Interesting rock

A couple of days ago we went for a little drive out to where the old airstrip was for our coffee break.  As I was wandering around, I saw this very cool rock:

It was a little boulder of boring grey, but was covered with what looked like kleenex that had been through a washing machine.  No, it wasn't bird poop!  I think they're called extrusions, they were white and a little bit sparkly.  Very cool, the sort of thing you usually ooh and aah at in the geology section of the natural history museum.  It's not that big, smaller than a volleyball.