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Crystallography. — "The system of crystallization of the dwmxmd" 

 by Mr. A. L. W. E. van der Veen, candidate mining engineer. 

 (Comin. by Mr. Molengraaff). 



(Communicated in the meeting of June 29, 1907). 



There still exists some doubt about the system of crystallization 

 of' the diamond. Although the tetrahedral hemihedrism of the diamond 

 is pretty generall)- accepted, still the opinion that it belongs to the 

 regular system, also finds support. 



The existing uncertainty is caused by the lack of' physical research 

 with regard to this question. Such a research into the existence or 

 non-existence of polarity of the trigonal axes has now been made- 

 With that object in view the trigonal axes of the diamond were 

 tested for pyro-electricity according to P. P. Koch's method 1 ). 

 Tourmaline, boracite and quartz, which evinced strongly pronounced 

 pyro-eleclrical characteristics, were used as testminerals. The result 

 arrived at is absolutely negative. The diamond is not pyro-eleetric, 

 and the trigonal axes do not possess polarity. 



Besides, researches were made into the crystalline form of the 

 diamond out of a collection of 367 uncut diamonds collected by 

 Mr. Molengraaff. Practically all types of crystallization were repre- 

 sented here, to explain which tetrahedral hemidedrism for the diamond 

 had been accepted in numerous writings of' Gkoth, Sadebeck, Martin 

 and others. The result of this investigation, which is not yet at an 

 end, is that a rational explanation of all irregular and apparently 

 tetrahedral-hemihedral crystalline forms of the diamond can be found 

 in the peculiar octahedral lamellar structure of the diamond. 



On this ground it may be accepted that the diamond crystallizes 

 in the holohedral division of the regular system. 



v ) P. P. Koch. Ueber eine neue Methode zur Untersuchung auf Pyroëlektricitat. 



Inaua. Dissert. Miinchen, Mainz 1902. 



