Thanks to ASTROBLEME and Diamond Digger for the responses in my previous thread. I really do appreciate the time you've taken to answer some of my questions.

I still have many more questions, but I think I'll start with just a couple and some observations.

Is this what I'd be looking for as far as kimberlitic type material?



Most of it is very black until after it's been exposed to the weather, at that point a yellowish and in some areas a rusty red sort of film starts to form on the outer surface. It's very crumbly, I can break up a lot of it with just my hands, or a light tap or two with a hammer. Most of it is fine-grained, but there are chunks that look more like concrete, and then there are some with more of a crystalline appearance. It's fairly heavy and has a lot of iron in it. After breaking it up about 1/3 to 1/2 can be picked up with a magnet. I also have a lot of nasty yellow clay mixed in with the sand/gravel, which is quite different from the reddish brown clay that I'm used to seeing in this area. If you wash the sand/gravel with water you get a nasty yellowish muck that takes quite a while to settle. Is that what you guys refer to as yellow ground?