A few more things to consider in your decision process:
- How close to your building site is each product manufactured/extracted? The shorter the distance, the smaller the carbon footprint, which is a positive.
- What are the relative maintenance requirements of each product? The higher the durability and the lower the maintenance requirements, the longer the material is likely to remain installed. Nontoxic cleaning requirements are a bonus.
- With reference to the "raw" materials for each product, weigh these factors -- is the natural stone a byproduct of another raw material extraction process or is it virgin, and how detrimental is that process to the environment?
Although Portland cement typically has a high embodied energy factor, this negative factor can be partially offset if there is recycled content such as flyash in the mix.
In the end, you are generally better off choosing the material you like best, because you will be less inclined to tear it out and replace it in the near-term.
For more information:
Check GreenHomeGuide's "Buyer's Guide to Eco Stone & Tile" for pros/cons of many types of stone.