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Art. II. — Observations on the Relation between the Optical 
Structure and the Chemical Composition of the Apophyllite 
and other Minerals of the Zeolite Family^ in reference 
to the preceding Analyses of M. Berzelius. By David 
Brewster, LL. D. F. B. S. L., & Sec. R. S. Edin. 
The analyses described in the preceding paper, and obtained 
by the first analytical chemist of the present age, possess a high 
degree of interest, when considered merely in reference to mi- 
neralogy and analytical chemistry. The relation, however, 
which they bear to the optical or polarising structure of mineral 
bodies, is perhaps still more important, as they become esta- 
blished data, to which we may confidently appeal in establish- 
ing the universal infallibility of optical analysis, as affording es- 
sential and distinguishing characters of mineral bodies. 
In the preceding letter, M. Berzelius has proved, beyond a 
doubt, that in the present condition of chemical analysis., the 
Tesselite possesses the same ingredients as the Apophyllite of 
Uto ; and he is of opinion, that, as it is chemically the same sub- 
stance, it ought not to be regarded as a separate mineral species, 
and distinguished by a separate name. 
In the present case, therefore, the results of Chemical analysis 
are apparently set in opposition to those of Optical analysis, 
and it is incumbent upon those who confide in the latter to 
give some plausible explanation of this apparent discordance. 
There are at present only three scientific methods by which 
new mineral species can be discovered, 
1. The Method of Chemical Analysis, by which we discover 
the different elements of which minerals are composed, and the 
different proportions in which these elements are combined. 
2. The Method of Crystallographic Analysis, by which we 
ascertain the mechanical structure of crystals by cleavage, and 
thus obtain for each mineral species a primitive form, to which 
all its secondary forms may be referred. 
The Method of Optical Analysis which enables us to 
determine the primitive form of minerals from the number of 
• In M. Berzelius’s Nouveau Systeme de Mineralogie, published in Paris in 
1819, p. 307., he has stated, we presume by mistake, that the experiments on the 
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