Amber has from the most remote ages been familiar to humanity, ornaments in this material having come down to us, shaped by men of the Stone Age, thus proving its antiquity.

Many fanciful theories were given in bygone days with regard to its origin, amongst others the historian Nicias stating that the heat of the Sun was so great in some regions as to set up intense perspiration in the earth, from which Amber resulted ; whilst among the Greeks a legend existed that it originated in the tears of the sisters of Phaethon, who, in their sorrow at his death, were turned into popular trees, and whose perpetual tears congealed into Amber. Pliny asserted it to be the overflowing sap of certain trees, hence the name Succinum, from a word signifying “juice” ; and modern research confirms this idea of a vegetable origin, for Amber is now known to be the fossil resin of an extinct species of pine of the Tertiary Period.

Amber is found in large quantities on the coast of the Baltic, washed up after storms, and the German Government exercises a strict monopoly over the trade. It is also found round the coasts of Denmark, Norway, Sweden, and parts of Asia and the United States ; and in Essex, Suffolk, and Norfolk. It is very light and soft, possessing remarkable electric properties when heated.

That it was once in a liquid state is shown by the insects and plants sometimes found in it, a good many of the insects belonging to species that no longer exist. These specimens specially attracted the attention of the Romans and doubtless gave Pliny his idea of its origin.

Great quantities were introduced into Rome during the reign of the Emperor Nero, who in verse described the hair of his wife as amber coloured, causing much emulation amongst the ladies of his court in their endeavours to secure the fashionable colour. The name Amuletum was given to Amber as well as to the flower Cyclamen, both having the power to protect from poisonous drugs, necklaces being worn specially by children for this purpose, and also as a counter-charm against witchcraft and sorcery.

Its range of medicinal virtues is very extensive, Callistratus asserting it to be of great service at any period of life against insanity, either taken as a powder, or worn round the neck ; the golden yellow variety known as the Chryselutum being specially used to ward off ague. The Rev. C. W. King says that ” the wearing of an Amber necklace has been known to prevent the attacks of erysipelas in a person subject to them, which has been proved by repeated experiments beyond all possibility of doubt.

Its action here cannot be explained, but its efficacy as a defender of the throat against chills is evidently due to its extreme warmth when in contact with the skin, and the circle of electricity so maintained, which latter may account for its remedial agency in the instance quoted above.” He also says : “In Pliny’s time amber was universally worn as necklaces by the Transpadane females of Lombardy and Piedmont, partly as an ornament and partly as a prophylactic against goitres, to which they were subject in consequence of the hard quality of the water they drank.”

Amber was also worn to protect from deafness, digestive troubles, catarrh, jaundice, loss of teeth from looseness, and as a child’s amulet against convulsions when teething.

Its popularity as mouth-pieces to pipes, cigar and cigarette-holders arose from a belief in the East that Amber will not transmit infection. It has ever been in vogue throughout China, Japan, India, and the East, and retains its favour to the present day.

The Chinese use it extensively in incense, and it is also used in the manufacture of various perfumes and medical compounds.

This is a safe and very common method of proving a stone, since its specific gravity does not vary more than a point or so in different specimens of the same stone.

There are several ways of arriving at this, such as by weighing in balances in the usual manner, by displacement, and by immersion in liquids the specific gravity of which are known.

Cork is of less specific gravity than water, therefore it floats on the surface of that liquid, whereas iron, being heavier, sinks. So that by changing the liquid to one lighter than cork, the cork will sink in it as does iron in water; in the second instance, if we change the liquid to one heavier than iron, the iron will float on it as does cork on water, and exactly as an ordinary flat-iron will float on quicksilver, bobbing up and down like a cork in a tumbler of water.

If, therefore, solutions of known but varying densities are compounded, it is possible to tell almost to exactitude the specific gravity of any stone dropped into them, by the position they assume.

Thus, if we take a solution of pure methylene iodide, which has a specific gravity of 3.2981, and into this drop a few stones selected indiscriminately, the effect will be curious: first, some will sink plump to the bottom like lead; second, some will fall so far quickly, then remain for a considerable time fairly stationary; third, some will sink very slowly; fourth, some will be partially immersed, that is, a portion of their substance being above the surface of the liquid and a portion covered by it; fifth, some will float on the surface without any apparent immersion. In the first case, the stones will be much heavier than 3.2981; in the second, the stones will be about 3.50; in the third and fourth instances, the stones will be about the same specific gravity as the liquid, whilst in the fifth, they will be much lighter, and thus a rough but tolerably accurate isolation may be made.

