Garnets are isostructural , meaning that they share the same crystal structure. This leads to similar crystal shapes and properties. The A represents divalent metals such as calcium, iron, magnesium and manganese. The B represents a trivalent metal such as aluminum, chromium, iron, and other elements found in rarer members of the group. The main differences in physical properties among the members of the garnet group are slight variations in density and index of refraction.
Garnets belong to the isometric crystal class, which produces very symmetrical, cube-based crystals.
This basic shape is the trademark of garnets, for no other crystal shape is so closely associated with a single mineral group like the rhombic dodecahedron is with garnets. Most garnets are red in color, leading to the erroneous belief that all garnets are red. In fact a few varieties, such as grossular, can have a wide range of colors, and uvarovite is always a bright green. As a mineral specimen, garnets usually have well shaped and complex crystals and their color and luster can make for a very beautiful addition to a collection. At times, garnets are accessory minerals to other valuable and pretty gem minerals such as topaz , beryl and tourmaline , making these specimens extra special.