Petrified wood, also referred to by the English term petrified wood, is a kind of fossil: it consists of fossil wood, in which all organic materials have been replaced by minerals (mostly silicates, such as quartz), while maintaining the structure of the wood. The process of ossification takes place under the ground, when a tree becomes buried under sediment, and may take millions of years. Ground water slowly seeps through the soil, turn off minerals where the lignin and cellulose rot. If the deposition and rotting go the same speed, the shape of the cells is maintained. The smallest details can be immortalized. Petrified tree rings and various tissues can be traced down to the microscopic level. Petrified wood has a hardness of 7 on the Mohs hardness scale, the same as quartz. The fossilization process has now returned to a laboratory for several days. Petrified timber occurs in a wide range of colors by varying the deposition of minerals such as manganese, iron and copper. Quartz is colorless, but when iron is added, creates crystals with a red or yellow hue, as is evident from the list below: Carbon - black Cobalt - green / blue Chromium - Green / Blue Copper - green / blue Iron oxides - red, brown, yellow manganese - pink / orange Manganese - Black Silica - white, gray. Repositories: Argentina: The Petrified Forest National Monument is seen in the Argentine Santa Cruz as one of the world's best preserved petrified forests; many petrified trees in Patagonia have a diameter of more than 3m and longer than 30 meters. Belgium: Geosite Gold Mountain near Hoegaarden * Greece: Petrified Forest in Sigri on the western tip of the island of Lesbos is probably the largest petrified forest, more than 150 km². There are strains up to 22 meters long. Large trees, complete with their roots, are still standing upright. Since 1985, it is a protected nature reserve. * Kerguelen: the French islands remains were found in petrified forests ninety million years old. * Namibia: The petrified trees near Khorixas are probably like tree trunks across rivers, from the north, fed to Namibia. Some recognizable strains are 30 m long. * Austria: in the state of Carinthia located at Laas remains of a petrified forest. * Czech Republic: The largest stone is located in the Nová Paka village museum and is 8.20 m long. * USA: The largest ones in the country get approximately 1.8 m in diameter and are therefore considerably smaller than those in southern America. A famous park is the Petrified Forest National Park in Arizona.