TERMINOLOGY. . 178. 



SECTION II. 



THE NATURAL-HISTORICAL PROPERTIES OF COM- 

 POUND MINERALS. 



. 178. REGULAR AND IRREGULAR COMPOSITION. 



The mode of composition in which the indivi- 

 duals of the mineral kingdom appear, is said to be 

 regular , if the form produced by their connexion 

 is a regular one, and if this regularity is a neces- 

 sary consequence of the composition ; if the con- 

 trary takes place, the composition is said to be 

 irregular. 



If two or more homogeneous individuals join in a com- 

 pound form, regularly and symmetrically, at least if duly 

 completed ; the composition is in every respect perfectly 

 determined. For we may indicate, with the greatest accu- 

 racy, in which faces of the simple forms, or in which plane 

 the individuals cohere, even though this plane should not 

 be parallel to a face of any simple form of that species 

 to which the individuals belong. In general we may ob- 

 tain the situation of the individuals required, or necessary 

 in order to produce the compound form. A composition 

 of this kind is said to be regular. 



The composition is irregular, if the forms are not con- 

 nected in the manner now described, and if, therefore, 

 they do not produce any regular or symmetrical forms. 

 Two or more individuals joined in this way, are said to be 

 merely aggregated, an expression which intimates, that there 

 is no regularity in their composition. 



There are compound minerals, which affect regular ex- 

 ternal forms, although their composition is in fact irre- 

 gular. The regularity of the form in such cases evidently 

 does not follow from the composition, but it must originate 