On certain stones being extracted and placed in other liquids of lighter or denser specific gravity, as the case may be, their proper classification may easily be arrived at, and if the results are checked by actual weight, in a specific gravity balance, they will be found to be fairly accurate.

The solution commonly used for the heaviest stones is a mixture of nitrate of thallium and nitrate of silver. This double nitrate has a specific gravity of 4.7963, therefore such a stone as zircon, which is the heaviest known, will float in it. For use, the mixture should be slightly warmed till it runs thin and clear; this is necessary, because at 60° (taking this as ordinary atmospheric temperature) it is a stiff mass. A lighter liquid is a mixture of iodide of mercury in iodide of potassium, but this is such an extremely corrosive and dangerous mixture, that the more common solution is one in which methylene iodide is saturated with a mixture of iodoform until it shows a specific gravity of 3.601; and by using the methylene iodide alone, in its pure state, it having a specific gravity of 3.2981, the stones to that weight can be isolated, and by diluting this with benzole, its weight can be brought down to that of the benzole itself, as in the case of Sonstadt’s solution.

This solution, in full standard strength, has a specific gravity of 3.1789, but may be weakened by the addition of distilled water in varying proportions till the weight becomes almost that of water.

Knowing the specific gravity of all stones, and dividing them into six groups, by taking a series of standard solutions selected from one or other of the above, and of known specific gravity, we can judge with accuracy if any stone is what it is supposed to be, and classify it correctly by its mere floating or sinking when placed in these liquids.

Remembering our lessons in physics we recall that just as light-rays may be refracted, absorbed, or reflected, according to the media through which they are caused to pass, so do heat-rays possess similar properties.

Therefore, if heat-rays are projected through precious stones, or brought to bear on them in some other manner than by simple projection, they will be refracted, absorbed, or reflected by the stones in the same manner as if they were light-rays, and just as certain stones allow light to pass through their substance, whilst others are opaque, so do some stones offer no resistance to the passage of heat-rays, but allow them free movement through the substance, whilst, in other cases, no passage of heat is possible, the stones being as opaque to heat as to light. Indeed, the properties of light and heat are in many ways identical, though the test by heat must in all cases give place to that by light, which latter is by far of the greater importance in the judging and isolation of precious stones.

It will readily be understood that in the spectrum the outer or extreme light-rays at each side are more or less bent or diverted, but those nearest the centre are comparatively straight, so that, as before remarked, these central rays are taken as being the standard of light-value.

This divergence or refraction is greater in some stones than in others, and to it the diamond, as an example, owes its chief charm. In just such manner do certain stones refract, absorb, or reflect heat; thus amber, gypsum, and the like, are practically opaque to heat-rays, in contrast with those of the nature of fluorspar, rock-salt, etc., which are receptive.

Heat passes through these as easily as does light through a diamond, such stones being classed as diathermal (to heat through). So that all diathermal stones are easily permeable by radiant heat, which passes through them exactly as does light through transparent bodies.

Others, again, are both single and double refracting to heat-rays, and it is interesting to note the heat-penetrating value as compared with the refractive indexes of the stone. In the following table will be found the refractive indexes of a selection of single and double refractive stones, the figures for “Light” being taken from a standard list.

The second column shows the refractive power of heat, applied to the actual stones, and consisting of a fine pencil blowpipe-flame, one line (the one twelfth part of an inch) in length in each case.
This list must be taken as approximate, since in many instances the test has been made on one stone only, without possibility of obtaining an average; and as stones vary considerably, the figures may be raised or lowered slightly, or perhaps even changed in class, because in some stones the least stain or impurity may cause the heat effects to be altered greatly in their character, and even to become singly or doubly refracting, opaque or transparent, to heat-rays, according to the nature of the impurity or to some slight change in the crystalline structure, and so on.

Selection of Singly refracting stones. Indexes of Rays of
Light. Heat.

Fluorspar 1.436 4.10 varies
Opal 1.479 2.10 ”
Spinel 1.726 1.00
Almandine 1.764 1.00
Diamond 2.431 6.11 double

Selection of Doubly refracting stones. Indexes of Rays of
Light. Heat.

