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production from being followed to any great extent. Unliie most other materials of commerce, the formation of sulphur is still going forward wherever volcanic agency is in a state of activity. It appears to be sublimed by the subterranean heat through the crevices and fumeroles of the mountains; and this collects either as a slight efflorescent crust on the surface, or in crystals and in masses throughout the material of the ejected clays, ashes, &c. Speaking of the sulphur mountains of Iceland, Sir George Mackenzie says, "At the foot of an elevation, in a hollow formed by a bank of clay and sulphur, steam rushed with great force and noise from among the loose fragments of rock. Ascending still higher, we came to a ridge composed entirely of sulphur and clay, joining two summits of the mountain. Here we found a much greater quantity of sulphur than on any other part of tfce surface we had gone over. It formed a smooth crust, from a quarter of an inch to several inches in thickness: the crust was beautifully crystallised. Immediately beneath it we found a quantity of loose granular sulphur, which appeared to be collecting and crystallising as it was sublimed along with the steam. Sometimes we met with clay of different colours— white, red, and blue—under the crust; but we could not examine this place to any depth, as the moment the crust was removed, steam came forth, and proved extremely annoying. We found several pieces of wood, which were probably the remains of planks that had been formerly used in collecting the sulphur, small crystals of which partially covered them. There appears to be a constant sublimation of this substance, and were artificial chambers constructed for the reception and condensation of the vapours, much of it might probably be collected. As it is, there is a large quantity on the surface, and by digging, there is little doubt that great stores may be found." Such is the usual origin of native sulphur—a substance of greater commercial value to a country like llritain than the most of our readers may imagine. It is emploved for making gunpowder, sulphuric acid—which is indispensable to so many manufacturing processes—cinnabar, and for a variety of other purposes in the arts, as well as being used medicinally—requiring altogether an annual supply little short of 20,000 tons.
All our so-called " precious stones"—the diamond, ruby, emerald, amethyst, &c.—are but compounds of carbon, alumina, silica, lime, &c. and might therefore, so far as their mineralogical character is concerned, have been considered under the sections already presented. As none of them, however, occur in rocky masses, but rather as crystals, geodes, and concretions within other rocks, and as fashion has generally set a price upon them -wholly disproportioned to their utility, it may be as well to treat them as an independent class. Our limits will only permit us to mention a few of the more esteemed; seeing that lapidaries, jewellers, and others have vastly increased the nomenclature of precious stones hy giving individual names to specimens which are, in reality, but varieties of the same substance.
The most highly-prized of precious stones is the diamond, a crystalline mineral of unsurpassed lustre and hardness. It is the hardest known substance, and can be polished or cut only by its own dust or powder; hence the common saying of " diamond cut diamond." When perfectly pure, it is as transparent as a drop of the purest water, in which state it is known as a diamond of the first water; and in proportion as it falls short of this perfection, it is said to be of the second, third, or fourth water, till it becomes a coloured one. Coloured diamonds are generally yellow, blue, green, or red, and the higher the colour, the more valuable they are, though still inferior to those absolutely transparent. Diamond, as has been proved by numerous experiments, consists solely of carbon, being, in fact, a crystallised charcoal. Diamonds were originally discovered in Bengal, but they have since been found in other parts of India, in the East India islands, in the Brazils, and recently in the Ural Mountains. They occur chiefly in alluvial deposits of gravel and sand, lying in detached octohedral crystals, sometimes with plain, Dut more frequently with rounded surfaces. The finest are cut for ornamental purposes into brilliants, having curvilineal faces both at top and bottom; or into rose diamonds; that is, those having their tops or upper surfaces cut into a number of triangular facets, but quite flat beneath. The black, dirty, and flawy ones, and those unfit for being cut, are pulverised for the purpose of polishing others, besides being applied to various uses in the arts. Fractured portions, with good cutting edges, are usually set for glaziers' cutting pencils, in which state they are worth from twelve to twenty shillings. It is the ornamental diamonds that bring the exorbitant prices so frequently mentioned in moder n history, their value depending upon shape, colour, and purity, and being fixed at so much per carat of 3£ troy grains. "The largest diamond ever known was brought to the king of Portugal from Brazil. It is uncut, weighs 1680 grains, and its value is often quoted at £5,644,800. Similar extravagant valuations are applied to the famous Russian one weighing 195 carats; to that in the possession of the Great Mogul, weighing, cut, 280 carats; and to others; but it does not appear that any sum exceeding £150,000 has ever been given. The last great sale of jewels was in London in 1837, for the distribution of the Deccan booty, obtained by the army under the Marquis of Hastings. On that occasion the magnificent Nassau diamond, weighing 357J grains, of the purest water, brought only £7200." The Russian diamond, says another authority, is of the size of a pigeon's egg, and was purloined from a Brahminical idol by a French soldier; it passed through several hands, and was ultimately purchased by the Empress Catharine for the sum of £90,000, and an annuity of £4000. Perhaps the most perfect and beautiful diamond hitherto found is a brilliant brought from India by a gentleman of the name of Pitt, who sold it to the Regent, Duke of Orleans, for the sum of £100,000; its weight, 136 carats.
