Petrified Wood a Curious Mineral
What Exactly is Petrified Wood?
Petrified wood is a type of fossil in which the organic material has been replaced by natural minerals but the original cell structure has remained in tact. The process known as petrifaction takes place when fallen plants and trees become buried under volcanic ash or sediment and are initially preserved due to lack of oxygen. As groundwater rich in minerals such as quartz, calcite, pyrite and occasionally opal flows over the organic matter it fills pores, spaces and other cavities. When the water dries up the minerals crystallize creating an internal cast. Whilst most of the organic matter decomposes, the cell walls often remain in tact and surround the newly formed crystals.
Petrified Wood Tumbled Stones
What's actually taking place to form petrified wood or fossilised wood as it's also sometimes known, is a process called permineralization and although different processes may vary slightly, the final outcome is pretty much the same. Permineralization is extremely slow and is believed to take at least 10,000 years from start to finish but there is some research to suggest that under the right conditions it may take place over a much shorter period of time. What is known for sure however is that the slower the process the more precise the replication and in some cases the petrified wood can be an almost exact replica of the original organic matter right down to microscopic levels. It's not unknown for ring patterns, bark and wood grain of the original tree to be clearly seen and in some cases the replication is so precise that the specific variety of tree can even be identified. It's sometimes believed that petrified wood is the original organic matter which has turned into stone but that is not the case, the organic matter is always replaced by natural minerals.
Petrified Wood Slices. Photo: Stone Mania ©
Petrified Wood or Fossilised Wood
The word petrifaction comes from Ancient Greek and literally means "wood turned into stone". Fossil comes from the Latin fossus meaning "dug up" or "buried". In English the word petrified is used to describe a situation where someone is paralysed with fear and were so scared that they froze. Petrified literally means to convert or change something into stone and comes from the Latin word "petra" meaning rock or stone. The origins of "fied" which is the latter part of the word is believed to have come from the Latin "facere" meaning to "make".
The terms fossilized and petrified wood are often used interchangeably and deciphering the difference between the two minerals is not easy. If this is something that interests you this forum discussion although from 2012 is well worth reading. Petrifaction is a form of fossilization but for purpose of simplicity the word fossilization is often used instead. What is clear is that not all fossils are reinforced or replaced with minerals but those which are do seem to be classified as petrified instead of fossilized. The definition of "fossil" according to the Oxford dictionary is "the remains or impression of a prehistoric plant or animal embedded in rock and preserved in petrified form". It defines "petrifaction" as "the process by which organic matter exposed to minerals over a long period is turned into a stony substance". Although any organism can be petrified, wood, bone and shell are the most common.
Peanut Wood Type of Petrified Wood
Peanut wood is a distinctive and unusual type of petrified wood that few people are familiar with. It's around 120 million years old and most of the world's current supply started life as conifer trees in Western Australia. As they died they were carried away by water ending up in the sea as driftwood where they were subsequently attacked by the teredo navalis. Also known as the naval ship worm, this species of saltwater clam has an appetite for boring through wood and has been an extremely destructive pest for as long as there has been wood in salt water. Once full of boreholes the driftwood sank to the ocean floor and the process of petrifaction began. Peanut wood gets its name from the distinctive light coloured round to oval shaped markings that are present in some form or another in this variety of petrified wood.
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