Earth Science Stack Exchange is a question and answer site for those interested in the geology, meteorology, oceanography, and environmental sciences. It only takes a minute to sign up.
Sign up to join this community
I'm looking to understand the chemical composition of the Spanish Nero Marquina Stone. Specifically, are the white veins of different composition than the black?
We are design studio pursuing work in this stone and are looking to deepen our knowledge of how we can manipulate it.
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.
The white veins are late stage crystallization products and are most likely pure calcite. As for the black matrix, almost all limestone contains a range of impurities such as clays and other silicates and/or a huge range of potential organics. I suggest that you powder some of the black matrix, dissolve it in acetic or hydrochloric acid, then filter or centrifuge the insoluble residue. Wash it a few times in distilled water, then dry. The inorganic components can be identified by X-ray diffraction. As a first indicator, you can check for organics by scanning the infra-red spectrum. Perhaps supplement this by a differential thermal analysis scan. Then you should have a good idea of what you are dealing with. In addition, you may wish to do a whole-rock analysis by X-ray fluorescence just to see if there happen to be any unexpected elements in the marble. For example, there is likely to be some Mg, Fe, Sr, Ba, Si, Al, and Mn.
