That is wild pyrite. Looks almost waxy.

The quarry exposes the lower Austin Chalk Formation.

Good question, Scott.
I didn't have to go far to look up the Austin Chalk Formation since Lance has some great pictures on his North Texas Fossils site. I was wondering if the wall in the middle picture, with plenty of free parking, was from an old quarry operation or was it just the way they developed the site?
You've done a great job on your site, Lance, thank you. I've been reading about the geology of the area and haven't gotten into the fossils yet, but intend to. Reading about the geology and hunting in areas like yours always makes me feel like I need some sort of submersible suit. Like 20,000 Leagues Under the Sea, or something. 
First question that pops to mind is do you ever come across any aboriginal lithic quarry sites while out fossil hunting? I know there's some fine knapping material in some of that chalk and limestone.