I split my working time between steel and marble.
Breakthrough cubes came about as an endeavour to make an incredibly fragile piece which would show off the beauty of the marble. I left the block as a framework to hold the marble 'membrane'. I used a particular Portuguese Pink marble which has a bit of pink veining but is otherwise quite white.
Horizon Splitting is made from chopped up and welded together angle iron, something I have been doing for ages, twenty-five years and more.