Garnets can be used by geologists as a gauge of how much temperature and pressure the rock has endured. As a gemstone, garnets have had a mixed reputation. However, many people consider garnets to be inferior to other colored gems. Garnets are greatly variable in colors and varieties, though, and many of these are both rare and beautiful, producing genuinely precious gemstones. Some garnets are truly unique in the mineral kingdom and have much to offer as both gemstones and mineral specimens.
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.