5216 Professor Mohs's General Reflections on 
Decomposed minerals, such as porcelain-earth, and others, have 
been considered as distinct species, or they have erroneously been 
considered as varieties of other species to which they have some 
resemblance in their decomposed state ; as, for example, the de- 
composed hexahedral and prismatic iron-pyrites, which were 
comprised in the species of prismatic iron-ore. And were we 
finally to dispose the method itself, so as to make it applicable 
also to the decomposed natural productions, the method and the 
science itself would be annihilated, from the inconsistency which 
w r ould be introduced between its various departments. In con- 
formity with the preceding observations, the province of Minera- 
logy must be cleared, and its object determined, which consists 
in the natural-historical properties, while the natural bodies 
themselves are considered merely as the bearers of these proper- 
ties. 
Besides the natural-historical properties, minerals also assume 
certain others at the period of their formation, and retain them 
as long as they themselves continue to exist. Of this kind is 
the property of manifesting certain phenomena when brought 
under certain circumstances,, as, for instance, the property of 
changing colour, of intumescing, of melting, when exposed to 
the action of heat, of being soluble in acids, with or without ef- 
fervescence : the chemical composition itself is also of this nature. 
It is necessary to obtain a criterion for the strict distinction of 
these from the natural-historical properties. This criterion is 
found in the circumstance, that the latter do not contain any 
properties but such as manifest no change either in the proper- 
ties themselves, or in the substances which possess them, during 
their observation or examination, but retain their natural state 
undestroyed ; while those are excluded from the natural-histori- 
cal ones, which cannot be observed, unless a change be produ- 
ced in the properties or in the bodies to which they belong. 
Whenever any one of the departments of Natural History em- 
ploys these properties in its method, it transgresses its legiti- 
mate boundaries, is mixed up with other sciences, and is at last 
involved in all those difficulties, of which Mineralogy has long 
stood a warning example. 
But Natural History requires, that, even among those proper- 
ties which have been defined above, as natural-historical proper- 
ties, a selection must be made in reference to the mineral king- 
