Newbie questions - Lime Rock vs Dry Rock

[GuppyHJD]

Walking through a local landscaping nursery with my wife and I see a pile of "lime rock". It's 3"-6" pieces of "rip rap" - pieces of lime rock with shells and pieces of coral imbedded. This rock looks smoother and lacking all the nice places for bacteria to grow. Will it work as base rock?

 

[rwreef]

Probably raise/create ph issue with tank. Also, yes not great for surface area. I would avoid.