When a piece of gold is broken (which is not done without difficulty—greater in proportion to its purity,) the fractured edges are very uneven and torn, exhibiting a peculiar fibrous appearance, known to mineralogists as "fine hackly." This fracture indicates that the mineral is torn asunder and not really broken, and is a proof of considerable toughness.
The form in which gold is found is various. It is sometimes crystalline, in eight or twelve-sided regular figures, passing into cubes, but the crystals are generally small and rare. In case of such crystals being found, it is well worth knowing that they possess a value as mineral specimens far beyond that of the gold which they contain.
More frequently the metal is found in lumps or grains, called by the Spaniards pepitas, varying in size from that of a pin's head to masses weighing, as has been already mentioned, nearly one hundred pounds troy. The term pepita is only applied to grains of some magnitude, and the most common limits of size are from that of a small pin's head to that of a nut or gooseberry.
When much smaller and still rounded, they are called gold dust, and when flattened, scales or spangles. In nature, and when seen in veins of quartz, gold often occurs foliated, or in leafy expansions of extreme thinness, or in branchy (dendritic) forms, probably made up of minute crystals. It is in the form of very minute grains that the metal is generally disseminated through rocks and auriferous ores of various metals, and these are reduced according to circumstances in methods that will be alluded to in a future chapter. In pepitas and small grains it is carried down by streams and deposited in their beds, the pepitas being usually most abundant where there is reason to suppose considerable disintegration of the surface, and where the action of denuding causes to a great extent is evident. The coast of Africa and the rivers of Europe are examples of the former case, while the Siberian deposits and those of California would appear to belong to the latter.
The following are examples of the constituent parts of various specimens of gold obtained from different gold districts, and will form a useful guide for comparison.
Table showing the Composition of Native Gold.[19]
| Locality. | Gold. | Silver. | Copper. | Iron. |
| Auriferous sand of Schabrowski, near Katherinenburg, Siberia (G. Rose) | 98·76 | 0·16 | 0·35 | 0·06 |
| Boruschka, near Nijny-Tagilsk, Siberia (Rose) | 94·41 | 5·23 | 0·39 | 0·04 |
| Brazil (Darcet) | 94·00 | 6·85 | ||
| Beresovsk, Siberia (Rose) | 93·78 | 5·94 | 0·08 | |
| Sand near Miask, Siberia (Rose) | 92·47 | 7·27 | 0·06 | 0·08 |
| Bogota (Boussingault) | 92·00 | 8·00 | ||
| Washings near Miask, Siberia (Rose) | 89·35 | 10·65 | ||
| Gold of Senegal (Darcet) | 86·97 | 10·53 | ||
| Auriferous sand, Nijny-Tagilsk, Siberia (Rose) | 83·85 | 16·15 | ||
| Trinidad gold, (Boussingault) | 82·40 | 17·60 | ||
| Transylvanian gold (Ditto) | 64·52 | 35·48 | ||
| Mine of Sinarowski in the Altai (Rose) | 60·08 | 38·38 | 0·33 |
The gold from California, according to the assay of Mr. Warwick of New York, yields 89·58 per cent, pure gold, and is therefore, about equal to that obtained from the washings of Miask (the richest district in Western Siberia, and that producing the largest pepitas,) and superior, as the assayer remarks, to the gold dust from Senegal.
There is a remarkable mixture of native gold with silver occasionally found in Siberia, and known under the name of electrum. Its color is pale brass-yellow, passing into silver-white. It occurs in small plates and imperfect cubes, and possesses many of the characters of gold, but it consists only of 64 per cent. of that metal, and 36 per cent. silver. It is at once known by its low specific gravity, which does not exceed 12.
Other mixtures of gold are (1) a rhodium-gold found in Mexico, and containing 34 to 43 per cent. of rhodium, having a specific gravity of 15½—16·8, and a clear, dirty yellow color; and (2) a palladium-gold (containing 9·85 per cent. palladium, and 4·17 per cent. silver) found in Brazil and elsewhere in South America, in small crystalline grains of pale yellow color. The auriferous ores of tellurium, including silver, have hitherto only been found in Transylvania. Their color is steel-gray, and they tarnish on exposure. The variety called graphic-gold, or graphic tellurium, consists of about 60 per cent. of tellurium, 30 per cent. gold, and 10 per cent. silver, and is worked chiefly as an ore of gold. Another variety, "yellow gold glance," yields somewhat less tellurium, gold and silver, and as much as 20 per cent. of lead.