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This post is about a fossil look alike, or to quote my kid, "a foss ilarm". Earlier this year I was scratching my head about stromatolites, stromatoporoids, and algae and coral in general. It started with finding what I dubbed "the sandwhich rock" (first 3 pics) at a roadcut in Blair County, central Pennsylvania (US). The outcrop is Mifflintown-Bloomsburg (undivided). My best guess is this form the Mifflintown part. Friends that know their stuff told me about "honeycomb weathering". Besides the Wikipedia article, there is more than I ever wanted to know in the Treatise on Geomorphology Volume 4, Weathering and Soils. I returned to the site and took more photos. This outcrop is on a very busy city highway and just below a freeway overpass. I wanted to know if the weathering is just from modern-day exposure, so I poked at the rock layer until I found a piece that was still in place, but loose. To my surprise, it was olive brown and pitted like this all the way around, even the back side which had not been exposed to wind/sun. I removed that piece and cracked it open.... and was even more surprised to find the inside of the rock is light grey with brachiopods and broken trilobite bits. it failed the vinegar test (no fizz). The inside of the rock looked untouched, to my noobie eye. And that makes me think that all this pitting is from very recent time. In my superficial reading, I've seen frequent references to salt as a common factor in weathering. Even though the backside of the rock was still really pitted (R side of pic with my fingers), there is probably a lot of highway salt that makes it way into the soils and float on the face of the outcrop. Is it a player? Beats me, I've gone as far as I can thinking about this. Except to note my extreme-environment microbiologist wife always likes to say "microbes rule all!!"

For those interested in Ediacaran fossils, you may have seen a lot of supposed medusoids coming out of sandstones/quartzites in Namibia. They are usually labeled as unidentified medusoids, but sometimes as the enigmatic genus Namacalathus to command a higher price. At first glance, some specimens do bear resemblance to a top-down cross section of Namacalathus (such as the specimen below), however note that Namacalathus are preserved as calcite skeletons, not as molds in sandstone. A thread discussing these was posted several years ago, without a definitive conclusion. As far as I can find, there have been no published articles on these so called fossils, and perhaps rightly so. After a recent trip to the Field Museum, I am fairly confident that all of these specimens are simply the result of weathering in sandstone. Here is the specimen at the Field Museum that piqued my interest. A quick scan of our favorite auction site will reveal a number of nearly identical specimens listed as medusoid fossils. These holes are likely what are known as tafoni, defined by Wikipedia as "small (less than 1 cm (0.39 in)) to large (greater than 1 meter (3.3 ft)) cave-like features that develop in either natural or manmade, vertical to steeply sloping, exposures of granular rock (i.e., granite, sandstone) with smooth concave walls, and often round rims and openings." They have various methods of formation, but the more "Namacalathus"-looking specimens look (at least to me) to be the result of iron nodules rusting out. They may also be several tafoni that overlapped. Here is an image of tafoni in sandstone from Namibia. (image credit Wikipedia) Regardless of the exact process of formation, I am confident in saying that these are not fossils. There are plenty of other Ediacaran fossils out there for purchase, and given the high price tag these pseudofossils seem to command, I hope this post helps collectors avoid wasting money.