Quartz 1.545 4.7 single and double
Beryl 1.575 1.0 varies considerably
Topaz 1.635 4.1 ” ”
Chrysoberyl 1.765 1.1 ” ”
Ruby 1.949 5.1 single and double

The tourmaline has a light-refractive index of 1.63, with a heat index of none, being to heat-rays completely opaque.

The refractive index of gypsum is 1.54, but heat none, being opaque.

The refractive index of amber is 1.51, but heat none, being opaque.

In some of the specimens the gypsum showed a heat-penetration index of 0.001, and amber of 0.056, but mostly not within the third point.

In all cases the heat-penetration and refraction were shown by electric recorders. These figures are the average of those obtained from tests made in some cases on several stones of the same kind, and also on isolated specimens. Not only does the power of the stone to conduct heat vary in different stones of the same kind or variety, as already explained, but there is seen a remarkable difference in value, according to the spot on which the heat is applied, so that on one stone there is often seen a conductivity varying between 0.15 to 4.70.

This is owing to the differences of expansion due to the temporary disturbance of its crystalline structure, brought about by the applied heat. This will be evident when heat is applied on the axes of the crystal, on their faces, angles, lines of symmetry, etc., etc., each one of which gives different results, not only as to value in conductivity, but a result which varies in a curious degree, out of all proportion to the heat applied.

In many cases a slight diminution in applied heat gives a greater conductivity, whilst in others a slight rise in the temperature of the heat destroys its conductivity altogether, and renders the stone quite opaque to heat-rays.

This anomaly is due entirely to the alteration of crystalline structure, which, in the one case, is so changed by the diminution in heat as to cause the crystals to be so placed that they become diathermal, or transparent to heat-rays; whilst, in the other instance, the crystals which so arrange themselves as to be diathermal are, by a slightly increased temperature, somewhat displaced, and reflect, or otherwise oppose the direct passage of heat-rays, which, at the lower temperature, obtained free passage.

Thus certain stones become both opaque and diathermal, and as the heat is caused to vary, so do they show the complete gamut between the two extremes of total opacity and complete transparency to heat-rays.

For the purpose under consideration, the temperature of the pencil of heat applied to the stones in their several portions was kept constant. It will be seen, therefore, that no great reliance can be placed on the heat test as applied to precious stones.

Jet 1.348
Amber 1.000

Many stones are capable of exhibiting the same phenomenon, not only by friction, as in Thales’s experiment, but also under the influence of light, heat, magnetism, chemical action, pressure, etc., and of holding or retaining this induced or added power for a long or short period, according to conditions and environment.

If a small pith ball is suspended from a non-conducting support, it forms a simple and ready means of testing the electricity in a stone. According to whether the ball is repelled or attracted, so is the electricity in the stone made evident, though the electroscope gives the better results.

By either of these methods it will be found that some of the stones are more capable of giving and receiving charges of electricity than are others; also that some are charged throughout with one kind only, either positive or negative, whilst others have both, becoming polarised electrically, having one portion of their substance negative, the other positive. For instance, amber, as is well known, produces negative electricity under the influence of friction, but in almost all cut stones, other than amber, the electricity produced by the same means is positive, whereas in the uncut stones the electricity is negative, with the exception of the diamond, in which the electricity is positive.

When heated, some stones lose their electricity; others develop it, others have it reversed, the positive becoming negative and vice versâ; others again, when heated, become powerfully magnetic and assume strong polarity.

When electricity develops under the influence of heat, or is in any way connected with a rising or falling of temperature in a body, it is called “pyro-electricity,” from the Greek word “pyros,” fire. The phenomenon was first discovered in the tourmaline, and it is observed, speaking broadly, only in those minerals which are hemimorphic, that is, where the crystals have different planes or faces at their two ends, examples of which are seen in such crystals as those of axinite, boracite, smithsonite, topaz, etc., all of which are hemimorphic.

Taking the tourmaline as an example of the pyro-electric minerals, we find that when this is heated to between 50° F. and 300° F. it assumes electric polarity, becoming electrified positively at one end or pole and negatively at the opposite pole. If it is suspended on a silken thread from a glass rod or other non-conducting support in a similar manner to the pith ball, the tourmaline will be found to have become an excellent magnet.

By testing this continually as it cools there will soon be perceived a point which is of extreme delicacy of temperature, where the magnetic properties are almost in abeyance. But as the tourmaline cools yet further, though but a fraction of a degree, the magnetic properties change; the positive pole becomes the negative, the negative having changed to the positive.

