My grandkids are always collecting rocks for grandpa to make arrowheads with. Of course 90 percent aren't knapable but when they got back from vacation this fall they gave grandpa this bag of "rocks".
It's actually slag or something from Bay Furnace they found on the beach. Not the nicest shaped chunks to start with but really nice material would like to find a 50 lb chunk of this stuff to pound on for awhile. Not my prettiest point but considering what I started with I was pretty happy with the outcome
Bjrogg