On CrystaUographj . 459 



character on which the last step would dcpciul, by which 

 to attain our object. Thus the tnste joined to the cvibical 

 form would instaiiilv indicate inunatc oFsoda. A metallic 

 colour of a bronze yellow reflected by a body oi' the sauic 

 form would characterize sulphurated iron. 



I". Struciure. Mechanical Division, The character 

 furnished by this operation is, as we have already re- 

 iTiarked, the onlv one which does not participate in the 

 variations produced by the mixture oF heterogeneous sub- 

 stances, the influence of" which modifies the hardness, 

 spe-ific gravitv, fusibility, &c. and even the results of the 

 analysis. It n»ay perhaps disappear in the unshapen masses 

 which have undergone a confused crystallization ; but 

 wherever it is possible nicrely to have a glimpse of it, it 

 is susceptible neither of more nor of less. It removes in 

 some measure every thing which is merely accessary in 

 the composition of a substance; and uhite in alt other 

 respects this substance marches through a succession of 

 shades, the measurement of the primitive angles stops at 

 the same degree ; and as soon 'as the substance changes its 

 nature, there is an abrupt leap in the value f)f the ancles. 



VVe may venture to hope, iftat those who peruse this 

 treatise with attention will perceive the advantage which 

 we have made of the character in question, for the deter- 

 mination of the species. In our lirst researches we had 

 nothing further in view- than to make it the basis of a 

 theory fitted for throwing lights on crystallography. But 

 the various applications which we have made of this theory 

 led us to exclude from such a species crystals uhich h.ad 

 been rei'erred to it, and which rejected the laws of structure 

 of which the forms relative to this species were suscepti- 

 ble; whereas other crystals, hitherto placed in diiVcrent 

 species, were subject to laws which solicited ihcir iiuin^acv; 

 and fron) that moment we conceived that this theorv, \vhii7h 

 at first appeared restricted to a simple branch of mineraloefv, 

 could extend its influence to the whf)le science, and con- 

 tribute to give more regularity and justness in the distri- 

 bution of the subjects which it embraces. 



IS. Fracture. This ouglu not to he confounded with 

 structure. Having broken a mineral, wlien we |)erceive 

 internally a scaly, granulous or fibrous texture, this is the 

 cflect of an arrangement which preexisted in- the body. 

 But if we find an undulated surface, or a species of small 

 .scales, which are nothing else than vcrv thin frai^ments, 

 ^\\\\ partly adhering to the substance, this aspect is the 

 effect of fracture. But as it depends origii>allv on a certain 



mode 



