The properties of tiles made of stone can include some of the same properties of ceramics, like coefficient of friction, porosity, and hardness, but they also have their own characteristics, like true color. In addition, tiles are given grade numbers that can mean something completely different, depending on the material of the tile. For instance, grade 1 ceramic tile is a fragile tile, whereas grade 1 stone tile is a high quality tile. Thus, to avoid confusion, we will only be referring to stone tiles when we discuss the characteristics of tiles in this simple guide. Here are a few characteristics that can help you pick the best tiles that will be suitable for your next remodeling project.
#1 Grade
Stone grades may only come in three choices, depending on the retailer's system. Typically, grade 1 is for premium quality stone tiles. Grade 2 is for tiles with minor defects like chips or scratches. And grade 3 is for tiles with major defects that will only make them suitable for decorative pieces. Since the grading system does vary from one retailer to another and can also refer to other characteristics, like size, shape, or tile thickness, it is a good idea to review the system and what it means at each retail outlet. However, sometimes, if a tile is ungraded, you can still know something about the quality via its reputation. In general, Calacatta marble is higher quality than Carrara simply because it is widely known that the veining is superior in Calacatta marble.
#2 True Color
Stone tile projects require a large amount of material in a uniform color tone. Typically, if you buy Noce Travertine tiles, you are looking for medium to rich dark brown tones, as that would be the true color associated with this material and its branding. If you see any green or pink tones, those tiles would not have a true color and can mess up your final project. Thus, you would want all your tiles to have the true color expected with the name associated with your tile color to get a uniform look, as in this Noce basketweave pattern.
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#3 Porosity
Porosity indicates the degree of pitting and divots you might have in the stone. It is also related to the absorption rating of a tile because the more porous a stone is, the more it will absorb water. Travertine, for instance, is more porous than sandstone, but less than granite. However, stones with a lot of pitting and irregular surfaces are valued for their textural aesthetic too, like travertine. Granite is non-porous, but it is also valued for being impervious to liquids. The irregularities in this type of stone make it perfect for outdoor pool settings.
#4 Hardness
A stone's hardness will give you some idea of the durability. The Mohs hardness scale will let you know the hardness of different materials. It is a scale from 1 to 10, with 1 being the softest rating and 10 being the hardness of diamonds. Granite is normally 6, which is a little harder than the medium. Thus, the higher on the scale a material is the harder it is and the more durable. So, if the tiles are rated with the Mohs scale, you can get a good idea of the quality of the tile too. In general, slate (between 2.5 and 4) is softer than marble and limestone (between 3 and 4 on the scale). Then, comes travertine a little higher on the scale, ranging between 4 and 5, and finally sandstone and granite, ranging between 6 and 7. However, this can vary from tile lots so if the lot has a hardness rating, take a look and see where it falls. If it is less than normal, it may be inferior quality tiles. Limestone makes a particularly nice choice in a bathroom, where it is water absorbent and softer on the bare feet than marble.
#5 Static Coefficient of Friction (SCOF)
Some people also refer to this particular characteristic as "slip resistance." The static coefficient of friction determines how slippery a tile is and can help you decide what material works best in the bath or around a pool. To obtain slip resistance, a minimum SCOF of .5 is prescribed by law. However, depending on the finish, you can increase the SCOF for travertine, from a natural .4 or .5 to .7, if the stone is textured or tumbled. The scale goes all the way up to 1.0. Just make sure the SCOF is taken when a tile is wet, and not dry, if your application is in moisture-prone areas, like a bathroom. Thus, travertine is a good choice for slip resistance. 
Waterjet Tile Tile - View Details>>
#6 Stone Textures and Finishes
Stones can come in natural, honed, or polished finishes. Texture can also be added through etching and engraving. Stone tiles are often sealed as well, against spills that can discolor their natural beauty. Consider where you plan on laying stone tile to determine whether it can be kept natural, sealed, or if it should be honed or polished. Keep in mind that honed and polished stone will be more slippery than natural, but that may be fine if the application is not on a floor. This bathroom used waterjet porcelain, stone, and metal tiles to add an elegant texture.
Porcelain Waterjet Tile - View Details>>