A major aspect to consider is how hard a natural stone is. This is important in determining how much traffic it can support and where it can be used. The harder the stone, the less likely it will be to scratch.
Another factor is porosity, or how likely the stone is to soak up liquids. All natural stone tiles are porous and require a sealer to maintain their original look.
Tile sealers serve to protect and beautify your investment.
Check out our Tile Care section for more information. This is important to keep in mind since more porous materials require a higher level of care when maintaining a protective barrier from liquids.