These may be conveniently grouped together as consisting essentially of crystallised alumina—traces of magnesia, silica, fluoric acid, chromic acid, &c. constituting the specific distinctions. The sapphire is of various colours—the blue being generally known among jewellers and lapidaries as the sapphire; the red, the Oriental ruby, and, next to the diamond, the most valuable of gems; and the yellow, the Oriental topaz. Corundum, or adamantine spar, is nearly allied to the sapphire, and, with the exception of the diamond, is the hardest substance known. It is almost a pure crystallised alumina, consisting of more than ninety per cent, of that substance, with a little silica and iron. It is found in India, China, and some parts of Europe; and is used in the East for the same purposes to which diamond powder is applied in England. Emery, so called from Cape Erneri, in the island of Naxos, is but a variety of corundum, with an admixture of iron, which gives to it a bluish-gray colour. From its extreme hardness, its powder is largely employed in the polishing of glass and metals, and in the cutting of gems and other minerals—all of which are abraded by it, with the exception of the diamond. The ruby, found chiefly in the sand of rivers in Ceylon, Pegu, and Mysore, is also of various colours—the scarlet-coloured being distinguished as spinelle ruby; the pale or rose-red, balass ruby; and the yellowish-red, rubieelle. The topaz likewise presents various shades between yellow and wine-colour; but, from its large per centage of silica, is harder than either of the preceding. The best varieties are known as the Brazilian, the Saxon, Siberian, and Scotch. The garnet, another well-known mineral, belongs to the same section, the varieties being essentially of alumina, with silica, magnesia, iron, &c. The most valuable is the precious garnet, almandine, or carbuncle, which is commonly a transparent, red, and beautiful mineral, either crystallised or in roundish grains. It is found in Ceylon, Pegu, and Greenland. The pyrope, a blood-red variety, found in Germany and Ceylon, is perfectly transparent, and, in roundish or angular grains, is perhaps next in value. The common garnet is not transparent like the preceding, and is most frequently of a dull-red or blackish-brown. It is found plentifully in Scotland, Sweden, and other countries where the primitive rocks abound; but comparatively few specimens are fit for the jeweller.
In these the predominant ingredient is silica; they may be called siliceous gems, just as the ruby and sapphire might be styled aluminous, or the diamond carbonaceous. The emerald is. one of the most esteemed, being of a beautiful green colour, and occurring in prismatic crystals. It consists essentially of silica, with a small per centage of alumina and glucina, the colouringmatter being oxide of chromium. The finest emeralds are brought from Peru and Brazil; the mines from which the ancients obtained their supply is said to have been in Upper Egypt. Beryl differs little from emerald except in colour—the latter name embracing the green varieties, the former all those that are tinged less or more with yellow or blue, or are altogether colourless. Beryls are found in Siberia, France, the United States, and in Brazil, the latter country furnishing the brilliant variety known as the precious beryl, or aqua-marine. Heliotrope, or bloodstone, is another common deep-green siliceous mineral, somewhat translucent, and often variegated with blood-red spots—whence its common appellation. Amethyst is a pure rock-crystal, of a.
