Crystals

Crystals: Since the internal organization of mineral solids is so orderly, there should be, and frequently is, some external evidence of this order. If the solid crystal grows without external interference it will end up with flat, shiny surfaces, or crystal faces, that are parallel to layers of atoms within. It is even possible, by measurement of the angles which these external faces make with each other, to learn something of the atomic arrangement within. This is the business of the crystallographer. Since gem material is usually of high purity and has normally formed under ideal conditions in the earth, it is often found in transparent, well-formed crystals with good external faces. Often they are so well formed with regular, shiny faces that they give the impression of having already been cut and polished as gems. In size they may vary from microscopic individuals up to single crystal monsters weighing several tons each. Good, clear, clean, gem-stone crystals, except for quartz, seldom are found in large sizes.

All solids, with minor exceptions, have orderly internal atomic arrangements and so are classed as crystals. The modern crystallographer studies these arrangements by using specialized X-ray techniques. Also, less frequently, he will study the morphology or external shape and symmetry of these crystals. The science has advanced to the point where it is possible to determine just which kinds of patterns and symmetries may occur in natural and man-made crystals. All crystals, it has been discovered, can conveniently and logically be divided into thirty-two different kinds of symmetry groups or crystal classes.

For the sake of further convenience and simplification, it is possible to group these thirty-two classes into six crystal systems, all classes in a given system having some important symmetry in common. The systems are: isometric, tetragonal, ortho-rhombic, monoclinic, triclinic, and hexagonal. The gem minerals can often be identified and distinguished from each other by the crystal systems into which they fall as they grow according to the dictates of their atomic structures. Beryl, in all its varieties such as emerald and aquamarine, is hexagonal, as is corundum with its varieties ruby and sapphire. Spinel is isometric, like diamond rings and garnet, while topaz is orthorhombic and zircon is tetragonal. Everything that a gemstone rings is, how it looks, how it wears, and how it takes cutting and polishing, depends directly on its chemical composition and its internal structure. What a gemstone's characteristics are and how they arise makes an interesting study.

Silicates

Aquamarine, emerald, tourmaline, topaz, zircon, peridot, spodumene, and garnet are gem minerals known by the general name "silicates" and contain both silicon and oxygen as their major constituents. Ruby, sapphire, chryso-beryl, and spinel are "oxides," containing oxygen as a major constituent. As already mentioned, each kind of atom is limited in the kind and number of other atoms it can join. The chemist that are also making diamond engagement rings, through the years, has learned to predict the possible combinations and has developed very accurate methods of checking them in the laboratory. He can make almost innumerable combinations of elements in the laboratory, predicting in each case how they will combine with each other. He can also determine the kinds and relative quantities of atoms present in a mineral sample and use a standard method of noting them. His typical analysis of a mineral might show that there are equal numbers of zirconium (Zr) and silicon (Si) atoms present and four times as many oxygen (O) atoms. His notation, then, would read ZrSi04. This is the chemical notation or formula for the gem mineral zircon. Thus, the formula for aquamarine is Be3Al2Si6Oi8—a beryllium aluminum silicate; for chrysoberyl it is BeAl204—beryllium aluminum oxide.

All this seems simple enough until it develops that the chemical formulas for ruby and sapphire are identical—A1203. If absolutely pure, this aluminum oxide, A1203, is colorless. Ruby, however, is red, and sapphire by definition is any color except red. As the formula indicates, they are actually the same mineral, but ruby is aluminum oxide containing very small traces of the element chromium which cause it to have the red color. Sapphire seems to get its colors from tiny traces of iron or titanium, or both together. Certainly, this is a case where chemical impurities gathered by a mineral during its formation produce highly desirable results.

Gemology science

The science of gemology is i concerned with investigating and establishing facts about gems and gemstones. Somehow, because gems usually are objects of monetary value, it is often difficult to think of them in scientific terms. Questions about where they come from, what they are made of, and how they can be distinguished from one another usually take second place to questions about their value. However, these other questions must be answered first, before decisions can be made about value. For example, the market values of look-alike quartz and topaz differ greatly. Proper identification of a suspected topaz is crucial before a relative price can be assigned to it. Aside from pricing problems, other kinds of serious mistakes can be made because of faulty identification. Two of the more famous rubies in the world, the Black Prince's Ruby and the Timur Ruby, are not rubies at all, but spinel. Even so, they are extremely important stones because of their historic past and their prominence, among the British crown jewels. The science of gemology is quite different from the lapidary art, which deals with techniques for cutting, polishing, and generally shaping gemstones for ornamental use by themselves or in jewelry. Cutters and carvers and craftsmen through the centuries have refined the techniques and equipment for gem cutting. Lapidary work has become a joint venture for artist and craftsman, and it leans heavily on the science of gemology. Certainly, a lapidary must know how his gemstone is going to behave and how to turn its characteristics to advantage before he begins to work on it.

To most people who talk about gemology and about gems in general it becomes obvious that, through careless usage, some of the basic vocabulary has become confused. To set the record straight, "gemstones" are the specially treasured minerals found in the earth and "gems" are the objects fashioned from them. "Jewels" are gems that have been prepared for mounting in jewelry or other objects of art. Remember gems are used also for Wedding Bands, Wedding Jewelry

Why are only certain natural mineral samples specially treasured as gemstones? Because gems can be cut from them that have at least some of the qualifying characteristics: brilliance, beauty, durability, rarity, and portability. If the gem also happens to be "fashionable" it acquires status. Partial qualification is more often the rule, because seldom does a gem have a large measure of all these attributes.