The blue variety of the corundum is the Oriental Sapphire of the jeweller. There is one hue of it of a soft pure azure, distinguished from the commoner kinds by its retaining its fine blue even by candlelight, when an ordinary sapphire looks purple or black. Unlike the ruby, it occurs in specimens of a considerable size. A good blue stone of ten carats is valued at fifty guineas. If it weighs twenty carats its value is two hundred guineas, but under ten carats the price may be estimated by multiplying the square of its weight in carats into half a guinea; thus one of four carats would be worth eight guineas. A sapphire of a barbel-blue colour, weighing six carats, was disposed of in Paris by public sale for 70l.; and another of an indigo blue, weighing 6 carats and 3 grains, brought 60l., both of which sums much exceed what the preceding rule assigns, from which we may perceive how far fancy may go in such matters.
The Spinels, whose transparent and more precious forms consist essentially of alumina combined with magnesia, and tinted perhaps with iron, include two resplendent stones, the Spinel Ruby, a scarlet variety of considerable fire and of rich colour, and the Balais or Balass Ruby, thus called from one of the most celebrated localities of the spinel in former times, namely Beloochistan or Balastan. The latter is of a delicate and rarely deep rose-colour, showing a blue tint when looked through, and a redder one when it is looked at. Both of these minerals are termed rubies by the jewellers, and the deeper-tinted kinds are sometimes sold for the true stone. In fact, nearly all the large and famous gems that pass under the name of rubies belong to this species, as for instance the ancient ruby in the crown of England, which was presented to Edward the Black Prince by Don Pedro the Cruel, and the enormous stone, time-honoured in Indian tradition, that came along with the Koh-i-Noor into Her Majesty’s possession. Such was the superstitious value attached to it by its former proprietor, Runjeet Singh, that he would sooner have lost a province than this stone. When the weight of a good spinel exceeds four carats, it is said to be valued at half the price of a diamond of the same weight.
The Chrysoberyl, called also by the jewellers the Oriental Chrysolite, is a stone of almost adamantine lustre and transparence. It is a compound of alumina and the rare oxide glucina, a constituent of the beryl. It has usually a peculiar, sometimes a very delicate greenish yellow or primrose colour, and is then one of the most beautiful of gems. The finer specimens are from Brazil.
The Emerald and the Beryl are one and the same mineral—a silicate of alumina and glucina, which owes to a small trace of iron its blue, pink, or yellow tints, or else to a little chromium the transcendent green which characterises it as the emerald. The colour of this beautiful gem is so pleasant to the eye that the ancients attributed to it the power of strengthening and relieving the sight when fatigued by previous exertions. Both from its beauty and rareness they held it in high estimation, and Pliny ranks the emerald in value immediately after the diamond and the oriental pearl. In the Egyptian tombs real emeralds are sometimes found as the ornaments of regal mummies, and they have not seldom been discovered among the ruins of Rome, or at Herculaneum and Pompeii. Scythia, Bactria, and Egypt were renowned among the ancients as the countries which furnished the most beautiful emeralds. At present these precious stones are obtained chiefly from New Granada and Siberia, in which latter country they occur of much larger size, but of less beauty, and consequently far inferior value. The first Siberian emeralds were discovered in the year 1831, in the neighbourhood of Catharinenburg, by some peasants, while making tar, and other mines were opened in 1834 ten versts distant from the former. Here was found an enormous stone, fourteen inches long and twelve broad, and weighing 16¾ lbs. troy, and another superb specimen consisting of twenty crystals, from half an inch to five inches long, and as much as two inches thick, embedded in a matrix of mica-schist. Both these monstrous gems now rank among the chief ornaments of the Imperial Mineralogical Cabinet.
When the Spaniards conquered Peru, they found many beautiful emeralds in the possession of the natives. The largest of these stones, about the size of an ostrich egg, was adored as a god in one of the temples, and other emeralds of a smaller size placed around it were honoured as its children. In their blind fanaticism, the otherwise greedy Spaniards shivered the god and his family to pieces, but it is more than probable that the wisest of the band quietly picked up the fragments and afterwards disposed of them to advantage. The finest stones used to be found in the valley of Manta; but the Indians kept the mines secret, to avoid being obliged to work in them, or perhaps out of hatred against their oppressors. At present, the American emeralds are chiefly obtained from the valley of Tunka, in the province of Santa Fé de Bogota, in New Granada.
The price of emeralds varies considerably, according to their purity, the beauty of their colour, their lustre, and their size. Before the discovery of America, they were uncommonly dear, all knowledge of the old mines having been lost, so that the emeralds still used as ornaments were all ancient. Afterwards their value decreased, when a greater quantity was imported from Peru; but recently they have again risen in price, as America at present furnishes but few good stones. A splendid specimen in the possession of Mr. Hope, weighing six ounces, cost 500l.; another fine American emerald belonging to the Duke of Devonshire is two inches long, and weighs above eight ounces, but, owing to flaws, it is but partially fit for jewellery.
The Beryl, which exhibits every gradation of tint, from a pale azure blue to a fine mountain green, and also occurs in a pale orange yellow variety, is found in great perfection at Oduntschilon and Mursinsk in Siberia. A beautifully clear crystal, ten inches long, discovered in the latter locality in 1828, and forming part of the mineralogical museum at Petersburg, is valued at 8,000l. Formerly Brazil and Cangayum in the Deccan were in much repute as fields in which the beryl was found, and many a brilliant little stone has been furnished by the Mourne Mountains in Ireland.
The Zircon consists of the mixed oxides of silicon and of the rare element zirconium, and is one of the heaviest and most lustrous of gem-stones. Its colourless variety is the nearest match in brilliancy and refractive energy for the diamond, while the deep orange-tinted red zircon is that transcendent gem, the true hyacinth, which makes a very superb ring-stone.
The Topaz, a silicate of alumina and fluorine, is found chiefly in Siberia, Brazil, and Saxony, and is also met with in the granitic detritus of Cairngorm in Aberdeenshire. The colourless Brazilian variety (Pingo d’agoa, or waterdrop) surpasses rock-crystal in purity and refractive power, and being of the same weight as the diamond, is sometimes mistaken for it. The pale yellow topaz when heated in a crucible assumes a rose-red colour, and is then called by the jewellers ruby of Brazil. The Saxon topaz, on the other hand, becomes white when exposed to heat, and thus deprived of colour is sold for the diamond. In ancient times the topaz was highly esteemed; but, in spite of its beauty, it is not now considered of very great value, from its being too frequently found, and is sold in the rough for about forty shillings per pound.
When of a beautiful ‘forget-me-not’ blue, and above the size of a pea, the Oriental Turquoise, which in inferior specimens is but of little value, fetches a considerable price, so that fine stones of about half an inch in length are worth 15l. or 20l. The turquoise, which consists of phosphate of alumina coloured by oxide of copper, occurs chiefly in the mountainous range of Persia, whence it is brought by the merchants of Bochara to Moskau; but the Shah is said to retain for his own use all the larger and finely tinted specimens.