Diamonds and precious stones, a popular account of gems .. . re cut and placed in the same manner, itis possible to construct several edifices resemblingeach other in form and disposition. That which Art accomplishes more or less com-pletely, Nature realizes perfectly. Out of substances essentially differing in theirnature she constructs well-defined and crystallizedcompounds, which appear to all intents and pur-poses identical, and yet are not so. This phenomenon is called in science isomorphism,from the Greek isos, equal; and morphea form. Itwas discovered by the celebrated German chemistMit
Diamonds and precious stones, a popular account of gems .. . re cut and placed in the same manner, itis possible to construct several edifices resemblingeach other in form and disposition. That which Art accomplishes more or less com-pletely, Nature realizes perfectly. Out of substances essentially differing in theirnature she constructs well-defined and crystallizedcompounds, which appear to all intents and pur-poses identical, and yet are not so. This phenomenon is called in science isomorphism,from the Greek isos, equal; and morphea form. Itwas discovered by the celebrated German chemistMitscherlich, and the discovery is considered one ofthe greatest scientific achievements of our century. 174 PRECIOUS STONES. The group of minerals designated by the nameof garnets furnishes one of the most remarkableapplications of the grand theory of isomorphism. Under this name are comprehended minerals dif-fering much in colour, in specific gravity, in chemi-cal composition, &c. ; but whose fundamental formnever changes, and which even presents a very. Fig. 80.—Garnet, Rhomboidal type. Fig. 81.—Garnet, Trapezohedral type. small number of secondary modifications. Garnetsare always crystallized, and they appertain to thetesseral system. Two secondary forms only arenearly always produced, the rhombic dodecahedron(Fig. 80), and the trapezohedron (Fig. 8i). In a scientific classification Rose, and the greaternumber of mineralogists with him, admit eightspecies of garnets, but two only furnish products forjewelry ; these are:— GARNETS. 175 The Almandine. Grossularia.—This species is a double silicate oflime and alumina. As its constituents are col-ourless, either alone or combined, we should meetwith limpid garnets devoid of any tint. Such gar-nets, in fact, are found in certain localities of Nor-way, Mexico, and the Ural Mountains. But asiron—which Haiiy has called the great colouristof nature—is so extremely abundant, it becomesintroduced in proportions
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