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The organic products used in jewelry are quickly affected by heat.’Pearls are completely spoiled; they turn brown and split. Amber burns with a camphor-like smell, giving off black fumes. Coral loses its color and decrepitates.
One other result of heating may be mentioned here, and that is the property which a few gem stones possess of emitting light, known as phosphorescence. This must not be confused with fluorescence. Pieces of quartz, when rubbed together in a dark room, give off a phosphorescent light, while heated fluorspar displays a very bright effect. Exposure to strong sunlight is sufficient to produce this effect in some minerals. Diamonds, especially yellow tinted specimens, are highly phosphorescent; apatite, a mineral occasionally cut as a gem stone, is slightly phosphorescent. Such effects may be more easily observed if the specimens are transferred quickly from the sunlight to a dark room.

The application of heat to improve or alter the color of stones needs considerable care, patience, and experience. Many stones are spoiled in such attempts to improve on nature and increase their commercial value. Zircon and the different varieties of quartz are perhaps the chief victims of man’s enterprise in this direction, and it is only the cost and the rarity of raw material thai limits greater experiment. But the artificial perfecting of precious stones may yet be one of the achievements of the future chemist or physicist.

Some brown zircons lose their color when heated, and become a brilliant white on cooling, at the same time increasing greatly in luster and brilliance. Other pale blue zircons may have their color intensified, which may or may not remain. Rubies and some other stones will change their color, which returns on cooling. Minute faults in some rubies and emeralds have been eliminated by very careful heating, but this is a risky procedure as the stones may crack. Some green tourmalines are rendered more brilliant by heating, while some aquamarines change to a darker blue shade. The same may be said of some golden beryls, which may be changed to a pale blue.

The majority of the carnelians we see on the market have been the subject of applied heat. Most were originally sards, the dark brown having been driven off, giving place to the attractive flesh color. Again, many of the brown and yellow transparent <|iiartz, the consistently misnamed “topaz,” are the product of 11 eating smoky quartz, while the yellow citrine and treacle brown “topaz quartz” are, in many instances, derived by heating ame-lliysts. At about 500° C, many, but not all, South American amethysts will change to a deep, brownish-red or orange color, sometimes approximating to a rich garnet shade. These stones are sold as Madeira Topaz, Spanish Topaz, or just “Topaz.”

A moderate heat is sufficient to make many amethysts and all (Urquoises fade in color. Further, if a stone contains water in its composition, it will be quickly affected. Opal is an example. This stone quickly cracks, loses its opalescence, and is entirely spoiled. Diamond will stand great heat, losing nothing but its superficial brilliancy, which can be regained by polishing. But at a very high temperature, it burns in air and oxygen, producing carbonic anhydride.

Some stones become clouded on heating, some fuse, while others are infusible. The degree of fusibility is important when making a qualitative analysis, and the results of submitting stones to the so-called “dry test,” which involves the use of a blow-pipe, are most necessary to the chemist who is seeking to ascertain the constituents of a given mineral. Some notes on the fusibility of gem stones under these conditions are given in a later chapter.

Numbers 1 and 2 are the most convenient to use, but any or all can be made up and kept in glass test tubes ready for use. It will be realized that all varieties of quartz, whose specific gravity is about 2.66, will float on bromoform; many similarly colored stones will sink. Some of the liquids are poisonous to handle, others are unstable, so certain precautions must be taken in their use.

Another method which involves the use of an ordinary jeweler’s balance and very little other apparatus will determine the specific gravity of a stone fairly accurately. This method is based on the well known principle that, when a solid is totally immersed in water, the apparent loss in weight is equal to the weight of water displaced. The stone must first be weighed, and then weighed again while totally submerged in water. The difference between these two weights, the apparent loss, is the weight of water displaced. This figure, divided into the weight in air, gives the specific gravity of the stone.

Any delicate balance can be easily adapted. For weighing in water, a piece of thin wire coiled to act as a holder or cage for the stone may be used. This can be suspended from one arm of the balance so that the cage reaches into a small beaker of water. The beaker must stand free of the balance, and the weight of the wire must also be ascertained.
For instance, the following figures will be given as an example, carat weights being used.

