Class G geocrystalline, in planetary classification, is a type of planet. The relatively young geocrystalline worlds have also been classified as class F planets on other scales, and are possessed of a mostly carbon dioxide atmosphere with some toxic gases, released as the planet cools and crystallizes. Lifeforms usually only exists as single-celled organisms due to the absence of free water on the young world. These planets are generally between three to four billion years old and measure 10,000 to 15,000 kilometers in diameter. (ST reference: Star Charts)