GeologyRocks

I haven't seen anything like it, but maybe it has to do with the cracks that go down the center of the leaf-like structures?  Maybe those cracks allowed something to travel out from that center mass and fill pores left in the sparrite in the area around the crack.

I see what you mean, but I'm not too sure. I'd assumed the sparite was a later cement fringing the object. I forget why now though. I'll have another look at the thing when I get chance, as the image quality is awful.

I have two possible options:

1. Replacement around cracks: there are four cracks that originate (or converge) in the micrite. Fluid along those cracks has re-crystallised larger sparite, giving the appearence of "leaf-like" structures. In other words it's a secondary (or tertiary) crystallisation
2. It's a group of bryozoans, their "stalks" connecting them and they've been slightly altered (very common)

Not sure which if these is more likely. Are there lot's of bryozoans in the slide (or any at all?)? Any other cracks within the sample that show alteration? Looks like an interesting slide though. Although I've been to Castleton a number of times, I've never looked at the reef under the microscope.

I don't recall seeing many bryozoans, but its a possibility! I'll have to have another look at the slide soon.