Unmet promise - broken arrowheads from western Concord, MA

For the first hour I was finding arrowhead fragments at a rate of one per half hour. But this did not continue and I gave up after another half hour. Each fragment looked like it could be something:

 

I could not make sense out of this quartz one.

 

But this is a black felsite triangular Brewerton missing a tip and a corner. The field definitely is worth checking more.