Specific Chemical Composition of Nero Marquina Marble
To a first order approximation, the black stuff and white stuff are the same. Both are calcite (CaCO3).

The only information I could find online was that it contains some impurities of Mg (as dolomite maybe?) and of Al2O3. This shouldn't matter too much to you. The black stuff is black because it is very fine grained, and of organic origin. This is a limestone - made from millions of dead animals. The mass of the rock is their shells, made of calcium carbonate. However, you need just a little bit of organic material and heat, and it all turns to graphite. Graphite is an excellent material in making stuff black. Even a small percentage of fine grained graphite dispersed in the rock will make it black. The white stuff is pure calcite. Dissolved and reprecipitated in fractures as coarse grained crystals without any graphite or other impurities. That's why it's white.

I'm not sure what do you mean by "manipulating". This rock (as all limestones) is very sensitive to acids: vinegar, lemon juice, carbonated drinks, etc. Put it out in the rain for several decades and you will see the damage. It's also very soft. Unlike granite, which can hardly be scratched, limestone will be scratched very easily.