Dimensional stone is bought and sold on an unstated grading scale.  At the top of the scale is "grade 1," followed by "commercial quality," and then "grades 2,3, and 4." The grade of the stone is determined by the quarrier by onsite geologists and specialists who evaluate the blocks on a variety of factors including density, porosity, color, grain size, fissures and fractures, and its similarity to the "reference standard" of that particular stone.  Also, the quality of the cut, polish, and resin finish (if there is one) also get factored in the grading.  The block is then sawn into slabs and shipped to its final destination as a particular grade type. 

 

The quality of the stone is almost always directly related to its quarry position.  The deeper a stone comes from within a quarry, the older it is.  Which means it has been under greater heat and pressure longer.  This, in turn, affects its denisty and porosity.  To the homeowner, this means a more attractive, better wearing, and least absorbant (stain-resistant) material.

 

Better material yields better results and a cheap stone is well, a cheap stone.