On Cnjstallographif. 103 



mcfi'ectual attempts in extracting its rhomboidal nucleus, 

 which excited my surprise, mixed with the hope that I 

 might succeed still further. 



Let us take as a second example — the metastatic crystal 

 (fig. 6,) the nucleus of which was found by Bergman. You 

 inay obtain this nucleus speedily by makina; a first sec- 

 tion upon the edges EO, OI; a second upon the edges 

 I K, GK ; a third upon G H, E H ; a fourth upon 01, IK; 

 a fifth upon G K, GH; lastly, a sixth upon E H, EOj 

 whence it follows, that the edsres of which we are speaking 

 are confounded with the lateral edges of the primitive form, 

 as we may judge from a simple inspection of fig. 7, which 

 represents this primitive form inscribed in the dodecahedron 

 with scalene triangles. 



There exist many other varieties of carbonated lime, se- 

 veral of which have very compound forms, and all of th^em 

 contain a nucleus precisely similar to that under considera- 

 tion. But if it be singular to see this nucleus issue from 

 varieties which are removed from it mostly by their configu- 

 ration, we have far less reason to expect it in those which 

 of themselves have a rhomboidal form with different mea- 

 surements of angles. We are at present acquainted with 

 live of these rhomboids*, one of which is much more ob- 

 tuse than the nucleus, and tlic four others have summits al- 

 ways more acute. This gradation, all the terms of which 

 are referred to one and the same species of solid, would seem 

 at first sight to give some colour to the opinion that primi- 

 tive forms are not constant relative to One and the same 

 mineral. But I have ascertained that all these rhomboids 

 concur in exhibiting, by sections made in dift'erent direc- 

 tions, a nucleus similar to that whose grand angle is 

 I0J°32'; and thus the paradox which arises from tJie diver- 

 sity of their angles is cleared up by the double employment 



•^ Bc;jinnin:5 witli that which is obtuse, we have tlic following v.-ilues for 

 tiie plane angle ol llie summit-: 



I I'lo IS' 5e" 



87 42 :50 



75 31 20 



45 S4 22 



37 31 4 

 Mineralo^^ists for a long period liave only been acquainteJ witli the firit 

 and third of tl'.e.-.e rhomhoicL. We sec from lJer;^i)ianV memoir, which 1 have 

 ■Ireidy quoted, that lie confounded tlic rhomhoid ill" 18' with the pri- 

 mitive, ill whiciithe anj^ic of the suminits is 101" ;J2'. On the other liarui, 

 Rome de I'klc considered that of 75" ;>l' as a second primitive form of cal- 

 careous spart;, hccau^e he saw no method ofreferrin;^ it, even by truucaturcs, 

 to that of lOl" 32'. Sec Berginan'i work on the character of tiiineralt. — 

 TuHeau l.iilu>logi({ue. 



G 4 of 



