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Ch. 5: Garnet

Ch. 5: Garnet Page of 296 Ch. 5: Garnet Text size:minus plus Restore normal size   Mail page  Print this page
174
PRECIOUS STONES.
The group of minerals designated by the name of garnets furnishes one of the most remarkable applications of the grand theory of isomorphism.
Under this name are comprehended minerals dif­fering much in colour, in specific gravity, in chemi­cal composition, &c.; but whose fundamental form never changes, and which even presents a very
small number of secondary modifications. Garnets are always crystallized, and they appertain to the tesseral system. Two secondary forms only are nearly always produced, the rhombic dodecahedron (Fig. 80), and the trapezohedron (Fig. 81).
In a scientific classification Rose, and the greater number of mineralogists with him, admit eight species of garnets, but two only furnish products for jewelry ; these are:—
Ch. 5: Garnet Page of 296 Ch. 5: Garnet
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