Green on the outside, clear on the inside?

I fished out a few of my marble sized stones today and crushed them. For the first time they weren't green all the way through, but they got lighter as it got closer to the center. They all were clear in the middle and they all came out at different times. Not exactly clear, but the color of wax that doesn't have any color added to it. Anyone run into these? Any ideas why they are clear in the middle? Just curious.

This was a good flush but not a great one. I didn't get any tans stones this time, but I have been using the GCG, I suppose the tan ones may have become sludge. I think I got better results using the olive oil. Now that I've proved that the green stones don't come from the olive oil, I'll probably go back to it.

bd