What is Petrified Wood? Petrified wood is fossilized remains of terrestrial vegetation. Petrified wood forms by gradual mineral replacement of organic materials as these materials are trapped underground. As rapid burial of these organic materials prevent natural decay, When this silica-rich water soaked into the trees, organic compounds in the wood were dissolved and replaced by very small crystals of quartz. This process of quartz replacing wood is called petrifaction.² The original cellular structure is obliterated, leaving just a cast of the original log or it may preserve rings, bark, knots, and cellular structure with extraordinary detail.
Petrified Wood in North Dakota. If you find it hard to imagine that during much of its geologic past North Dakota was covered by shallow seas, or more recently was buried under several thousand feet of glacial ice, then you will probably find it no easier to picture our state as densely forested. Yet during the Paleocene epoch, between about 67 and 55 million years ago, western North Dakota was home to a subtropical to temperate forest with trees up to 12 feet in diameter and over 100 feet tall. During this time, western North Dakota must have looked much like coastal Georgia or Mississippi, with meandering rivers, everglade-like swamps, and vast, forested floodplains.¹ Because of this, petrified wood is often spotted in western North Dakota and is commonly used as decoration in more urban areas or kept in nature and protected in more rural areas of the state. At ground zero of this EarthCache, the City of Williston has on display locally found petrified wood stumps. **Note that petrified wood can only be collected on private land with exclusive permission of the land owners. And it is illegal take petrified wood from any national parks or forests.
Colors & Textures of Petrified Wood. Most North Dakota petrified wood is brown or tan on weathered surfaces and dark brown in less-exposed spots. Small amounts of impurities add color to the fossilized wood: yellow, brown and red indicate iron; black and purple take their hue from carbon or manganese.¹ Petrified wood can also range in texture, from firm and well silicified to brittle and splintery. Petrified wood ranks between 7 and 8 on the Mohs Hardness Scale, making them still softer than Sapphire (9)³ but a lot more durable than a steel knife blade (5.1)³ and Agate (6.5-7)³.
To log this EarthCache: Answer the following 3 questions about the petrified wood at ground zero. Answers can be emailed directly to me instead of posted on your log. Failure to answer all questions will result in log deletion.
1. Describe as many colors as you can see of the petrified stump at ground zero?
2. Tree stumps in North Dakota 55 million years ago could be up to 12 feet in diameter. In any measurement (and using whatever/whoever you have with you), what is the diameter of the petrified stump?
3. Would you describe the petrified wood stump as well silicified or splintery?
Extra Credit: (Not required) Post a photo of yourself, your geocaching team, or your GPS/Signature item at the sign of this center. Do not include the petrified wood in your log image.
SOURCE SITE:
¹ https://www.dmr.nd.gov/ndgs/ndnotes/ndn3_h.htm
² https://home.nps.gov/thro/learn/nature/geologicformations.htm
³ Mohs Hardness Scale