Garnet belongs to the cubic system of crystalline symmetry. Its crystals are commonly of two kinds, both of which are very characteristic, the regular dodecahedron, _i.e._ twelve-faced figure (Fig. 75), and the tetrakis-octahedron or three-faced octahedron (Fig. 76); the latter crystals are, especially when weather- or water-worn, almost spherical in shape. Closer and more refined observations have shown that garnet is seldom homogeneous, being usually composed of several distinct individuals of a lower order of symmetry. Although singly refractive as far as can be determined with the refractometer or by deviation through a prism, yet when examined under the polarizing microscope, garnets display invariably a small amount of local double refraction. The transition from light to darkness is, however, not sharp as in normal cases, but is prolonged into a kind of twilight. In hardness, garnet is on the whole about the same as quartz, but varies slightly; hessonite and andradite are a little softer, pyrope, spessartite, and almandine are a little harder, while uvarovite is almost the same. All the varieties except uvarovite are fusible when heated before the blowpipe, and small fragments melt sufficiently on the surface in the ordinary bunsen flame to adhere to the platinum wire holding them. This test is very useful for separating rough red garnets, pyrope or almandine, from red spinels or zircons of very similar appearance. Far greater variation occurs in the other physical characters. The specific gravity may have any value between 3·55 and 4·20, and the refractive index ranges between 1·740 and 1·890. Both the specific gravity and the refractive index increase on the whole with the percentage amount of iron. Garnet is a prominent constituent of many kinds of rocks, but the material most suitable for gem purposes occurs chiefly in crystalline schists or metamorphic limestones. Pyrope and demantoid are furnished by peridotites and the serpentines resulting from them; almandine and spessartite come mostly from granites. The name of the species is derived from the Latin _granatus_, seed-like, and is suggested by the appearance of the spherical crystals when embedded in their pudding-like matrix.