Conversations on Mineralogy. 157 
fail to derive a great deal of valuable information. We wish 
wodanium had been omitted. 
The fourth and fifth conversations contain the continuation 
of the external characters,—Crystallography ; the Goniometer, 
common and reflective, and their’uses; irregular external forms 
of Minerals; Transparency, and other characters, as fracture, 
cleavage, &c.; use of the Electrometer; Magnetism ; and the 
use of the Blow-pipe, Fluxes, &c. These also are instructive 
conversations. The derivation of a secondary crystal from the 
primitive form, is clearly and familiarly explained, by references 
to several figures of dissected crystals, which are executed 
with that accuracy and elegance that distinguish the works of 
Mr. and Miss Lowry. Indeed the whole of the figures, of 
which there are no fewer than 403, do them great credit. All, 
except the first 31, are outline engravings of crystalline forms. 
The sixth conversation begins the more immediate subject 
of mineralogy. Of her arrangement we shall let Miss Lowry 
speak for herself. 
Every system of mineralogy must be founded either on the chemical, 
or on the physical, characters of minerals, or on a combination of both, 
The latter are the most convenient (if not the most useful, ) and, therefore, 
are most generally adopted ; but there is a great diversity of opinion on 
au important question which naturally suggests itself, where to begin? 
The French mineralogists, who have paid great attention to the crystalli- 
zation * of minerals, considering it as their most important character, have 
in general placed at the beginning of their systems those minerals which 
are composed of an earth and an acid. The mineralogists of the German 
school appear to have selected a substance arbitrarily as the first in their 
arrangements, and to have formed their genera and families with much 
less regard to the chemical, than to the physical, characters; and even 
amongst these, have paid least attention to that which is certainly, where 
it exists, the most unvarying ; I mean crystalline form. But I think we 
should try to discover whether there is (be) not any kind of natural order, 
which might, at least, in some degree be observed in the formation of a 
SysteM......- 
We know that the great masses which constitute the crust of the globe 
are chiefly earths ; these are by far more abundant than the metallic, al- 
kaline, or inflammable substances, and are considered to be in general 
more ancient.--+-«+ 
I therefore begin with silica (in its purest form,) as it is the most ancient 
and most abundant of all mineral substances. Minerals are frequently 
divided into four classes, viz-, the earthy, the saline, the metallic, and the 
inflammable + minerals. 
Many celebrated mineralogists, however, subdivide the first class into 
earthy and acidiferous earthy minerals, which renders the arrangement 
rather more chemical, and which I have adopted.—p. 101—10s. 
To this we subjoin an outline of the tabular view of her 
arrangement. 
* “«Itis to the Abbé Haiiy that we are indebted for the explanatory 
theory of the structure of crystals.” 
+ “ Inflammable and combustible are not synonymous terms. All metals 
are combustible ; that is capable of uniting with oxygen ; but they will 
not burn in atmospheric air, and are, therefore, not called inflammable.” 