furplish-violet colour, and of great brilliancy. It is found in udia, in Germany, Sweden, and Spain, but chiefly in Brazil, and is in great request for cutting into seals and brooches. "Some of the ancient vases and cups," says Brande, " are composed of this mineral, and it was an opinion among the Persians that wine drunk out of such cups would not intoxicate; hence its name from the Greek amethystos." The cairngorm of the lapidary is another crystallised quartz, of various hues, and nearly transparent. It derives its name from the mountain Cairngorm in Inverness-shire, and is much used as an ornamental stone in this country.
Agate, chalcedony, opal, carnelian, sardonyx, jasper, and some kindred substances, may be, without much impropriety, regarded as merely varieties of the same mineral, having different colours and degrees of transparency. They are found in most countries, and are used for seals, brooches, cameos, and other ornamental purposes—the larger geodes or mass being often fashioned into cups and vases. Carnelians and opals are perhaps the most valuable, some specimens of the Oriental opal being worth double the price of a sapphire of the same size. This variety is sometimes known as the Nonnius opal, from the senator Nonnius, the possessor of the famous opal of Rome, worth 20,000 sesterces, who preferred banishment to parting with it to Antony. The cat's-eye opal, so called from its presenting an effulgent pearly light like the changeable reflections of the eye of a cat, is another siliceous mineral or quartz, interspersed with filaments of asbestos. It is found chiefly in Ceylon and the Indian peninsula, and is held in great estimation among gem fanciers. When the late king of Candy's jewels were brought to the hammer in London in 1820, a specimen, which measured about two inches in diameter, brought upwards of £400.
Lapis-lazuli, or azure-stone, at one time held in the highest estimation, is another precious mineral, whose chief constituents are silica and alumina. Its principal localities are China, Persia, and Siberia, where it occurs in massive, but rarely in regular crystals. The finer specimens are prized by the lapidary; but by far the most important application of the substance is to the production of ultra-marine—a pigment which, till of late, was more precious than gold. Within these few years, however, the chemist has succeeded in producing an artificial ultra-marine possessing all the properties of the native pigment, and at such a rate, that several pounds weight can be procured for what, a dozen years ago, would scarcely have purchased a single ounce.
Several of the calcareous spars are of great beauty and transparency, but in general their softness and frangibility prevent them from being employed for ornamental purposes. Iceland spar, so called from the largest and most transparent specimens being found there, is a rhomboidal carbonate of lime, much used for experiments on the double refraction and polarisation of light. Fluor spar is a common mineral product, found in many places, but in great beauty and abundance in Derbyshire. It is a fluoride of calcium, occurring in crystals and in nodules of various colours, and often very prettily banded. The nodular specimens are occasionally worked into beads, brooches, and other ornamental purposes; but chiefly manufactured into vases, toiletboxes, jars, and such-like articles.
The preceding pages present but an imperfect outline of one of the most important and interesting subjects that can engage our attention. Important, as many of the arts depend wholly upon the production of the substances described; and interesting, as no intelligent mind can be indifferent to the origin and history of the mineral composition of our globe, or can fail to admire the ingenuity often displayed in bringing its rudest and most refractory materials to administer to the utilities and amenities of life. It will have been seen that some of the most unseemly are the most important, and that some of the most beautiful and expensive products are, in reality, the least valuable; fashion and caprice, or, it may be, vanity to obtain an exclusive possession, often attaching enormous prices to glittering fragments which it is impossible to turn to a single useful purpose. But waiving these unaccountable freaks, commercial utility has, in general, fixed upon the known minerals their proper relative values, and has stamped them all, whether worth one penny or worth one pound per ton, as Treasures of the Earth.