While there is no industry standard for quality when it comes to marble tile, there are some ways you can watch out for lower quality materials. Learning what makes a marble stronger, what makes it weaker and when these factors matter can help you choose the right material for you tile design.
Flip the marble tile over and look at the back. If the back of the tile appears to be covered in a mesh or net, this marble is more fragile than others. The mesh is fiberglass resin and is used to reinforce the stone against cracking or breaking. This marble may not be as suitable for high traffic applications, not because it may crack, but because it may scratch or etch more easily.
Examine the surface of the marble under a light, holding it at a 45-degree angle. If there are small, dull patches on an otherwise polished surface, the marble may have "fill" in small holes or fissures in its surface.
Some stones, such as Thassos White marble, will only have fill in the lower grades; the higher quality stones have no holes that need to be filled with epoxy or resin. Stones with fill that is not a good match in color to the stone, or stones that have large amounts of fill should be avoided. The fill may come out over time, leaving a hole in the stone that the homeowner will need to patch to prevent further damage.
Examine the marble for veins on its surface and then flip the tile over to see if there is a crack, or fissure in the same place on the back of the stone. Some stones, such as Crema Marfil, are very prone to fissures and may be likely to crack if the fissure is deep enough. Small fissures are common in some stones and for wall use or low traffic areas will not effect quality or use.
Ask for the marble's complete name. Thassos AAA, for example is a higher quality of stone than standard Thassos. Also ask for the marble's hardness factor. If a stone has a high hardness factor, yet seems to have fiberglass resin, fill or fissures, this is a poor quality tile of that stone. A stone with a lower hardness factor may have these qualities present without it effecting the stone's overall quality or use.