^34 Mohs' System of Crystallography 
one with which the older mineralogists were acquainted. Cer- 
tain names, which have descended to us from those times, indi- 
cate this fact. The name pyrites has been applied to several 
minerals which do in reality belong to one order. This being 
the expression of unwarped and unprejudiced judgments, may 
be regarded as the first sketch of a natural system. 
53. Classes. — As the genera may be collected into orders, 
the orders in like manner may be collected into classes. Three 
such classes are to be found in the mineral kingdom. At pre- 
sent, it will suffice to mention what is included under them, as 
by this means their differences, and the facility with which they 
may be characterised, will best appear. The first class com- 
prehends the salts and the atmospherilia, as they are called ; 
the second comprehends the earthy and metallic minerals of 
Werner's system, with sulphur and graphite ; the third com- 
prehends combustible minerals, excepting sulphur and gra- 
phite. 
54}. Why Atmospherilia are introduced into the Mineral 
Kingdom. — Idea of a Mineral. — The only thing here deserv- 
ing notice is the introduction of atmospheric substances into the 
mineral kingdom. This results from the very idea of a mineral. 
According to Werner's explanation, this term includes under it 
the idea of geognostic indications, which are specified for the 
express purpose of excluding atmospheric substances. But the 
idea of a mineral in natural history ought to be purely natural 
historical^ and must not, therefore, have a reference to indications 
of a foreign kind. If such indications are omitted from Wer- 
ner's system, the only remaining principle is, that minerals are 
inorganic productions of nature^ as atmospheric substances 
likewise are. 
55. Idea of Mineralogy and Natural History. — In order 
finally to combine all the preceding results under one point of 
view, the scope of mineralogy itself must be taken into con- 
sideration. If mineralogy, as almost every writer acknowledg- 
es, at least in the first page of his work, is a department of 
natural history, and consequently the natural history of the 
mineral kingdom ; then it must serve the same purpose for this 
kingdom, as zoology serves for the animal, and botany for the 
vegetable kii^dom. Of all the departments into which natu- 
