Today I worked with Ian Bates and Lori Barkwill-Love at Round Mountain (AZ:CC:4:61 (ASM)) on Test Unit 4, which is a 1x1m unit just inside a terrace wall. When digging in Test Unit 4, we found this white chert core in level two of the unit at roughly 50-60 cm below the datum. What I found particularly interesting was that the exterior of the core was made of chert, whereas the interior was calcium carbonate. When rubbed with finger, the carbonate leaves a white residue much like chalk. In fact, chalk is a form of calcium carbonate however, I cannot confidently identify this object’s material as chalk. Calcium carbonate is a combination of carbon, oxygen, and calcium and is believed to have been formed indirectly due to an organism intrusion. An example may be a bacteria or a secreting organism such as a bug or ant. We all found this particularly interesting since a core is the beginning rock that is struck for the creation of stone tools, and although chert is a widely used rock for tool creation, calcium carbonate is rarely used for flaking stones for tool production.