358 THE DIAMOND AND OTHER PRECIOUS STONES. 



idea that these meteorites are formed suddenly by the condensation of 

 exhalations from the earth. The regular disposition of the particles of 

 a substance in the form of a crystal requires immense time as ^Yell as per- 

 fect freedom of motion. 



From the peridot we pass to the garnet^ which is a ferruginous stone 

 of a deep-red color, and often Avantiug in transparence. It is, however, 

 sometimes found of the beautiful color called peach-bloom. To the per- 

 fection of colors it is necessary that a specimen should join a regularity 

 of tint, wanting which constitutes a defect easily perceived by an eye 

 Ijroperly trained. There is sometimes found with cut garnets a very 

 pretty assemblage of stones in juxtaposition, which gives a very agree- 

 able appearance of black mingled witli red. The only garnet I have ever 

 seen of any value is the hyacinthe, a stone of a luscious orangy yellow 

 color, having a little the appearance of candy made of brown sugar. 

 This stone, which Haliy wrongly separates from garnets, is not much 

 esteemed except by amateurs or collectors of curious specimens. The 

 Hollanders formerly- cut garnets into a pearl shai)e, Avhich were strung 

 in necklaces and used as money among the slave-traders. As in sap- 

 phires, asters may be observed in garnets, and I have been able to 

 verify, by the cutting, all that this phenomenon indicated of the struct- 

 ure of the stone. 



In the garnet can be developed crosses with six and also with four 

 limbs, besides straight and oblique crosses, without counting certain 

 circles of light resulting from a cutting perpendicular to the a si e rial ilia- 

 ments. 



Both for mineralogy and also for optics the study of gems affords 

 many important facts. It is to the study of mincralogical optics that 

 Mains, Arago, Fresnel, and Biot, in France ; Huygheus, in llolland ; 

 Wollaston and Sir David Brewster, in England; and Seebeck and 

 Haidenger, in Germany, owe so much of their renown, aj)d to which the 

 science of light is indebted for its most beautiful discoveries. 



Pliny gives no Latin name to the garnet, but confounded it with all 

 stones of a red color, under the head carlunculi. It is the heaviest of 

 gems, and like the diamond does not possess double refraction. From 

 the vrhite garnet of Norway very excellent microscopic lenses have been 

 made, although it is ordinarily from the diamond that small and exceed- 

 ingly powerful lenses of this kind are formed. The cutting of such lenses 

 is very difhcult, and the price commensurate with the labor and skill re- 

 quired in the operation. I may here observe that another mineralogi- 

 cal crystal having single refraction, the ampliigene^ strongly refractive 

 and i)erfectly colorless, may also perhaps be used to form small, powerful 

 lenses. 



The topaz, whose name is derived from its yellow color, is a mineral 

 which also crystallizes in prisms, and is susceptible of being very nearly 

 broken transversely. They are of all colors, and coine principally from 

 Brazil and Saxony, though Siberia also furnishes them. The price of 



