I am not 100% sure on the proper implantation of the idea, but I was thinking something like this...
1. Either add natural occurring marble to the world that can be mined
or
2. And I like this one better, allow us to compress limestone in the compressor to create marble.
With the 2nd idea it would also add some use for limestone
Basically marble would be a block used mostly for building and aesthetic purposes.
Once you obtain marble you could add black dye to it to create black marble (optional of course)
The crafting recipes that I had in mind for marble are as follows:
M = Marble
- = Empty Space
-M-
-M-
-M- = Marble column, cylindrical column, optionally with some carving textures, can be stacked vertically.
- - -
- M -
MMM = Marble column base
MMM
- M -
- - - = Marble column top
M - -
M M -
M M M = marble staircase
Additionally, it could even be used for creating beacons.
M = Marble
C = copper cable
M C M
M C M
M C M = marble with cable running through it (coudlnt think of a name).
Stack the marble vertically and it would be able to transmit power to a light source (such as luminator) on the top, thus adding possibility of beacon or a lighthouse, whatever you want it to be