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tion of specimens of this stone, and of various other species which 

 were long thought analogous, but are. now found to constitute with 

 it a genus of some extent. This substance, we are now told, pre- 

 sents itself to our senses, especially to our sight, under two very dis- 

 similar appearances. The first is the original corundum imported 

 under that name and also under that of adamantine spar. At times 

 it is brought in irregular fragments, but often in crystals, which are 

 generally of a pretty large size. Those of the other appearance are, 

 in fact, the gems hitherto known by the names of Sapphire, Ruby, 

 &c. Another distinction is next made, according to the texture or 

 fineness of the grain of these stones ; the former being called imper- 

 fect, and the latter, or the gems, perfect Corundum. 



The author now enters into a minute account of the appearances 

 and the principal properties of this substance. And first he treats of 

 its colour. This, he tells us, is at best but an uncertain character in 

 stones, but yet it may at times afford some secondary marks of di- 

 stinction. The common or imperfect corundum varies, in this respect, 

 according to the country where it is found. That from the Carnatic 

 is of a grayish white, sometimes approaching to a pale green, and 

 sometimes, though rarely, of a red or blue colour : that from China 

 and Ava is generally of a dull green or brown colour ; and that from 

 the coast of Malabar appears of a reddish brown. 



The perfect corundum which is found in Pegu and in Ceylon is 

 either red, blue, or yellow. The former is the Oriental ruby ; the 

 blue is the sapphire ; and the yellow the topaz. From a duly pro- 

 portioned mixture of the blue and the red is produced the purple 

 colour, which constitutes the Oriental amethyst. The union of the 

 blue and yellow forms the green colour, which is proper to the Ori- 

 ental emerald ; and a larger proportion of yellow produces the colour 

 proper to the chrysolite. 



2. As to transparency, the crystals of corundum from the Carnatic, 

 having usually rough surfaces, are of course very imperfectly diapha- 

 nous ; but when broken, their fragments have generally a certain de- 

 gree of semi-transparency : most of these fragments, when held up to 

 the light, show a number of fissures in their substance, which in a 

 great measure prevent the transmission of light. These fissures arise 

 from a want of cohesion between all the parts of the crystalline la- 

 minae. The red and blue corundum of the Carnatic has a greater 

 degree of transparency than those of any other colour ; the blue in 

 particular having generally the preference in this respect. 



3. In hardness the corundum comes next to the diamond ; but this 

 quality, with regard to intensity, differs greatly, according to the co- 

 lour ant degrees of purity of the specimens. The corundum of the 

 Carnati \ when it is neither blue nor red, is less hard than any other 

 sort ; wnilst the imperfect blue species exceeds all the other varieties 

 of this kind in hardness, such is its density that it will emit pretty 

 bright sparks when struck with steel. 



4. This substance, like quartz, becomes phosphorescent by colli- 

 sion. The crystals of a red colour, whether of the perfect or im- 



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