People are often amazed when they pick up a piece of petrified wood, (p-wood) it can look like a bit of drift wood, say from a beach. When picked up, the weight is more like a solid rock. “What is this thing?” is a common refrain. The next question is, “How does it turn into a rock?” Petrified wood is a fossil or fossilized wood. When a twig, limb or a whole tree falls in the forest it is infested with bugs, fungus or other forms of rot. In a few years the tree is gone, now again a part of the organic mass of the forest, this is the normal cycle. Sometimes the wood falls into a swampy or muddy environment, the goo encases the limb and slows down the process of decay. In extreme cases, where the encasement is made up of silica or ‘hard mud’ (not a scientific term) the decay process can take many years, even thousands of years. As the organic cell structure decays a solution of mineral rich ground water fills in the void and deposits microscopic layers on top of each other, eventually forming a rock. This process is called petrification or petrifaction, the wood is then a fossil or fossilized wood. This fossilization is not limited to trees, most all organisms can become fossilized, even tiny microscopic stuff from squishy bacteria to vertebrates, think dinosaurs! 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. Petrifaction takes place through a combination of two similar processes: replacement and permineralization. These processes create replicas of the original specimen that can be accurate down to the microscopic level.
Google Image: Petrified wood you will get pages of beautiful photos of P-wood.
Now Google Image: Opalized wood, here you will find stunning pictures of wood whose cells have been replaced by opal, mostly common opal which is beautiful to behold, a lucky few have been replaced by true ‘precious’ opal. Some bits of opalized wood can sell for thousands of dollars. Petrified wood can also be from a ‘casting’ of the original limb.
Google image: Limb cast, to get a look at the many forms of this rock. Your search may also show you broken arm repairs, these you can ignore. In this process a twig falls into a solution, maybe a really hot mud flow during an earthquake or volcanic activity. The surrounding mud hardens and cooks away the original material and leaves an ‘impression’ of the original. The void is filled by mineral rich water and hardens over time to make a ‘limb cast’ This replica can be of twigs, branches or even smaller organics, like a tiny pine cone from millions of years ago. There are many colors of limb casts even a delicate pink that is semi-opaque.
Now search for dinosaur fossils; the images are amazing. Most of what we know about dinosaurs comes from fossilized remains of dinosaurs. Some finds are stomach contents preserved in great detail. In this way we learn what they ate, how they lived and what they may have looked like. There is even an arm of scientific study of the fossil record, paleontology. In the rock collecting hobby dino-bone is not rare, you can hold a piece of a real dinosaur fossil in your hand and marvel at the details. Some people feel strangely connected to that once living creature. Next consider the fossilization of dinosaur droppings, Coprolite, it comes in many colors and sizes, for some a major ‘YUCK’ factor. Like fossil bone, Coprolite serves a valuable purpose in paleontology because it provides direct evidence of the predation and diet of extinct organisms.
Bill Hanson is a Sonoma County native and a lifelong sportsman. He is the former president of the Sonoma County Mycological Association. Look for his column in The Community Voice each week.