The granules can have various mineralogical composition, depending on the area of origin. Between the grains more resistant to abrasion and to chemical alteration, commonly abound those of the mineral quartz that, thanks to its resistance, is one of the most common constituents of these rocks . The granules are linked together by a cement, originated from the chemical precipitation of minerals formed by ions present in the water circulating in the interstitial pores.
Available in slabs and cubes.