Hard ice is a new block added by RCcraft. It looks just like normal ice, but it doesn't smelt when you place it somewhere. Because it doesn't smelt it can be used as a nice building material. Hard ice is also used in Ice warrior dungeons.
This is how you craft it.
When you destroy it with a normal pickaxe it will drop ice, but when you use silk touch on it you will get the block itself back. You can also craft hard ice back into ice with this recipe.