wow that is one of the most awesome square pieces i have seen! I have dabbled in this stuff and it is a real challenge. there are some good books and vids by Waldorf on the subject. For those new to the topic- square cross section flintknapping was done in scandanavia and northern europe in the late neolithic and early copper age. axe bits were knapped and then ground down until the flake scars were 99% gone, and the axe head ended up looking kinda lie a steel one we'd use today. these were used to cut down trees, etc...
similar flintknapping techniques can produce a triangular cross section too- this is seen on the handles of some daggers from the same reigon and time period.
To me it seems thaf flintknapping , by it's nature, lends itself to creating the lens- shaped cross section we all know and love- so it's mind blowing in many ways that the ancient danes chose to make square and triangular cross sections. Even more so 'cos i'm Danish American!
search this forum for a few threads oin this. Look under " danish"