This specimen of petrified wood, more commonly called fossil wood, or wood opal. is made of almost pure silica, SiO2 in the form of chalcedony, opal, and quartz. Minor amounts of other minerals, such as iron, copper, manganese, etc. impart a certain amount of colour. Petrification occurs when wood is buried in water saturated sediment, which greatly reduces oxygen. Mineral laden fluids slowly replace the original wood in a process called petrification, preserving in fine detail the original structure. This specimen, although a mineral, is in reality a fossil. Origin is unknown. There is a comprehensive article on petrified wood in Silurian No. 1, which can be located elsewhere on this website.