FROM NATURE’S WORKSHOP

Hawera Star, Volume XLV, 17 October 1925, Page 13

FROM NATURE’S WORKSHOP

CURIOUS fact about the majority of precious stones is that they are merely crystalline forms of extremely common substances. If we consider the chief gems to be, say, the diamond, ruby, sapphire, emerald, pearl, topaz, turquoise, and opal, 1 we find that only in turquoise and . emerald are the substances themselves rare, considered as chemical compounds, and even in these two eases the rarity is by no means great. But the crystalline forms of the common compounds, fashioned into jewels in nature’s laboratory, are rare indeed.

Take, for example, the case of the diamond, most highly esteemed of all stones. Colourless itself, yet sparkling with every colour of the rainbow, it is surely made of rare ingredients. But no! The finest diamond that ever existed was composed of nothing but carbon, exactly the same in composition as the soot in a dirty chimney or the “ blaeklead ” which polishes a stove. Only because of its crystalline form does the diamond have properties different from the properties of those humble brothers.

What, then, is a crystal, that it should be so different? We may define a crystal as a naturally occurring substance which has a definite geometrical shape externally and a definite arrangement of its internal particles. Suppose that we had a large cubical box, perhaps of one foot side, and we desired to fill it with small one-inch cubes. We might throw the cubes into the box in a haphazard fashion, or we might pack them regularly in rows. A crystal is like the box with the cubes inside regularly arranged. . A piece of glass, cut into a crystal shape, is like the box with the haphazard arrangement: its internal structure is entirely without symmetery, so that when broken it breaks irregularly. A crystal, on the other hand, always breaks along the lines of divison or “grain” of its particles, and thus has definite lines of cleavage.

Since man knows quite well how to make crystals in the laboratory, it was inevitable that man should attempt to make diamonds. Moreover, he succeeded. The usual plan for making crystals of any substance is to dissolve it in a suitable solvent and concentrate the solution. Crystals will appear when the' right degree of concentration is reached. The French scientist Mois; san dissolved lampblack in molten iron, subjected the solution to great pressure, and found that the carbon was deposited in the form of diamonds. They were extremely minute, but there was no doubt about their .nature. It is not ,nt all unlikely that Moissan copied nature’s method of manufacture. Natural diamonds are found in a clay, technically known as “blue clay,” which is extremely rich in iron, and which occurs in “pipes” which have risen through the surface rock from the depths below as the result of enormous underlying pressure. It is quite probable therefore that carbon from*some deep-down coal scam has been dissolved by a sill of molten or plastic iron ore, and the latter has then been thrust up by a pressure so great that it formed the dissolved carbon into diamonds. Moissan’s manufactured diamonds were small only because he could not get sufficient pressure to imitate exactly the earth’s action. The largest jiatural diamond ever found was the Cullinan, obtained from the Premier mine near Pretoria, South Africa. In the rough, this stone weighed no less than one and a third pounds!

GEMS OF THE EARTH

FASHIONED FROM COMMON MATERIALS.

Another example of the value, of crystalisation to a common compound is afforded by the ruby and the sapphire. These gems are nothing but oxide of aluminium, coloured by a trace of impurity. Yet oxide of aluminium is one of tire chief constituents of common clay, in which it occurs combined with silica. Artificial rubies and sapphires are made quite easily and rapidly from" ordinary powdered alum, and ii l this case the process is highly successful from a commercial point of view, for the resulting stones are not only large, but are indistinguishable by any tost whatever from those won from the earth.

Topaz gets even nearer to clay than do the ruby and sapphire, for topaz is silicate of aluminium—that is, oxide of aluminium, plus silica in combination. Opal, which is composed of silica, is not a crystalline substance; its play of colours is due to a different structure. Silica is, of course, very common; literally every pebble on the beach is composed, almost without exception, of silica. But in the case of opal the silica has been deposited while Ifot, and in cooling the contraction has caused the formation of , innumerable cracks, so that the stone has split into very thin layers. ’The cracks between the filmy layers have afterwards become filled with more silica, deposited from solution and o£ somewhat different density from the original. As a result of interference with the light waves tjhesc thin layers of different densities give the beautiful, apparently deep-seated colour effect for which the opal is famous. It is interesting to note that the finest white opal and the best black opal in

the world both come from New South Wales, the former from White Cliffs and the latter from Lightning Ridge. The dark tint of the black'opal is due to the presence of iron.

Emerald consists of silicate of aluminium (again the clay constituents) combined with a compound of the somewhat rare element, beryllium. This element is closely allied to the common ipetals magnesium and calcium. An extremely beautiful stone may be made

by crystallising a silicate of aluminium and magnesium; it is, of course, not an omorald, but it is by no moans a bad substitute.

The remaining gom, turquoise, is peculiar in that it is opaque.: -Its. composition is somewhat complicated, being a phosphate of- iron, copper, and aluminium. For massed . ornamentation turquoise gives a beautiful effect; but as a single gem it is more or less over shadowed by its transparent sisters.

CANADIAN FURS . -.: :;. \ A collection of furs"just' coiripleted at the Canadian Pavilion at Wembley comprises the skins of all the 34 furbeating animals found in Canada. There are some very fine skins on View, including one of a cream raccoon; the first which has been known in. the fur trade for 400 years. All the skins of the 34 animals shown can be put to commercial use, and the furs shown are worth approximately £4OOO.