It is also interesting to note that if the tourmaline is not warmed so high as to reach a temperature of 50° F., or is heated so strongly as to exceed more than a few degrees above 300° F., then these magnetic properties do not appear, as no polarity is present. This polarity, or the presence of positive and negative electricity in one stone, may be strikingly illustrated in a very simple manner: -If a little sulphur and red-lead, both in fine powder, are shaken up together in a paper or similar bag, the moderate friction of particle against particle electrifies both; one negatively, the other positively.

If, then, a little of this now golden-coloured mixture is gently dusted over the surface of the tourmaline or other stone possessing electric polarity, a most interesting change is at once apparent. The red-lead separates itself from the sulphur and adheres to the negative portion of the stone, whilst the separated sulphur is at once attracted to the positive end, so that the golden-coloured mixture becomes slowly transformed into its two separate components -the brilliant yellow sulphur, and the equally brilliant red-lead. These particles form in lines and waves around the respective poles in beautiful symmetry, their positions corresponding with the directions of the lines of magnetic force, exactly as will iron filings round the two poles of a magnet.

From this it will clearly be seen how simple a matter it is to isolate the topaz, tourmaline, and all the pyro-electric stones from the non-pyro-electric, for science has not as yet been able to give to spurious stones these same electric properties, however excellent some imitations may be in other respects.

Further, almost all minerals lose their electricity rapidly on exposure to atmospheric influences, even to dry air; the diamond retains it somewhat longer than most stones, though the sapphire, topaz, and a few others retain it almost as long again as the diamond, and these electric properties are some of the tests which are used in the examination of precious stones.

Those stones which show electricity on the application of pressure are such as the fluorspar, calcite, and topaz.

With regard to magnetism, the actual cause of this is not yet known with certainty. It is, of course, a self-evident fact that the magnetic iron ore, which is a form of peroxide, commonly known as magnetite, or lodestone, has the power of attracting a magnet when swinging free, or of being attracted by a magnet, to account for which many plausible reasons have been advanced. Perhaps the most reasonable and acceptable of these is that this material contains molecules which have half their substance positively and the other half negatively magnetised.

Substances so composed, of which magnets are an example, may be made the means of magnetising other substances by friction, without they themselves suffering any loss; but it is not all substances that will respond to the magnet. For instance, common iron pyrites, FeS2, is unresponsive, whilst the magnetic pyrites, which varies from 5FeS, Fe2S3, to 6FeS, Fe2S3, and is a sulphide of iron, is responsive both positively and negatively. Bismuth and antimony also are inactive, whilst almost all minerals containing even a small percentage of iron will deflect the magnetic needle, at least under the influence of heat.

So that from the lodestone -the most powerfully magnetic mineral known -to those minerals possessing no magnetic action whatever, we have a long, graduated scale, in which many of the precious stones appear, those containing iron in their composition being more or less responsive, as already mentioned, and that either in their normal state, or when heated, and always to an extent depending on the quantity or percentage of iron they contain.

In this case, also, science has not as yet been able to introduce into an artificial stone the requisite quantity of iron to bring it the same analytically as the gem it is supposed to represent, without completely spoiling the colour. So that the behaviour of a stone in the presence of a magnet, to the degree to which it should or should not respond, is one of the important tests of a genuine stone.

Hardness. Specific Gravity.

Amber 2-1/2 1.000
Beryl 7-3/4 2.709-2.810
Chrysoberyl 8-1/2 3.689-3.752
Chrysolite 6-7 3.316-3.528
Corundum (the yellow variety
known as “Oriental Topaz”) 9 3.90-4.16
Diamond 10 3.502-3.564
Garnets (various) 6-1/2-7-1/2 3.4-4.5
Hyacinth (a form of Zircon) 7-1/2 4.7-4.88
Quartz (Citrine) 7 2.658
Sapphire 9 4.049-4.060
Spinel 8 .614-3.654
Topaz (for “Oriental Topaz,”) 8 3.500-3.520
Tourmaline 7-1/4 3.210

The garnet is usually in the form of a rhombic dodecahedron, or as a trisoctahedron (called also sometimes an icosatetrahedron), or a mixture of the two, though the stones appear in other cubic forms.

