Ken, that's Sonora flint from Kentucky. It comes in nodular form and is quite scarce. It only occures in a very small area in Hardin county Ky and that area has been picked over heavily for 30 or so years. These days, if you spend a day looking and come away with a 5 gallon bucket full of hunting point size pieces, you done well...very well.
It's good rock, but hard to get.
