Natural stone including granite, marble, and other stones are mined from the earth, and not all are the same. Unfortunately, the grading is inconsistent and vary from supplier to supplier. The top slabs will be called premium, designer or other designation. Lower grades are commonly called commercial , standard or builder grade. The lower quality stones may have carbon deposits that appear as black spots or patches and are generally accepted as undesirable. The lower grades will also have more muted coloring and less dramatic veining.
In the video below we asked a local stone supplier to show us the differences in color and veining.
Note the some of the most dramatic slabs include many fissures and even repairs and may be difficult to fabricate. Viens are impurities in the slabs which can cause weak spots along with the dramatic look. These slabs most likely need a lot more work to fabricate into long lasting countertops.
Some price-based fabricators will not disclose the grade of the slab and supply lower grade to meet a price. It is important you get good advice from a trusted source when selecting a slab for a countertop.