Description
The garnet group contains minerals with a cubic crystal system and crystals in the shapes of rhombic dodecahedra and trapezohedra. They are nesosilicates with the general formula A3B2(SiO4)3. Garnets can contain the chemical elements calcium, magnesium, aluminum, iron2+, iron3+, chromium, manganese, and titanium. Garnets do not exhibit cleavage. The hardness is 6.5–7.5, and garnets can be transparent to opaque. The name "garnet" comes from the Latin word granatus, which refers to malum garanatum (pomegranate), a plant with red seeds that resemble many garnet crystals. Contrary to popular belief and the name's suggestion, garnets are not always red, but can be purple, red, orange, yellow, green, brown, black, or colorless. In 1998, a blue-pink garnet was discovered for the first time in Bekily, Madagascar. This variety is considered very rare. The six most common varieties are pyrope, almandine, spessartite, grossular, uvarovite, and andradite. These occur in two solid solution series: 1. The pyralspite group: pyrope-almandine-spessartite 2. The ugrandite group: uvarovite-grossular-andradite. Garnets are very common in the lower crust and mantle and thus play a major role in the chemical understanding of the Earth. Garnet is one of the "nine gems" in the Thai Order of the Nine Gems.