In hardness they vary from 6-1/2 to 8-1/2. They average from 40 to about 42 per cent. of silica, the other ingredients being in fairly constant and definite proportions. They are vitreous and resinous in their lustre and of great variety of colour, chiefly amongst reds, purples, violets, greens, yellows and blacks, according to the colouring matter present in their mass.

There are many varieties which are named in accordance with one or more of their constituents, the best known being:

(A) The iron-alumina garnet, having the formula 6FeO, 3SiO2 + 2Al2O3, 3SiO2. This is the “precious” garnet, or almandine, sometimes called the “Oriental” garnet; these stones are found in Great Britain, India, and South America, and are deep red and transparent, of vitreous lustre. They get up well, but certain varieties are so subject to defects in their substance, brought about by pressure, volcanic action, and other causes, some of which are not yet known, that their quality often becomes much depreciated in consequence. This inferior variety of the iron-alumina garnet is called the “common” garnet, and has little lustre, being sometimes opaque. The perfect qualities, or almandine, as described above, are favourite stones with jewellers, who mount great quantities of them.

The second variety is the (B) lime-iron garnet, formula, 6CaO,3SiO2 + 2Fe2O3,3SiO2. The chief of this class is the melanite, sometimes dull, yet often vitreous; it is mostly found in volcanic rocks, such as tuff; this variety is very popular with jewellers for mourning ornaments, for as it is a beautiful velvet-black in colour and quite opaque, it is pre-eminent for this purpose, being considerably less brittle than jet, though heavier. Another variety is the “topazolite,” both yellow and green. The “aplome” is greenish-yellow, yellowish-green, brown, and usually opaque. A further form of lime-iron garnet is the “pyreneite,” first found in the Pyrenees Mountains, hence its name.

The (C) lime-chrome garnets -6CaO,3SiO2 + 2Cr2O3, 3SiO2 – the chief of which is “uwarowite.” This is of a magnificent emerald green colour, translucent at edges and of a vitreous lustre. When heated on the borax bead it gives an equally beautiful green, which is, however, rather more inclined to chrome than emerald. This is an extremely rare stone in fine colour, though cloudy and imperfect specimens are often met with, but seldom are large stones found without flaws and of the pure colour, which rivals that of the emerald in beauty.

The fourth variety (D) is the lime-alumina garnet, its formula being -6CaO,3SiO2 + 2Al2O3,3SiO2. Like the others, it has a number of sub-varieties, the chief being the “cinnamon stone,” which is one of great beauty and value when perfect. This stone is almost always transparent when pure, which property is usually taken as one of the tests of its value, for the slightest admixture or presence of other substances cloud it, probably to opacity, in accordance with the quantity of impurity existent. This variety is composed of the oxides of aluminium and silicon with lime. In colour it ranges from a beautiful yellowish-orange deepening towards the red to a pure and beautiful red.

“Romanzovite” is another beautiful variety, the colour of which ranges through browns to black. Another important variety is the “succinite,” which gets up well and is a favourite with jewellers because of its beautiful, amber-like colour, without possessing any of the drawbacks of amber.

(E) The magnesia-alumina garnet -6MgO,3SiO2 + 2Al2O3,3SiO2 – is somewhat rare, the most frequently found being of a strong crimson colour and transparent. This variety is called “pyrope,” the deeper and richer tints being designated “carbuncle,” from the Latin carbunculus, a little coal, because when this beautiful variety of the “noble” garnet is held up between the eyes and the sun, it is no longer a deep, blood-red, but has exactly the appearance of a small piece of live or glowing coal, the scarlet portion of its colour-mixture being particularly evident.

The ancient Greeks called it anthrax, which name is sometimes used in medicine to-day with reference to the severe boil-like inflammation which, from its burning and redness, is called a carbuncle, though it is more usual to apply the word “anthrax” to the malignant cattle-disease which is occasionally passed on to man by means of wool, hair, blood-clots, etc., etc., and almost always ends fatally. A great deal of mystery and superstition has always existed in connexion with this stone – the invisibility of the bearer of the egg-carbuncle laid by a goldfinch, for instance.

(F) The manganese-alumina garnet -6MnO,3SiO2 + 2Al{2}O3,3SiO2 – is usually found in a crystalline or granular form, and mostly in granite and in the interstices of the plates, or laminæ, of rocks called schist. One variety of this, which is a deep hyacinth in colour, though often of a brown-tinted red, is called “spessartine,” or “spessartite,” from the district in which it is chiefly found, though its distribution is a fairly wide one.