Weight of wire.    .80 carats.
Weight of wire and stone.    13.65 carats.
Weight of stone.    13.65 - .80 =    = 12.85 carats.
Weight of wire partly immersed.    .72 carats.
Weight of wire and stone partly immersed.    10.38 carats.
Weight of stone in water.    10.38 — .72 =    = 9.66 carats.
Loss of weight of stone in water.    12.85-9.66    = 3.19 carats.
Specific gravity of stone.    12.85
= 4.02.
3-i9

If desired, a counterpoise of the same weight as the wire may be used, and if another of the same weight as the scale pan on the side from which the cage is suspended is used, this scale pan may be dispensed with altogether. Weighing in water will thus be facilitated.
In order to obtain more accurate results, certain additional measures should be taken. Distilled water at a temperature of 60 ° F should be used, and the weight of the atmosphere might be taken into account. Surface tension also produces small errors; the high surface tension of water, which makes it cling to the wire cage and also causes bubbles, makes results inaccurate. In order to avoid this, other liquids are sometimes used. Alcohol, toluol (sp.g. .87), carbon tetra-chloride (sp.g. 1.59), and ethylene dibro-mide (sp.g. 2.18) are among these, and at the laboratory of the Precious Stone Section of the London Chamber of Commerce, Anderson and Payne have recommended the use of the last. When using any of these liquids, it is necessary to allow for the density of the liquid at the temperature when the experiment is being carried out. Tables showing details of such necessary corrections may be obtained. But for ordinary practical purposes, the method first described should give sufficiently accurate results.

Specific gravity may be ascertained without damaging most stones since very few are affected by water. Turquoise, opal, and porous stones should not be tested in liquids other than water. There are balances which have been specially devised for taking specific gravities, and among these are the aerometer, Walker’s balance, and Jolly’s spring balance. For small fragments or powdered minerals, a specific gravity bottle may be used. Reference to these is made in a later chapter.

In general, crystalline solids expand on being heated, and the amount of expansion is different in different directions. The expansion in volume is equal to the sum of the linear expansion along the principal axes, thus showing that the crystal form of a stone will have some bearing on the heat effects. But this is a matter for those who can experiment in laboratories. Here wc will note the effect of heat on gem stones in general, for in recent years, attempts to alter the color of certain varieties by heating have been on the increase. Some success has been obtained, mostly at the expense of experiment. The theoretical causes of many of such changes are not yet fully understood.

In some instances, it may be the result of a re-arrangement of molecular structure; in others, some chemical change may take place. For instance, if the color is due to a minute portion of included organic matter, heat would permanently destroy the original color. If the color is due to inorganic matter, such as a metallic oxide, the original color may return on cooling, or it may be changed altogether. But the general effect of heat is to discolor stones.

If a very high temperature is reached, most gem stones are completely spoiled. Those which develop pyro-electricity have already been noted. Others, which change color when certain temperatures are reached, are discussed under their individual headings. For instance, sherry colored topaz loses its color completely on being heated, yet on cooling it changes to an attractive pink. Many of the pink topaz on the market have been artificially “pinked” by packing in magnesia, charcoal, or Plaster of Paris, and then being slowly heated. Incidentally, this is a practice seldom carried out now with topaz, and most of the heat treated stones are found in old mounted jewelry. The stones are often foiled to give extra depth of color.

A good method of distinguishing stones is by ascertaining their specific gravities since each variety of gem stone possesses a gravity which is very nearly constant. Reference to tables, such as the one given in the Appendix, will either immediately show what the
stone is or limit its identification very considerably. If it were possible to take gem stones all of the same size and weigh them, it would be found that the weights would be different. In other words, their weights will vary according to their denseness, and if these weights can be compared, each stone of the same volume being used, a useful constant can be obtained by which a stone may be distinguished.

By specific gravity we mean the weight of any solid compared with the weight of an equal volume of water at 40 C. At this temperature, the weight of one cubic centimeter of water is one gram, and this is the standard with which all solids are compared. For instance, one cubic centimeter (1 c.c) of carnelian would weigh 2.66 grams, and the specific gravity (sp.g.) of carnelian is therefore designated as 2.66.

There are several methods of obtaining the specific gravity of a stone, some being only suitable where laboratory apparatus is at hand. A quick method, which is only comparative but still very useful, depends on the fact that a solid will sink in a liquid having a lighter density than itself, and will float if its specific gravity is lighter than the liquid. If the density of the liquid is first known, a good idea as to the specific gravity of the stone will be obtained. Since stones are relatively heavy, solutions having a high density must be used. Those most frequently chosen are:
1.    Bromoform. Sp.g. 2.90. This is a yellowish liquid, which will mix with benzine, toluene, and alcohol, and it can thus be diluted with any of these lighter liquids to alter its specific gravity. It is fairly cheap to use.
2.    Methylene iodide. Sp.g. 3.32 A liquid which will also mix with the above named lighter liquids. It is much more expensive (ban bromoform.
3.    Klein’s solution. This is a saturated solution of cadmium-boro-tungstate with water, with a sp.g. of 3.28 at 150 C.
4.    Sonstadt’s solution. A saturated solution of potassium mercuric iodide in water, sp.g. at 150 C being 3.18.
5.    Clerici’s solution. This is colorless, having a sp.g. of 4.15, I)iit its density may be lowered by adding water. It contains thallium salts and is poisonous.
6. Retger’s solution. A double nitrate of thallium and silver, sp.g. at 150 C being 4.6.

