INTRODUCTION. 



THE immediate purpose of the science of Crystal- 

 lography, regarded as a branch of Mineralogy, is to 

 teach the methods of determining the species to 

 which a mineral belongs, from the characters of its 

 crystalline forms. But the science itself is also capa- 

 ble of being rendered more extensively useful. 



The crystalline forms of pharmaceutical prepara- 

 tions will furnish a certain test of the nature of the 

 crystallised body, although it will not determine its 

 absolute state of purity. In chemical analysis, the 

 forms of crystals will frequently supersede a more 

 rigorous examination of the crystallised matter; and 

 commercial transactions in the more precious mine- 

 ral productions may frequently be guided by the 

 crystalline form, or by the character of the cleavage 

 planes, of those bodies. 



It does not appear in the works hitherto published 

 that the connection between the crystal and the mine- 

 ral has been any where so systematically explained as 

 to enable the mineralogical student readily to connect 

 the one with the other. 



The Abbe Haiiy's works on crystallography are the 

 only ones in which a truly scientific exposition of the 

 theory of crystals is to be found ;* but by designating 



* An interesting volume on Crystallization, founded on the Abbe 

 Hauy's theory, was published in 1819, by Mr. Brochant de Villiers, 

 and will afford the reader a clear view of that theory, connected 

 with other interesting objects relating to the formation of crystals. 



