triple Sulphuret, of Lead, Antimony, and Copper , &c. 49 
A . 6 . ; * the red garnet from the same place ; and the yellow 
garnet of Corsica fg-. 
Nevertheless, although the various molecules which, by means 
of this last-mentioned mode of attraction, unite themselves to 
mineral substances during their formation, do not cause any 
change in their chemical nature, they frequently, as I have 
already observed, occasion an alteration in their physical con- 
struction ; and very often induce variations in such of their 
characters as most immediately depend upon that construction, 
such as, their specific gravity, their hardness, their transparency, 
and even (particularly in the class of stones) their colour. It is 
therefore necessary that the mineralogist should fix his chief 
attention upon this mode of attraction, in order that he may be 
able to understand the accidental causes of the variations to 
which the substances under his examination are subject. The 
chemist also ought always to bear in mind the existence of such 
causes, as they may be fairly suspected, in most of the substances 
whose nature he attempts to investigate by his analysis. If he 
neglects to do this, he will be constantly liable to confound, in 
the result of his operations, those products which really belong 
to the chemical composition of the substances he examines, with 
those which are foreign to it. 
The foreign particles which the heterogeneous attraction of 
aggregation thus introduces into mineral bodies, necessarily 
affect their homogeneity. Yet, when that mode of attraction has 
taken place with all the perfection of which it is susceptible, the 
* The black garnet from Frascati near Vesuvius, of which Mr. Werner (for I 
know not what reason) has made a particular species, was also found by Mr. Klap- 
roth to contain of iron ; whereas Mr. Vauquelin found the proportion of iron 
in this kind of garnet to be as high as 
MDCCCIV. H 
