Can anyone identify what this rock is?

it looks like you have some sort of evaporite deposit (salt of some sort, perhaps some sort of sulfate or hydroxide) on top of the regular bedrock material. the bluish superficial crust might be some sort of lichen or bacteria or something. There could be some sort of dissolution-precipitation reaction happening at the surface: there is a fairly clear irregular line of contact which would be consistent with water infiltration leading to superficial mineralogical change (a sort of alteration).

It is difficult to tell from the photo, but having been to DV, I would guess it is a boulder of limestone/dolostone showing karstic weathering. Some of the oldest rocks in DV are blue-grey limesones/dolostones.