operation into a gamble. Most cutting-quality euclase is found near Ouro Preto, Brazil, but it is known elsewhere.

Fluorite: Perhaps a discussion of fluorite —calcium fluoride—would be better placed in a text about industrial minerals. It is used in vast tonnages for smelting iron, manufactur­ing insecticides, and in the chemical industry generally. It is too soft (4), cleaves too easily, and has little to offer as gem material except its wide range of attractive colors. It may oc­cur in several shades of pink, yellow, yellow­ish-brown, lavender, violet, blue, or green. Faceted cut gems are inexpensive and are made only for collectors. However, larger masses are sometimes carved. The carvings, though easily executed because of the softness of fluorite, tend to be very fragile because of the easy cleavage. Rather compact crystal­line masses of a violet, purple and blackish fluorite, found at Derbyshire, England, are known as "Blue John." This material is a bit more durable and has been carved for cen­turies because of the attractiveness of the colors and patterns of polished masses.

Hambergite: It is questionable whether the natural specimens of this rare beryllium borate should ever have been cut into gems; \ But because collectors are always looking for something unique, some gems have been cut from transparent crystals that are free of dis­tracting inclusions. The mineral is colorless, has a glassy luster and very little color disper­sion. Cut glass would be just as attractive. However, a hardness of lVz gives it some dur­ability. The best cutting-quality crystals have been found in Madagascar.

Hematite: Like fluorite, this iron oxide is more at home among industrial minerals since it is the most important ore of iron. Now and then the mineral is found in pure, brilliant but opaque, black-looking crystals which lend themselves to certain gem purposes. These crystals have a hardness of 61/2 and no tendency to cleave or fracture easily, so that they can be cut without too much trouble and will take a brilliant polish. Hematite has been used to make black beads which look like jet black pearl. Because it is so easily carved it has been commonly used to make cameos, intaglios, seal stones, and various kinds of ornaments. "Alaska diamonds" are really hematite.

Kornerupine: There is little chance that kornerupine, a rare magnesium aluminum iron borosilicate, will ever be a popular gem-stone. All the material found so far in Green­land, Madagascar, Ceylon, and elsewhere is an odd shade of green or a greenish-brown. The typical gravel pebbles of the gemstone have a hardness of 61/2 and show a strong di-chroism. In one direction they are greenish to yellowish and in another they are brownish to reddish-brown.

Kyanite: Like andalusite and sillimanite, kyanite is an aluminum silicate. Its name re­fers to the normal blue color of this common species. Color in the very rare pieces of gem-cutting quality varies from blue to green. Kyanite is very difficult to cut. One problem is a marked variation in hardness—from 7 when measured in a direction across the crystal, to 5 when measured down its length. It has a strong tendency to cleave into flat blades. Beautiful sapphire-blue gems have been cut with dif­ficulty from North Carolina kyanite.

Orthoclase: Earlier, this member of the feldspar family of minerals was described under moonstone, its most renowned variety. However, there is a beautiful, iron-bearing, transparent, golden yellow variety found at Itrongay, Madagascar. It's hardness of 6, rich color, and rarity make it popular with col­lectors, but it has little acceptance among commerical gems.

Painite: An extraordinary, mysterious gemstone, painite is a calcium borosilico-alu-minate. The mystery arises from the fact that only a single crystal has ever been found in nature. It was recovered from gem gravels near the village of Ohngaing in Upper Burma by Mr. A. C. D. Pain in 1951. The deep-red min­eral was determined to be a new species. How­ever, its hardness (lVz), color (red), density (4.01), and other characteristics make it diffi­cult to distinguish from garnet, and it is quite possible that cut stones of painite already exist in gem collections masquerading as garnet. Eventually, the very lucky collector who is able to discover one will probably do so by examining its crystallography; painite is hex­agonal and garnet is isometric.

Petalite: Again, this mineral—a lithium aluminum silicate—has been cut only to satisfy the collector's whim. It has a hardness of no more than 6, cleaves under stress, and tends to be brittle. What is perhaps the largest cut gem for the species is in the collection of the Smith­sonian Institution; it weighs 55 carats and looks like a well-cut piece of glass.

Phenacite: Because well-cut gems of phen-acite look very much like the common rock crystal variety of quartz, they have never had much commercial value. The mineral is some­what harder than quartz—almost 8 on Mohs' scale— but it is colorless, so that it has no other advantage except rarity, which counts heavily among gem collectors. Good cutting material has been found in some quantity in the Ural and Ilmen Mountains in Russia, and near San Miguel di Piracicaba, Minas Gerais, Brazil.

Pollucite: Rarity is almost the only claim that pollucite has to a position among gems. Only 6i/2 in hardness, it is colorless and glassy, and its refractive index and dispersion are too low to make the material attractive. It is a cesium aluminum silicate originally found at Elba, though the best-known gem-quality spec­imens are from Newry, Maine.

Proustite: It is difficult to imagine a gem with a hardness of only Zyk—so soft it can be scratched with a fingernail. At the same time, this silver arsenic sulfide also has a disagreeable tendency to turn black over a period of time when exposed to light. Normally, as mined, it is a bright, rich red—a reason of sorts for the material being cut for gem collectors.

Rhodizile: Found near Russia's Ural Mountains and in Madagascar, this rare borate (sodium potassium lithium aluminum berylli­um borate) is one of the few borate minerals ever cut into gems. It lacks any distinctive color or fire. However, it cuts well, has a de­sirable hardness of 8, and has been cut into small but flawless gems for the collector.