Dust in the air contains certain small amounts of quartz and other impurities whose hardness is about 7. For this reason, stones of about 7 and under are scratched in wear fairly quickly if worn constantly, and it should be noted that emerald, quartz, and opal are amongst these.

In many minerals, there are certain directions in which a blow with a sharp instrument will cleave a specimen, the parting portions showing smooth surfaces. This tendency to split easily in certain directions with smooth surfaces is known as cleavage, and the cleavage planes are directly connected with crystallographic form,’ the direction being parallel to, or following, a possible face of the crystal. Octahedral cleavage gives four planes of cleavage, cubical gives three planes, prismatic gives two, and pinacoidal or basal cleavage gives one plane of cleavage only.

A stone may be hard, however, and yet be easily cleaved. The most important example of this is the diamond, which possesses cleavage directions carefully followed by the lapidary when fashioning the rough stone in its initial stages. Cleavage is an important property to be considered in the working of many gem stones, but some do not possess this quality at all.

Cleavage should be distinguished from hardness and fracture. Some stones, although comparatively soft (jadeite is an example) are very difficult to work on account of their peculiar internal structure. Fracture, characterized by an irregular surface in distinction to the smooth, flat surfaces of cleavage, may be of help in distinguishing a stone. If it breaks with a concave or convex fracture, showing concentric undulations somewhat resembling the lines of growth on a shell, it is said to be conchoidal. This type of fracture is shown in quartz, obsidian, and glass. Other types of fracture are even, uneven, hackly (when the surface is studded with jagged elevations), and earthy. Most gem stones are, of course, brittle, and they do not possess the flexibility and similar properties which characterize many metals.

Here we are referring to electrical properties in a general sense, ;md although these are of great interest, they are not important as distinguishing features of any particular stone. Of course, not all gems display this property, but a few develop electricity if friction, pressure, or heat is applied. When electrified, such stones will repel similarly and attract dissimilarly electrified bodies, while they will transfer their property to neutral bodies. Others exhibit polarity, that is, one end or side is charged with positive, mid the other with negative, electricity.

Friction will develop electricity in many minerals, the most prominent being topaz and amber among gem materials. The rubbing of amber, which results in negative electricity being produced, is well known to many who try to use this as a test for this material, although it is no proof of its identity. Incidentally, electricity is so named from the Greek word for amber, elektron, for this property was first observed by rubbing pieces of amber with silk by Thales in the Sixth Century B.C.

As a general rule, stones exhibit positive electricity only when polished, and negative electricity when unpolished, with the exception of diamond. Some crystals, when heated to a certain temperature, exhibit electrical properties which cause them to display polarity resembling that of a magnetic needle, and this property is termed pyro-electricity. It was first observed in tourmaline, but topaz, diamond, and many types of quartz also possess this quality.

If a crystal of tourmaline is heated to a temperature ranging between 10° C and 1500 C and then suspended by a fine silken thread, it will behave like a magnet having positive and negative poles. ‘As the crystal cools, its polarity becomes reversed. Tourmaline crystals, when perfect, are often terminated by different crystalline faces at the two ends, and other minerals which possess this peculiarity (known as hemimorphism) often display pyroelectricity. Topaz, prehnite, smithsonite, and axinite are examples.
Pyro-electricity in a stone may be detected by an apparatus in which a mixture of red lead and sulphur powders are blown through a fine sieve on to the stone. The resulting friction causes the particles to become electrified, red lead positive and sulphur negative, and these are attracted by charges of opposing signs. The color, red or yellow, of the powder will show the charge to be either positive or negative respectively.

Jewelers often use a small file for hardness testing. If the file cuts into the stone, a fine powder is produced, thus showing that the stone is softer than the file. The hardness of a jeweler’s file, which is finely cut and of hard steel, is about 6 1/2. It will mark feldspar but will not scratch quartz. Glass and pastes are marked by a file, their hardness varying from 4 1/2 to 5 1/2. For use in jewelry, stones should withstand this file test, but many well known varieties are softer, their other outstanding qualities overcoming this deficiency.
Tests on transparent and cut stones should be applied with discretion since a specimen may be easily disfigured by a deep file mark. It should therefore be carefully tested on an edge, preferably the setting edge. The sound made by filing and the color of the powder produced are also guides to hardness. But in general, this test is more useful with rough stones than with cut gems; there are other tests for distinguishing the latter without risking injury to the beauty and value of the specimen.

