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Ch. 4: Classification of Minerals

Ch. 3: Minerals: Chemical Properties Page of 515 Ch. 4: Classification of Minerals Text size:minus plus Restore normal size   Mail page  Print this page
CLASSIFICATION OF MINERALS.                         129
Titanium in anatase, rutile, brookite, and titanite, is shown by the assay forming, with salt of phosphorus, in the oxidating flame, a glass which is and remains colorless ; in the reducing flame, a glass which appears yellow when hot, and whilst cooling passes through red into a beautiful violet. When iron is present, however, the glass is blood-red, but is changed to violet by adding tin. When titanate of iron is dissolved in hydrochloric acid, and the .solution boiled with a little tin, it acquires a violet color from the oxide of titanium. Heated with concentrated sulphuric acid, the titanate of iron produces a blue color.
CHAPTER IV.
CLASSIFICATION OF MINERALS.
A mineral species was formerly defined as a natural in­organic body, possessing a definite chemical composition and peculiar external form. The account given of these properties shows that the form of a mineral species compre­hends not only the primary or fundamental figure, but all those that may be derived from it by the laws of crys­tallography. Irregularities of form arising from accidental causes, or that absence 'of form which results from the limited space in which the mineral has been produced, do not destroy the identity of the speeies. Even amorphous masses, when the chemical composition remains unaltered, are properly classed under the same species, as the perfect crystal.
The definite chemical composition of mineral species must be taken with equal latitude. Pure substances, such as they are described in works on chemistry, are very rare
Ch. 3: Minerals: Chemical Properties Page of 515 Ch. 4: Classification of Minerals
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