When buying a slap, you should be aware of various defects.
Cracks: Cracks can be found in natural granite. You can test this by pouring water, wiping and letting it dry. Water that goes into crack evaporates.
Grain Variation: the tiles and slabs should be sorted uniformly by grain size. The further you look and see it from the easier it is to sort.
Color patches: due to mineral localization there can be darker or lighter patches on granite. In black granite, there can be patches. These are permanent patches, which can look like oil had been spilled on it.  [More...]  [Selecting a Stone]  [FAQs]