It must be added that some stones vary slightly in their degree of hardness. This will depend in a few instances on their place of occurrence, in others, on the direction in which they are tested, for instance, the hardness of diamonds varies slightly, the Borneo stones being harder than the South African stones. Different faces of the same stone may also vary in hardness, this feature being due to the internal molecular structure. An outstanding example is kyanite, a mineral whose hardness is 5 in one direction and 7 in another. But generally speaking, the limits of variation are very close to each other in most stones.

These are the most important of all, since on them largely depends the beauty of the various gem stones. In addition, the gemologist makes use of these characteristics to determine the nature of a given specimen, and with some practice and the use of certain instruments, a stone may be quickly and accurately defined The determination of the optical properties has the advantage of freedom from any risk of damage, and in most instances the specimen need not be removed from its setting if it is in a piece of mounted jewelry. The lapidary also, who cuts the rough stone, must be conversant with its optical properties, otherwise he will not get the best effect from the rough material.

For the purposes of discrimination, the two most useful instruments are the refractometer and the dichroscope. In most instances, the former gives the practised hand a definite reading, and from this reading, known as the refractive index (R.I.), the specimen may be distinguished. The dichroscope shows certain light effects in some instances, and their presence or absence will limit the nature of the stone under examination to a few species. This latter instrument costs very little; the refractometer, no matter which type is used, will cost more. When the necessary knowledge to use these two instruments has been acquired, they are the best (wo investments for those who have to decide quickly what a given specimen might be. To the jeweler, they are invaluable. But the use of these instruments involves some knowledge of light and particularly how rays of light are affected when they fall On such bodies as gem stones. It will be seen that crystal forma-I ion has a direct bearing on this large subject, of which we will touch only the fringe.
Here, we will assume that light consists of rays and travels in a straight line in order to explain various optical phenomena. These assumptions are not strictly correct. In describing the ac-(ion of light, we generally speak of rays, which may be regarded as portions of light enclosed by a hollow cone of very small angle, diverging from or converging to a point called the focus. The space or material through which light passes is termed a medium, and light travels in a straight line through the same homogeneous medium.
When rays of light, traveling in one medium, e.g. air, come in contact with the surface of another medium, e.g. a gem stone, they air, in general, broken up in three different ways. Some are reflected from the surface of the stone, others enter the stone and are refracted within the stone before emerging again, and the remainder is scattered or diffused. Reflected and refracted rays

follow definite paths, and their behavior has resulted in the establishment of certain “laws” which are of the utmost importance to the gemologist.

With the development of analytical chemistry, the blowpipe method has given way to the “wet” method once more, but this is not very suitable or useful to the gemologist as it is often restricted to minerals which are soluble in some liquid. A recent method is the noting of calorimetric reactions in the presence of a variety of reagents. By these means, a drop of the reagent selected is allowed to come into contact with a drop of the solution ‘being tested, and the resulting color is sufficient to indicate which elements are present. The method in use and the reagents required are described in a paper read by J. H. Watson on November 1st 1934, before the Mineralogical Society of London. The details do not come within the scope of this work, nor would the results be of much practical use to the gem dealer or collector.

Actually, an analysis of the earth’s crust, based on a series of averages taken, shows that oxygen and silicon make up the major portion. These elements are, of course, found in chemical combination with others, but nearly half the weight is oxygen, while more than a quarter is silicon. Silicon, iron, aluminum, and magnesium exist in large quantities, the proportions being about 46 per cent oxygen, 27 per cent silicon, 8 per cent aluminum, 5 per cent iron, 4 per cent calcium, and 3 per cent potassium, other elements making up the remainder. Almost all the minerals are found in combination with others, the rough material being known as ores, and from these the single mineral or metal must be extracted. Gem stones are not extracted, except by simple separation, from ores. They are found as we know them, with the exception of shaping and polishing which has been applied to improve their beauty.

At present, about 92 different stable elements are known, and all minerals are composed of one or more of these elements. For conciseness, these elements are generally denoted by a symbol, e.g. C for carbon, Al for aluminum, Mg for magnesium, and the chemist has a simple means of showing not only the constituent elements of a substance by such symbols but also their compara tive weights.
Elements combine in definite proportions only, and each proportion is a definite character of that element, which is called its atomic weight. For instance, the atomic weight of hydrogen is 1, of carbon 12, of oxygen 16, and of magnesium 24. Certain gases and substances are capable of forming acids in conjunction with hydrogen, or hydrogen and oxygen. These acids combine with greater or less avidity with other elements which do not form acids, and which are termed bases. Such a combination of an acid with a base produces a compound solution called a salt. All the salts whose names terminate in “ide,” such as fluorides, sulphides, etc., are simply combinations of a non-metallic element with a metal.