Petrifaction
Petrified wood typifies this process, but all organisms, from bacteria to vertebrates, can become petrified (although harder, more durable matter such as bone, beaks, and shells survive the process better than softer remains such as muscle tissue, feathers, or skin).
This process occurs when groundwater containing dissolved minerals (most commonly quartz, calcite, apatite (calcium phosphate), siderite (iron carbonate), and pyrite),[2] fills pore spaces and cavities of specimens, particularly bone, shell or wood.
For silicification to occur, the geothermic conditions must include a neutral to slightly acidic pH[6] and a temperature and pressure similar to shallow-depth sedimentary environments.
[7] Pyritization is a process similar to silicification, but instead involves the deposition of iron and sulfur in the pores and cavities of an organism.
In marine environments, pyritization occurs when organisms are buried in sediments containing a high concentration of iron sulfides.
[3] Biotic remains preserved by replacement alone (as opposed to in combination with permineralization) are rarely found, but these fossils present significance to paleontology because they tend to be more detailed.
Built by ancestral Pueblo people about 990 years ago, this eight-room building was constructed almost entirely out of petrified wood and is believed to have served as either a family home or meeting place.
His methods were lost, but the bulk of his "pieces" are on display at the Museum of the Department of Anatomy in Florence, Italy.
have not been replaced by silicate, but have been infiltrated by specially formulated acidic solutions of aluminosilicate salts that gel in contact with wood matter and form a matrix of silicates within the wood after being left to react slowly for a given period of time in the solution or heat-cured for faster results.
[15] Hicks' recipe consists of highly mineralized water and a sodium silicate solution combined with a dilute acid with a pH of 4.0-5.5.
[16] In 2005 scientists at the Pacific Northwest National Laboratory (PNNL) reported that they had successfully petrified wood samples artificially.
Unlike natural petrification, though, they infiltrated samples in acidic solutions, diffused them internally with titanium and carbon and fired them in a high-temperature oven (circa 1400 °C) in an inert atmosphere to yield a man-made ceramic matrix composite of titanium carbide and silicon carbide still showing the initial structure of wood.
