These variations of color are more or less connected with differences of composition which it may be well first of all to consider. Garnet as a mineral is, like most minerals used as precious stones, a silicate. United with the silica the element most commonly occurring is aluminum. If calcium be united with these two the variety of garnet known as grossularite, or essonite, or cinnamon stone, is produced. If magnesium takes the place of calcium, then pyrope is formed. If iron, we have almandite, and if manganese, spessartite. Another variety of garnet, andradite, is composed of calcium and iron in combination with silica, and still another, uvarovite, of calcium, chromium and silica. Though they seem to differ so much in composition, all kinds of garnet crystallize in the same system and are closely allied in all their properties, so that it is always an easy matter to distinguish garnet of any variety from other minerals. Garnet crystals may be of the twelve-sided form, known as dodecahedrons, the faces of which have the shape of rhombs, or the twenty-four-sided form known as trapezohedrons, the faces of which have the shape of trapeziums. Quite as commonly occur crystals which are combinations of these two forms, and then exhibit thirty-six faces, as in the crystal from Alaska shown in the accompanying illustration. Sometimes the crystals attain considerable size, some perfect ones from Colorado weighing fifteen pounds, while crystals two feet in diameter are reported from North Carolina. A curious feature of garnet crystals is that of often inclosing other minerals. The garnets from New Mexico, for instance, when broken open are sometimes found to contain a small grain of quartz. In the crystals from East Woodstock, Maine, only the outside shell is garnet and the interior is calcite. Other crystals are made up of layers of garnet and some other mineral.