Introduction to the Study of Mineralogy . 395 



geometry, subjected to particular rules, and by which each 

 j^olid has its figure determined by the combination of an in- 

 finity of other small solids, which are like the elements of 

 the first. A hasty glance at crystals will obtain for them 

 the appellation of pure lusus natures ; which is only an ele- 

 gant way of confessing our ignorance. A closer examina- 

 tion unfolds to us the laws of arrangement in them, by the 

 aid of which calculation represents and unites to each other 

 the results observed ; laws so variable, and at the same time 

 so precise and regular; simple in the extreme, yet display- 

 ing the utmost fertility. 



The theory which has served to develop these laws, rests 

 entirely upon a fact the existence of which had been hi- 

 therto rather presumed than demonstrated. It consists in 

 this, that these small solids, which are the elements of cry- 

 stals, and which I call their integrant molecules, have, in all 

 those which belong to one and the same species of mineral, 

 one invariable form, the faces of which are in the direction 

 of the natural joinings indicated by the mechanical division 

 of these crystals, and of which the respective angles and di- 

 mensions are given bv calculation combined with observa- 

 tion. Besides, the integrant molecules relative to different 

 species also have diversities among them more or less re- 

 markable, except in a very few cases where their forms 

 have characters of regularity, whence result, as it were, 

 points of contact between certain species. It follows from 

 this, that the determination of the integrant molecules 

 should have a great influence over that of the species ; and 

 this consideration has led me more than onee, either to sub- 

 divide into several species a groupe which, in the ancient 

 methods, form only one, or to refer and re-unite the scattered 

 members of a single species, of which several distinct spe- 

 cies had been made. Some of these separations and re- 

 unions, made at a time when analysis had not yet unveiled 

 the true nature of the substances which were the object of 

 it, are now confirmed by chemical results ; and I shall even 

 venture to say, that upon the hypothesis that no mineral 

 Substance had been as yet decomposed, wc might, by a con- 

 tinued investigation of the integrant molecules, form assort- 

 ments. 