Scapolite: Several mineralogical names have been applied to the scapolite group of mineral species: dipyre, wernerite, marialite, meionite, and mizzonite among them. The plethora of names arises because the composi­tion of scapolite varies all the way from a sodium aluminum silicate (marialite) to a cal­cium aluminum silicate (meionite). Various other names are used for intermediate mem­bers of this series. Generally the hardness is 6 for all scapolites, of whatever composition. Luster is glassy and dispersion is low, but stones may be attractively colored in yellow, pink, or violet, as well as the usual white and colorless. Some stones have excellent chatoy-ancy, so that good scapolite cat's-eyes have been cut. When the chatoyancy is diffused and does not produce a sharp eye, cabochon-cut stones may strongly resemble moonstone. Burma, Madagascar, and Brazil have produced the best scapolite for faceted and cat's-eye gems, but the mineral is found in opaque, nongem masses in Canada, Mexico, and elsewhere.

Sillimanite: The mineral species silliman-ite, an aluminum silicate, is chemically identi­cal with andalusite and kyanite. Among gemol-ogists it is better known by the name fibrolite, a name referring to the fibrous nature of most of the material. The gem-rich gravels of Mogok in Burma have produced some fine, transparent bluish stones suitable for faceting. Probably the finest of these cut gems is a 19.84-carat gem in the collection of the Geological Survey Museum in London. Gray-green cha­toyant fibrolite has been found in Ceylon and fine, dark, almost black cat's-eyes have been recovered in South Carolina. Because of its fibrous structure, sillimanite varies from 6 to 71/2 in hardness.

Sinhalite: The discovery of sinhalite in 1952 arose from an examination of an unusual sample of the gemstone peridot of a brown color rather than the usual strong green. It proved to be a new mineral species—a magne­sium aluminum iron borate—and not peridot at all. It was named after Sinhala (Ceylon in Sanskrit), where it is found in the gem gravels. This brown or greenish-brown gemstone has few distinguishing features, and being rather rare, is little valued except among collectors.

Sphalerite: Seldom do we encounter gem-stones that are more important as ores than they are as gems. This—like fluorite and hema­tite—is one of them. Sphalerite—zinc sulfide— is a major ore of zinc-which is mined in tremendous tonnages in this country and elsewhere. Infrequently, a few transparent, gem-quality pieces are found showing fine yel­lowish-brown to orange-brown color instead of the usual dark brown to black shades. These are sometimes cut for the collector because, in addition to the attractive color, sphalerite has a very large color dispersion which gives it a fire more than three times that of diamond. The misfortune of this beautiful gem species is that, with a hardness between 3 and 4, it is too soft for almost any practical use.

Sphene: This is another gemstone with a strong fire—greater than that of diamond. At 014 on the Mohs scale, its hardness is more than that of sphalerite, but not quite high enough to qualify it for general jewelry purposes. The golden-yellow cut gems of sphene, with their strong fire, are particularly attractive, but yellowish-brown, orange-brown, and green stones are also very fine as long as the color is not so intense that they become almost opaque. Switzerland, Burma, and Baja California are the best-known sources.

Taaffeite: No more than a half dozen gems of taaffeite, a rare beryllium magnesium aluminate, are known. All have been found by optical examination of cut gems thought to be spinel. Unlike spinel, some few of these stones were found to exhibit double refraction. Curiously, gem-quality taafeite has never been found in place in nature. Identification is difficult except by observing the double refrac­tion, because taaffeite has a hardness, density, and refractive index very much like those of spinel. Most of the gems, probably originating in Ceylon, are pale lavender pink, but at least one is a deeper, amethystine color. The gem is named after its discoverer, Count Taaffe, who found the first gem in 1945.

Tektite: There is considerable scientific controversy about the origin of tektites. These glass-like blobs, of varying dimensions up to perhaps three inches in diameter, often have strangely pitted, fissured, rounded, or other­wise oddly marked surfaces. The most exciting theory holds that they are extraterrestrial, hav­ing traveled through space until caught by the earth's gravity to come raining down on the surface. It is true that they are found only in selected spots on the globe, such as in Western Moravia and Bohemia near the Moldau River (Moldavites), and in parts of Australia (Aus-tralites). It is true, also, that although they resemble blobs of obsidian—a volcanic glass— their chemical compositions are unlike any known obsidian. Tektites provide transparent cut gems of a brown, brownish-green, or green color which are no more attractive or interest­ing than colored glass, except for the possibil­ity of their celestial origin.

Willemite: Even for gem collectors it is sometimes difficult to acquire a cut gem of willemite. This zinc silicate is not rare at all, since it is mined by thousands of tons in the area of Franklin, New Jersey, and smaller quantities are found at occurrences around the world. However, crystals of gem-cutting qual­ity are extremely rare and only a few have been discovered at the Franklin mines. The green­ish-yellow gems are too soft (5*4) and have a rather resinous luster; their interest is almost entirely for their rarity.

Zoisite: Any text or compendium on gems published more than two years ago will have little to say about the gem occurrences of zoisite, a hydrous calcium aluminum silicate. It was known then only as an attractive, pink, opaque, ornamental stone called thulite, or asa brilliant green, granular material from Tanzania containing bright red, but opaque, ruby crystals. Suddenly in 1968 and 1969, quantities of extremely attractive gem zoisite began to flow into the markets from prospects near Arusha, in Tanzania. This material is in flawless crystal fragments exhibiting excellent pleochroism. The predominant colors are bright sapphire blue and rich purple. When cut in the appropriate crystal direction, or when heat-treated, the rich color rivals that of fine blue sapphires. A hardness of only 6 and a slight tendency to fracture have not aroused any popular resistance to the introduction of this new gem because it is so very beautiful. Its origin in Tanzania quickly inspired the vari­ety name of Tanzanite for the gem.