I found it a couple days back in one of the ravines here on our farm. It's a cool piece. Our chert is very dark. When found in the creek it usually has the dreaded black skum - which makes location tougher.
It appears that my poor photography skills certainly do not help others to see details. I will try harder. Thanks for taking a look at this blade.
The rock in the background was found at the side of a large flat (20yds by 80 yds) limestone ledge that IS the surface in the creek for about 80 yds....a great lounging area?...I think the folks a few years before us used this relatively clean and smooth area with flowing water down the side to clean themselves, the kids, whatever was needing cleaned. The rock appears to me as a washing rock - I believe the "ridges" in the Sioux quartzite were installed to facilitate cleaning...careful now....this is the Sioux quartzite guy tossing out more crazy ideas!
Have a fun day!