What causes the various dark areas on this Stone?

[Golfer]

What causes the dark areas in this Stone? Almost looks like it was decorated. Not magnetic. Found in same dirt pile dug near bedrock in southern New Hampshire. Really love searching to add to my collection.  Thank you. 

[FranzBernhard]

Could be caused by accumulations of black tourmaline.

Something in the line of that one:

Aplite with tourmaline (link to google image search results)

Franz Bernhard

[Golfer]

Thank you again Mr. Bernhard. I totally agree with your research.  Similar to granite but finer composition.  I have a lot more to find in the dirt piles.