ISO Topaz.' 



14. Topaz? 



[Communicated by the Rev Edward Hitchcock. J 

 «' This occurs in that rich repository of minerals, the Go- 

 shen granite, three miles northwest of the meeting-house, 

 associated with green tourmaline, cleavelandite, spodumene, 

 indicolite, rose mica, and pyrophysalithe. J found a portion 

 of a crystal of this mineral, nearly an inch in diameter; in 

 some specimens of this granite, which I collected for the 

 other minerals they contained. It is perfectly limpid, 

 although when lying in its bed, it has a delicate green tinge, 

 which is occasioned by the greenish crystals of mica that 

 surround it. The fracture in one direction is straight, and 

 exhibits a lamellar structure ; in all others, it is conchoidal, 

 and the lustre is vitreous. It exactly resembles the limpid 

 topaz from Rio Janeiro. It scratches quartz, but is itself 

 scratched by the spinelle." 



Remarks, 



Mr. Hitchcock having given me a specimen of the mineral 

 described above, and requested me to examine it, I have 

 paid such attention to it as has been in my power. Its spe- 

 cific gravity is about 3. — I cannot vouch for the accuracy 

 of the trial, because the weight of the portion which I ex- 

 amined was only 9 gr. and a larger piece might have given 

 it as high as it is usually stated, for the topaz — that is from 

 3.46 to 3.60.* Mr. Hitchcock's specimen scratches not 

 only quartz, but beryl ; it is perfectly transparent and 

 limpid, and so entirely foliated in its structure in one direc- 

 tion, that a little jar causes it to split into thin parallel 

 pieces, with brilliant and beautiful surfaces, while the cross 

 fractures are in every direction conchoidal. On comparing 

 it with a specimen of limpid topaz from Siberia, in Col. 

 Gibbs's cabinet I could discover no difference, except that it 

 was less brilliant. A very minute fragment when heated, and 

 presented to the fibres of cotton caused a slieht movement j 

 but T could not be positive that it was an electrical effect. 

 When exposed to the flame of the compound blow-pipe, it 

 readily melted with strong ebullition, and produced a glisten- 

 ing white enamel. It will be remetpbered that this was pre- 

 cisely the effect which I produced by the compound blow- 

 pipe upon the Saxon topaz in 1812, several years before Dr. 

 Clarke's experiments were made. — Editor. 



* I fonnd the specific gravity of a perfectly limpid white topaz from Sibe- 

 ria, the weight of which was 431 grains, to be 3.59— from Col. Gibbs's cabi- 

 net, the same mentioned above. 



