Anyone know what this is?

I don't know much about Croatian geology, but that looks like it might be man made to me. It also looks faintly blue in the photo's. Is it actually blue or is it more grey in real life?

Does it feel like cement, or some type of solid rock?

It's not blue. It probably looks like that because i turned on flash when i took photos.
http://i.imgur.com/W9t8kxN.jpg
http://i.imgur.com/0kYY5BH.jpg
It feels like cement.

My guess would be that it's man made. Do you live close to any old construction sites or demolition sites or anything? Maybe it's a chunk of concrete with an old re-bar penetration or something.