“Fig. 21. Crystal of transparent quartz or “rock crystal,” frequently called a “diamond” in the mining districts, as “Bristol diamond,” a “Cornish diamond,” &c. The crystal represented by this figure was brought from California by a person who refused 200l. for it, under the impression that it was a real diamond, because it scratched glass and could not be scratched with a file. Its real value, however, is not more than 2s. 6d.
“Fig. 22. Beryl, presents a six-sided prism, and is usually of a green colour.”
River pearls, to find.
When substances are found which are supposed to be precious stones, the file test should be at once applied; if the teeth of the instrument “bite,” as it is called, or cut into the substance, it will be at once fair to infer that some inferior mineral has been discovered. The bit of sapphire from the case may also be called into use, and if the stone you have found is of white colour, and a corner of your sapphire bites or scratches it, there is no hope of its being a diamond. If on weighing it the specific gravity of the specimen is found to be less than 3·9, it will not turn out to be a ruby or sapphire. The application of heat is another test, as if no electricity is manifested it will not turn out to be a gargoon or a topaz. If, on testing it on your piece of flint glass, the surface of that is bitten by the specimen, it will probably be found to be either rock crystal, quartz, or perchance beryl. The rivers of many countries, our own amongst the number, not unfrequently contain large mussel-like shells; these are the fresh-water pearl mussels (Unio margaritiferus), and the pearls which these at times contain are of considerable value, and well repay being looked for when the rivers are low.
“All is not gold that glitters.” Sulphuret of iron and yellow mica are not unfrequently mistaken by the inexperienced for gold, and we have not unfrequently had some little difficulty in convincing the sanguine discoverer of his error. Sulphuret of iron, pyrites, or the mundic of the miners, is a bright yellow glittering mineral, which sometimes has gold associated with it. The differences between it and gold are sufficiently marked. Strike the suspected fragment on a hard substance with a hammer, and if “mundic,” it at once becomes reduced to minute fragments, whilst gold would be only slightly flattened. Gold is malleable; mundic is not. Gold can be cut with the pocket-knife just as easily as copper; mundic resists the knife, turns its edge, and will strike fire against its back, giving out sulphurous fumes. Mundic, after being made red hot, is attracted by the magnet; gold never is. Hot nitric acid causes it to decompose with much effervescence, leaving such spangles of gold as it may contain free in the bottom of the test tube. Gold dust is readily taken up by quicksilver; mundic is not. Yellow mica is so much lighter than gold that its comparative want of ponderability should at once distinguish it; a small portion placed on an iron bar, and heated in the fire to redness becomes, on cooling, flakey and lustreless, whilst gold would remain unaltered; it floats on the surface of mercury, refusing to unite with it, whilst gold is immediately converted into an amalgam. Sulphuret of copper, or copper ore as it is usually called, breaks freely under the hammer, but can be cut easily with the knife, only instead of producing a solid metallic chip it crumbles into powder, just as soft stone or chalk would. Alluvial tin can in no case be mistaken for either gold, silver, or copper. It is dark coloured, breaks into powder under the hammer, and is exceedingly ponderous. With the so-called rosin and wood tin we cannot deal here, as the explorer is not very likely to find them. Minute fragments of stream tin are to be easily distinguished from small bits of iron ore by first heating them red hot, and then subjecting them to the magnet; iron will be attracted, tin will not.
Iron ore, to smelt.
Many wild countries produce iron ore of remarkable purity, and a number of native tribes, by a rough system of smelting, contrive to obtain enough metal for the manufacture of their weapons, implements, &c. The greater the purity of the metal, the less difficulty will be experienced in dealing with it. Should the explorer at any time be called on to smelt a little iron ore, he may proceed as follows: Build a turret-shaped furnace, proportioned to the quantity of ore to be treated, line it with ant-hill clay, or common clay and sand, leaving a hole in the front near the bottom, which has a temporary stopper of clay placed in it, and another orifice about 2ft. up the back for the air blast to enter at. Either a large pair of double bellows, compressible skin air-bags, such as we have before described, or blowing cylinders, such as are represented in the annexed [illustration], must be set up at a convenient distance from the back of the furnace. These cylinders are used by the inhabitants of New Guinea instead of bellows, and answer remarkably well. They are composed of two hollow tree trunks, placed side by side; a wooden tube, which serves to let the air out, unites them; and a man or boy sits on the tops of the tubes, and works alternately up and down a couple of mop-shaped pistons, which are made from poles armed at the ends with bundles of fibre, feathers, or dry grass, so adjusted that they expand on being thrust down and collapse on being drawn up. As one piston man gets fatigued, another takes his place; thus a continuous stream of air is kept up. Whatever method of blast is decided on, it must be so arranged as to be continuous and powerful. When the interior of the furnace is quite dry, throw in a good quantity of well-burned charcoal; then a layer of split dry wood until it reaches about 1ft. above the entrance of the blast; then another layer of charcoal and dry cow dung a few inches deep; then sprinkle in loosely a layer of broken iron ore, mixed with a little limestone if you can get it; then another layer of charcoal and dry cow dung, and another of ore; and so on until the furnace is all but full, only one layer of wood being used. Now through the blast entrance introduce some well-ignited and glowing embers from your fire; put in the tube of your blast, which may be of baked clay; lute it fast in its place, so as to prevent any escape of air; and proceed to blow, when your furnace will soon be in a state of active ignition and glow. Keep up the blast steadily, and as the contents of the furnace sink down add to them from above layer by layer as before directed, until it is considered that enough metal has been cast in. So soon as it is thought probable that the iron has melted, a small portion of the clay of the tap-hole may be removed with an iron bar, when, if in a sufficiently fluxed condition, the iron will run freely out into long shallow pits dug to receive it. The iron thus procured is called bloom, and has to be heated in pieces in the forge fire, and thoroughly roasted and thumped about until it is soft and tough enough for general use. The natives do not as a rule wait for their iron to flow, but open the furnace when it cools down, and then drag out such bloom as may have settled to the bottom. Excellent steel is made from iron thus procured by the natives of the hill districts of India, by putting it in small earthen crucibles with charcoal, rice, chaff, peroxide of manganese, and green leaves. These pots are then luted down with clay, and placed in a clay furnace heated with dry cow dung and charcoal. Here they remain for a considerable time, when the fire is allowed to burn out; the pots are then, when cool, removed, and the steel taken out to be fashioned by the hand of the smith into any form required. We have used a great deal of both iron and steel prepared as above described, and found both of admirable quality.
Chemical tests for minerals.