60 
Mohs’ (rf Crystallography 
sistorkal iii(|uiiy concerning the varieties united into one spe- 
cies. The plan of a fundamental inquiry is still scarcely begun 
to be traced ; yet much has already been erected on it. Indeed 
forms out of all the four series of crystallizations are to be found 
united under one species, — in several, even in the latest Ger- 
man manuals. No attention has yet been bestowed to obtain an 
exact settlement of the hardness and specific gravity. But it is 
self-evident, and confirmed by many examples, that such negli- 
gent proceedings as these must needs be followed by indistinct- 
ness among the species ; and that, from the same cause, those 
species must also be split asunder, is shewn by many of the 
newest arrangements of our most celebrated mineralogists. 
13, Violation a universal rule in classification.-— \\, is a 
rule in every classification, that no one object shall appear in it 
more than once. Now all mineralogists agree in admitting, that 
porcelain earth is weathered prismatic felspar. But felspar, 
though weathered, is still felspar. Porcelain-earth cannot, 
therefore, be admitted into the mineralogical system as a sepa- 
rate species. The same is also the case with several others ; 
silver-black, copper-black, &c. 
14. Violation of a rule in natural history classification. — It is 
a rule in natural history classification, that its objects must be 
individuals alone, and these only in their state of greatest en- 
tireness, of complete formation. Hence it is, that mountain 
rocks not being individuals in this sense of the word, are ex- 
cluded from the system. Iron-Hint, heliotrope, jasper, tile-ore, 
clay, tripoli, yellow earth, and many others, are mixtures as 
truly as granite, though the component particles are undistin- 
guishable, by reason of their smallness. They are partly even 
mixtures of decomposed minerals. Hence no one of them can 
be introduced as a particular species into the mineral kingdom. 
Basalt, claystone, serpentine, &c. are likewise mixtures. Gases 
may happen, where a mineral can neither be said to be decom- 
posed nor mixed, though it occurs in a state which is usually 
the consequence of decomposition. This may take place with 
regard to some porcelain-earths, (those of Aue), to pure clay- 
earth, and some others. In respect of natural history arrange- 
ment, such minerals are to be described as incompletely formed, 
and regarded as decomposed. 
