Theory of CrjflaUifatlon. $JJ 



fblids terminated by fix faces parallel two and two; the 

 regular tetraedron ; the o&aedron with triangular faces ; the 

 hexagonal pril'm; the dodecaedron with rhomboidal planes; 

 ^and the dodecaedron with ifofceles triangular planes. 



Among thefe forms, there are fome found as nucleus, 

 which have the meafure of their angles different in different 

 kinds of minerals. This will appear lefs furprifing when 

 we confider that thefe nuclei are compofed in the firft in- 

 fiance of elementary moleculae, and that it is poffible the 

 fame form of nucleus may be produced in one kind by ele- 

 ments of a certain nature, and in another kind by different 

 elements ; as we fee integral moleculae, fome cubic and 

 others tetraedral, produce fimilar fecondary forms, in confe- 

 quence of different laws of decrement. But, it is worthy 

 of remark, that all the forms, hitherto met with as nuclei, 

 in the different fpecies, are among the number of thofe 

 which have a particular charafter of perfection and re- 

 gularity, as the cube, the regular oftaedron, the regular 

 tetraedron, and the dodecaedron with equal and fimilar rhom- 

 bufes for its planes. Thefe forms are a fort of limits at 

 which nature arrives by different routes, while each of the 

 forms, placed between thefe limits, feems to be attached tq 

 one unique kind, at lead as far as can be judged by the 

 prefent ftate of our knowledge on this fubjecl:, 



IV. Forms of the integral Molecuhs. 

 The primitive form is that obtained by feftions made on 

 all the fimilar parts of the fecondary cryftal ; and thefe fec- 

 tions, continued parallel to themfelves, conduct to a determL 

 nation of the form of the integral moleculae, of which the 

 whole cryftal is an afiembl3ge. This requires certain con- 

 federations that relate to the moft delicate point of the theory, 

 which I fhall now explain, with as much precifion as the 

 narrow limits to which I am obliged to confine myfelf will 

 allow. 



There 



