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XIV. Preliminary Notice on Thirteen Systems of Crystallization 

 in the Mineral Kingdom, and their Optical Characters. By 

 Professor Breithaupt, of Freiberg, Councillor of Mines*. 



I^HE important discovery made by Councillor Jenzsch, that 

 tourmaline had two optical axes (PoggendorfFs Annalen, 

 vol. cviii. p. 645), certainly delighted no one more than myself. 

 Soon after reading that account it occurred to me that the same 

 character must be found in those crystals of apatite and idocrase 

 in which I had more than ten years since observed the asymme- 

 trical condition of the pyramidal planes with respect to the base. 

 Reich found the two optical axes beautifully distinct in a 

 fine crystal of apatite from Ehrenfriedersdorf, Pollachites 

 haplotypicus (see my ' Mineralogy, vol. ii. p. 277), having at 

 one pole a smooth basal plane, and at the other a good cleavage 

 plane. I estimate the angle that the two axes make at 6 degrees 

 at the least. 



The same applies,[though in a less degree, to|the apatite from 

 Schwarzenstein in the Zillerthal in Tyrol, which, however, T have 

 not measured ; perhaps in this case the axes are only 2 degrees 

 apart. 



The apatite from St. Gothard, Pollachites galacticus, which 

 I had measured, was polished, and I then found that it presented 

 the same characters as the one from Schwarzenstein. 



M. Lingke, the optician to the University, was kind enough 

 to cut and polish for me two plates of the green idocrase from 

 Piedmont (Idocrasius calaminus, B. M. p. 652) ; and I found two 

 axes in this also very plainly evinced. 



When I had obtained these results, I received a letter from 

 M. Jenzsch, saying that he also had found two optical axes in 

 apatite and idocrase. 



Col. von Kokscharoff has tried to set aside my measurements 

 of the idocrase. He believes that I used imperfect crystals for 

 these trials ; but he is wrong ; my measurements were not only 

 most carefully made but repeated very often, and I selected 

 the best crystals, viz. those from Piedmont, and I found the 

 inclination to the base as follows : — 



One plane = 152 55 



Two neighbouring planes . . . = 142 50 

 And the fourth, opposite the first . = 142 47 



Col. von Kokscharoff says he found the angle only =142° 46f 

 in all four planes. 



* Translated from the Berg- und Hiittenmannische Zeitung, by William 

 Hustler, Esq., and communicated by Professor W. H. Miller, F.R.S. &c. 



