I dunno, but it sure is good looking. My b-i-law is geologist, and I could ask him, but anytime I try to ask him anything he looks at me like I am an idiot. I can't decide if I am asking idiotic questions or if he feels he is "off duty" and shouldn't have to talk shop on his own time. I of course assume it is the latter.

awesome rocks - i would love to put one of those biggies in my yard -

Well, I was a geology major as an undergrad (25 years ago) so I will take a stab. these fractures are just the natural way this granite wants to break....or cleave. Granite varies widely in its chemical/mineral composition and that will effect the cleavage planes (or lack thereof in this case). These look like conchoidal fractures (somewhat rounded, not parallel like you see in micas for instance). You see this in rocks with high quarts/silica content. Think of obsidian/volcanic glass (which is almost pure silica) and how it fractures....extremely conchoidal. It reflects the underlying matirx/structure of the atoms/elements of the rock. Hope that is clearer than mud.

Claire

Here is a link that might be useful: mineral fractures