INTRODUCTORY OBSERVATIONS. 7 



In these bodies the power of crystallization appears to have been 

 interrupted during their formation, and they have accordingly been 

 left in an incomplete state. Examples of this kind may be seen in 

 uncrystallized Quartz, massive Garnet, and common Feldspar. Such 

 minerals are in a similar condition with the defective or monstrous 

 individuals occurring in the organic kingdom. It will not appear 

 strange, moreover, that they should on the whole be much more 

 numerous among inanimate bodies than among living beings ; since 

 the individualizing power in the former, beside being confined to a 

 single cause, viz. that of crystallization, (. 11.) is liable to be af- 

 fected by a much greater variety of accidents than the latter. 



. 13. DECOMPOSED MINERALS. 



Decomposed minerals are those which have lost some of 

 those properties derived from the power of crystallization. 



Decomposed minerals are, either, only impaired in the color, lus- 

 ter, and hardness of their crystals, while the form is preserved, 

 as is the case with Laumonite, or they are reduced to the form of 

 powder and shapeless masses, wholly destitute of regular structure, 

 lustre, or constant degrees of hardness, and specific gravity, as in 

 the instance of Porcelain clay, derived from the decomposition of 

 Feldspar. Such bodies, obviously, are no more proper objects of 

 mineralogical determination than are the decayed portions of a plant 

 of botanical consideration. Still, it will generally be possible to dis- 

 cover what a decomposed mineral has been in its natural state, 

 though to effect this we must employ a different method from that 

 adopted in determining other minerals. 



Decomposed minerals are of rare occurrence, except at the im- 

 mediate surface of the earth, where minerals are exposed to a va- 

 riety of mechanical forces in addition to the chemical agency of 

 heat, air, and moisture. Still the progress actually made by these 

 disintegrating and decomposing agents is very limited. Many min- 

 erals continue to preserve the integrity of their characters, though 

 almost impalpably reduced in size ; and immense surfaces of rock 

 remain apparently unaltered from age to age amidst this incessant 

 warfare. 



