I can't say with 100% certainty if this extra large Paleo Uniface is a tan chert or a VERY hard cortex 'shell' from a Hornstone nodule. Where there are a few modern-made chips on the upper blade edge you can contrast patina--it's absolutely double your money back guaranteed authentic--try to get that deal somewhere else--you won't. Five years back, the piece went in my personal collection from the first Dr. Skaggs auction--the man had some fantastic Paleo, Clovis, etc...artifacts, but his recording system was almost nil when it came to pieces like this--add to that the auctioneers bagged up numerous pieces of varying cultures, sort of like they scooped things from a bucket and offered them as-is. The Doctor bought from southern Illinois, northern Kentucky, and in the counties along the Ohio River here in Indiana. If that's not enough provenance for you--I can't manufacture history that wasn't presented--what I can put forward is that the fresh chips LOOK like Illinois Mill Creek Chert. Length is a massive (for Paleo Uniface) 5&1/8" by 2&5/16"--at the 'peaked' center the thickness reaches almost 5/8"; blade edges are flaked in those very long Paleo characteristic flake scars--great workmanship. I welcome checks or M.O.s, but please note I do not use paypal--Roy A.