I found a 2 inch diameter round rock in Oregon. When I hit it with a hammer it split it in half and there was a "seed" in the middle that had the appearance of an apple seed in shape, color, and size. I know that concretions start with a seed, but the inside pattern is not like any concretion I have seen. I goes out in "rays" from the center like a citrus fruit. What do you think it is? I sanded one of the halves.