This week’s WoW is a beautiful example of how the natural processes of fossilization and diagenesis* can sometimes create breathtakingly unique and intricate pattern formations. This fossil is a rugose coral, found in Jeffersonville, Indiana and collected by R.D. George in the early 1900s. The numerous concentric rings detailing the fossil’s surface are not representative of the true external surface the rugose coral once exhibited in life, but instead are a form of Chalcedony called Beekite. This type of mineral forms as a result of the specific set of conditions under which the coral was fossilized and it is often seen on specimens from the Paleozoic Era.
In life, this rugose coral would have had a skeleton made of the mineral calcite. During the fossilization process, its original calcite skeleton was replaced by silicate minerals, a type of fossilization referred to as Silicification. The type of silcate that normally replaces an organism’s original calcite skeleton during this process is plain old Silica (think glass). The organisms are essentially preserved as glass. You can see some of this amazing silicification type preservation in fossil from the Permian Reef Complex in the Guadalupe Mountains National Park, Texas.1 There are many examples of silicified corals in this deposit and you can see many of them in situ on a hike of the Permian Reef Trail.
In the case of this rugose coral, however, the silica has taken on a different crystalline form during the fossilization and diagenesis process, it forms Chalcedony and appear as this unique pattern of concentric rings on the external surface- Beekite. The term Beekite was named after Henry Beeke, an 18th century British historian and naturalist. Beeke is credited with bringing attention to the mineral formation to geologists of his time. Geologists have studied how this type of mineral forms during the fossilization process and one recent hypotheses suggests that the beekite rings form when the supply of silica is limited during the period when the original calcite of the organism is being dissolved.2
While one person may look at this simple rugose coral and consider how the Beekite design was formed, another may simply marvel at the Earth’s natural artistry. The existence of life on Earth is a complex consequence of every molecule’s interaction with another, and the effect of that interaction on yet another, and so on, and today’s Beekite-adorned fossil exhibits that concept beautifully.
* Diagenesis is the set of processes that occur early in sedimentation, after something is buried but before it has become a fossil (if living) or metamorphic rock (if non-living).
1. https://www.nps.gov/gumo/learn/nature/geologicformations.htm
2. https://www.cambridge.org/core/journals/geological-magazine/article/abs/preservation-of-shell-microstructure-in-silicified-brachiopods-from-the-upper-cretaceous-wilmington-sands-of-devon/E82DB094AA68C69E527304B43EB69CA7