The Brazil topaz is esteemed the most valuable next to the Oriental one: it is of a fine yellow, with an orange tint, and takes a very good polish. This topaz, weighing only one carat, is valued, if perfect, at six French livres (5s.), and encreases in value according to its weight, which is determined by the following calculation, as made for the Oriental topaz. Mr. Dutens esteems the Oriental topaz, when perfect, at sixteen French livres (13s. 4d.) the first carat. To know the value of one weighing three or four carats, it is requisite to multiply the one by the other, and to multiply the product by 16; the same rules to be observed for topazes of a greater weight; so that an Oriental and perfect topaz, valued at sixteen livres (13s. 4d.) the first carat, weighing sixteen grains, or four carats, would be worth two hundred and fifty-six French livres (10l. 13s. 4d.), whilst a Brazil topaz weighing likewise four carats, would be only worth ninety-six French livres[55] (4l.). There is also another sort of topaz in Brazil, of a very particular nature: it is of a very variable and extraordinary hue, and, being put into a small crucible, filled with ashes, on a slow fire, and taken off when the crucible becomes red, loses its yellow orange colour, and changes to that of the real Balas ruby, the tinge of which is generally beautiful. This topaz is frequently of a dark, smoky, dirty yellow, and was very little esteemed till a jeweller by chance discovered the abovementioned process, which was kept a profound secret, till Mr. Dumelle, goldsmith and working jeweller, disclosed it to the Academy of Sciences of Paris, by the means of Mr. Guettard.[56] Many people are of opinion, that the rubies at present brought from Brazil are merely topazes, which have undergone the said operation. The fine crystallization of the Oriental ruby is octoedrical equally with the diamond. That of Brazil crystallizes in prismes, of unequal planes, terminating in pyramids, there are likewise other rubies of a rounder form, owing to their having been rolled in the water. This stone is supposed to take its red colour from iron. The most esteemed rubies come from the island of Ceylon, and are thought more valuable than even those from Pegu. The _rubacelle_, or small ruby, very common in Brazil, is of a pale red, with a yellow cast; and is the cheapest and least esteemed of any stones of that description; they, however, take a very good polish; and the most perfect amongst them are sometimes passed off for _Balas_ rubies. This last stone may be estimated at thirty French livres (1l. 5s.) one carat; those of two carats at sixty French livres (2l. 10s.), those of three carats at ninety livres (3l. 15s.), and those of four carats at one hundred and twenty livres (5l.), &c.