Well, I'm going to break it into smaller pieces. From past experiences, there is a way to get it to break the way you want it but then it just doesn't look right. I used a drill bit to drill a hole through it, then a screwdriver and hammer, placing the screwdriver edge in the hole, and you get an almost straight vertical break. But it doesn't look right. And I also went through two drill bits doing this cuz they broke.
Getting it to break the other way is pretty easy, just use the screwdriver and hammer method along it's edge and it breaks apart easily. You don't get the shapes you want really, but it does make it to the desired thickness pretty much all the time.
With this lot though, I think I'm just gonna drop it and see what happens! Any other suggestions for breaking it up? I'm just gonna use whatever it gives me, i'll come up with something nice.
As for cleaning it, this stuff is pretty clean, a bit of dirt on it, but I don't think it was used for paving slabs or anything. Naturally, I'll boil the pieces to get rid of bacteria.
Although, would a microwave do the same job?