84 Count DE Bouhnon on the Laumomte. 



the new planes produced on the first, while the planes which occur 

 in the second, are more or less distant from it. 



The difference which exists between what has been said by the Abbe 

 Haliy in his " 'Tableau Comparatif^ Eifr." with regard to the form of 

 the primitive crystal of the laumonite, and that which I have myself 

 established respecting it, will no doubt excite surprise. This differ- 

 ence for a long time detained me. The estimation, in which this cele- 

 brated mineralogist is so justly held, made me redouble my attention 

 and care in the examination of this substance, but the several results 

 of my inquiries have always afforded me the fullest confirmation of 

 what I have said of the form of its primitive crystal, and of the 

 measure which I have given of its angles. The circumstances that 

 probably led the Abbe Haiiy into an error, are the different varieties 

 of crystals I have mentioned as forming the aggregations to which 

 the fasciculated masses of the laumonite belong, but which, when this 

 substance has undergone any alteration, are detached with much 

 facility, producing so many isolated crystals, a great number of which 

 present varieties differing one from the other. He would without 

 doubt have obtained in this way a crystal analogous to that repre- 

 sented in fig. 14, as I have myself done, and which in reality pre- 

 sents a rectangular octohedron with its faces unequally inclined, 

 and, regarding all the faces of this crystal as arising from a natural 

 cleavage, he may have adopted it as being the primitive form of 

 this substance. But two of the faces of this crystal are by no 

 means primitive ; they belong to the sixth modification. In no 

 instance could the angles of this crystal be such as the Abbe 

 Haiiy has given them : the four faces which belong to the lon- 

 gitudinal ones of the primitive rhomboidal tetrahedral prism, 

 meet each other two by two at an angle of 92" 30 ; and the 

 other four, of which two belong to the terminal faces of the primi- 



