For the purpose of presenting all that is connected with that precious metal, that has built up a state within a few years, and of making the reader fully acquainted with all that is necessary for the gold-seeker to know, we will now describe, in some detail, the natural history, character of gold, and the mode of determining its presence and value.
Gold invariably exhibits something of the peculiar yellow color which it is known to possess in a pure state; but this color is modified by various metals with which it may be mixed. Thus it may be described as having various shades of gold-yellow; occasionally approaching silver-white, occasionally resembling brass-yellow of every degree of intensity, and even verging on steel-gray in some specimens from South America.
The lustre of gold is highly metallic and shining, and owing to the small amount of oxidation at its surface, it preserves its shining lustre even after long exposure in contact with other substances. Thus the shining particles are often seen in sand when the quantity is barely sufficient to repay the cost of working, notwithstanding the value of the metal. Even however, if the surface is dull, the true color and appearance are easily restored by rubbing, and when polished it takes a very vivid lustre, which is preserved for a long time in the atmosphere.
Although in the division which has been introduced into gold-yellow, brass-yellow, and grayish-yellow, native gold seems with some slight modifications to agree with the geological relations of its varieties, yet this mode of arrangement deserves little serious notice. The gold-yellow varieties comprise the specimens of the highest gold-yellow colors, though there are some among them which have rather a pale color; they include most of the crystals and of the imitative shapes, in fact the greater part of the species itself. The brass-yellow native gold is confined to some of the regular and imitative shapes of a pale color (which is generally called brass-yellow,) and, as it is said, of a less specific gravity than the preceding one; but this does not seem to have ever been ascertained by direct experiment. The grayish-yellow native gold occurs only in those small flat grains which are mixed with the native platina, and possess a yellow color a little inclining to gray; they are said to have the greatest specific gravity of them all. The real foundation of this distribution seems to be the opinion that the first are the purest, the second mixed with a little silver, and the third with platina. It is not known whether the latter admixture really takes place, but it is certain that several varieties of gold-yellow native gold contain an admixture of silver.[17]
In color and lustre, inexperienced persons might mistake various substances for gold; these are chiefly iron and copper pyrites, but from them it may be readily distinguished, being softer than steel and very malleable; whereas iron pyrites is harder than steel, and copper pyrites is not malleable; for although the latter mineral yields easily to the point of a knife, it crumbles when we attempt to cut or hammer it, whereas gold may be separated in thin slices, or beaten out into thin plates by the hammer. There can thus be no possible difficulty in distinguishing these various minerals in a native state, even with nothing but an ordinary steel knife. From any other minerals, as mica, whose presence has also misled some persons, gold is easily known by very simple experiments with a pair of scales, or even by careful washing with water, for gold being much heavier than any other substance found with it (except platina and one or two extremely rare metals,) will always fall first to the bottom, if shaken in water with mud, while mica will generally be the last material to fall. This is the case, however fine or few the particles of either mineral may be.
Gold therefore can be distinguished by its relative weight or specific gravity, and by its relative hardness, from other bodies which resemble it. It is described generally as soft, completely malleable and flexible, but more accurately as softer than iron, copper or silver, but harder than tin or lead. It is useful to know facts of this kind, as a simple experiment that can be made with instruments at hand, is often more valuable than a much more accurate examination requiring materials not immediately available. Thus if it is found that a specimen (perhaps a small scale or spangle) is readily scratched by silver, copper or iron, and scratches tin and lead, it may, if of the right color and sinking rapidly in water, be fairly assumed to be gold.
The weight of gold, as of all substances, it is convenient to estimate relatively, and in comparison with the weight of an equal volume of water. The relative weight, or specific gravity, as it is called, of gold, is remarkably high, the lightest varieties being twelve times heavier than water, and pure gold nineteen times. This is expressed by saying that the specific gravity of native gold is 12-19, and the number determined by comparing the weight of the mineral in water and air.
As the value of gold depends almost entirely on its specific gravity, and this test, therefore, is of the greatest practical importance, it will not be out of place if we here explain some very simple apparatus for the determination of this point.
If the specimen then is large enough to be suspended conveniently by a thread, weigh it first in air by a fine balance, expressing the result in grains, and taking care previously to remove dust or loosely adhering particles. Then suspend it by a horsehair from the scale-pan (it is convenient to have a hook attached to it for this purpose,) and thus suspended, immerse it and re-weigh it in water, taking care that it is covered on all sides by at least half an inch of water, and carefully brushing off with a feather any bubbles of air that adhere to the surface. The results may then be noted as follows:—
| Weight of substance in the air in grains | |
| Deduct weight of ditto in water | |
| Difference |