6 TRANSACTION'S OF THE [OCT. 4, 



arrow-shaped crystals i^roduce the asteria or star effect, if the 

 gem is cut in en caboclion form with the center of the hexagonal 

 prism on the top of the cabochon. I have failed to find any of 

 them in the stones under consideration, or even any of the 

 marking of the hexagonal crystal which can often be seen when- 

 a gem is held in a good light, and the light allowed to strike 

 obliquely across the hexagonal prism. Dr. Isaac Lea has sug- 

 gested' that these acicular crystals are rutile, and interesting 

 facts and illustrations have been published by him. From my 

 own observations on many specimens, I believe there is little 

 doubt of the truth of this hypothesis.^ My explanation is, that 

 they were deposited from a solution, either heated or cold, while 

 the corundum was crystallizing, and I doubt very much whether 

 they will ever be found in any substance formed by fusion. 



The hardness of these stones I found to be about the same as 

 that of the true ruby, 8.8, or a little less than 9, the only differ- 

 ence being that the artificial stones were a trifle more brittle. 

 The testing point used was a Siamese green sapphire, and the 

 scratch made by it was a little broader but no deeper than on a 

 true ruby, as is usually the case with a brittle material. After 

 several trials I faintly scratched it with achrysoberyl, which will- 

 also slightly mark the true ruby. 



The specific gravity of these stones I found to be 3.93 and 

 3.95. The true ruby ranging from 3.98 to 4.01, it will be seen 

 that the difference is very slight, and due doubtless to the })res- 

 ence of the included bubbles in the artificial stones, which 

 would slightly decrease the density. As a test, this is too deli- 

 cate for jewelers' use ; for if a true ruby were not entirely clean 

 or a few of the bubbles that sometimes settle on gems in taking 

 specific gravities were allowed to remain undisturbed, it would 

 have about the same specific gravity as one of these artificial 

 stones. 



I found, on examination by the dichroscope, that the ordinary 

 image was cardinal red, and the extraordinary image a salmon 

 red, as in the true ruby of the same color. Under the polari- 

 scope, what I believe to be annular rings were observed. With 

 the spectroscope, the red ruby line, somewhat similar to that in 

 the true gem, is distinguishalile, although perhaps a little nearer 

 the dark end of the spectrum. 



The color of all the stones examined was good, but not one 

 was as brilliant as a very fine ruby. The cabochons were all 

 duller than fine, true stones, though better than poor ones. 

 They did not differ much in color, however, and were evidently 



1 Proc. Philad. Acad. Sc, Feb. 16, 1869, and May, 1876. 

 ^ Paper on star garnets, N. Y. Acad. Sc, May, 1886. 



