When choosing high-quality natural stone, there are a few things you'll want to look for:
1) Carefully choose the selection, or aesthetic, of the stone.
Is the background mottled? Or is it pure, with nice even veining?
2) Understand the material grade.
This refers to the soundness of the stone, or how well it has been manufactured, which affects how easily it can be fabricated and installed.
A Grade A material, for example, shows fewer cracks, fissures and veins, or has been expertly filled or reinforced by the factory. Therefore, the material is less likely to break upon shipping, handling and installation.
A Grade D material, for example, will be one in which cracks and fissures are prominent. In some instances, these will be filled properly with resin or cement to increase its quality. In other instances, the manufacturing does not meet necessary standards. It’s important to know the difference and it’s extremely important to understand that not all materials are the same, even if they have the same name.
3) View the stone.
Whether you are purchasing slabs or tiles, make sure you view them prior to purchasing. Order a sample, or – if you’re buying slabs – try to view them in person. Natural stone countertops are often the focal point of the project. And since each is, by nature, different – you’ll want to know what you’re getting.
4) Look for quality in manufacturing
What is the dimensional consistency? Are tiles consistent in size from piece to piece? Make sure you know before you install. (Note that the TCNA, Tile Council of North America, standards for tile manufacture allow for some size variation from one tile to the next. This is standard with all tile.)
Look for tiles that are squared and properly beveled. Tiles should be cut at a true 90 degrees and have consistent edges. (Note that some artisanal tiles will not be perfectly rectified, and that’s by design.)
5) Understand the range selection.
All natural stone, and many man-made materials such as porcelain tile, vary from piece to piece. With stone in particular, it’s best to view multiple samples prior to purchase, so you can understand some of the range or variation in the material. (Note that even samples won’t show all characteristics in the stone, so always anticipate variation in your final product.)
When purchasing stone such as marble, quartzite or granite for countertops, ensure they’re properly resin and vacuum processed. When done properly, this process adds strength and stability to your material.
And finally, always inspect the material at the project site prior to installation and always seal natural stone prior to use.