Archive for May 29th, 2015

Wooster’s Fossil of the Week: Petrified conifer wood

May 29th, 2015

1Petrified Wood 052615 585This is one of the most beautiful fossils in Wooster’s teaching collections. It is a polished section of petrified wood. It has vibrant colors and exquisite detail, as you’re about to see. Unfortunately any label that accompanied this specimen disappeared long ago. No matter how fantastic a fossil is, without its original location and stratigraphic context it has little scientific value. It works for our teaching collection, but I can’t tell you the age of the specimen, nor where it was found.
2Petrified wood close 052615 585Petrified wood is one of the most common types of fossil known to the public because of its abundance, attractiveness, hardiness (many a house out west has been built with petrified logs), and variety. Through the process of permineralization, minerals (quartz and chalcedony in this case) have infiltrated the porous organic structure, giving us three-dimensional, highly detailed preservation. This wood was first buried in low-oxygen sediments before it could decay on the forest floor. Groundwater circulated through the conductive tissue of the wood, depositing minerals in and around the cell walls of lignin and cellulose.

3Season of wood 052615 585It is hard to believe as we look closer and closer at the specimen that this is a fossil and not modern wood. Here we see the structure of the annual rings. The light-colored section is the new growth, the darker is when growth slowed at the end of the season. Our Wooster dendrochronologists, Greg Wiles and Nick Wiesenberg, could tell from this view that our tree was some kind of conifer.

4Polished petrified wood cells 585An even closer view of the same specimen. Now the perspective is dominated by vertical elements (rays) extending from the core of the tree outwards.

5Wood cells closest 052615 585This is as close as I could get with our photographic equipment. The cell walls and intervening rays are very distinct. Again, we’re looking at minerals here, not the original wood!

Again, fully label your fossils when you collect them. Because it has no locality information, this unlabeled specimen has little scientific worth. Too bad!

References:

Hickey, L.J. 2010. The Forest Primeval: The Geologic History of Wood and Petrified Forests. Yale Peabody Museum Series, 62 pp.