An increasing number of cases of silicosis have been diagnosed in Spain in the last few years, reversing the trend of previous decades. Most cases have been found in marble masons because of the exponential growth in the use of quartz agglomerates as substitutes of marble. Quartz agglomerates are synthetic materials containing mainly quartz, but also other silica polymorphs (cristobalite and tridymite), which are considered more pernicious than quartz. The presence of different polymorphs of silica implies the need for x-ray diffraction (XRD) analysis for these to be distinguished, not only in bulk materials but also in respirable fractions from workplace atmospheres, as different threshold-limit values (TLVs) are established by Spanish legislation. For analysis of manufactured products, the Rietveld method allows the quantification of the mineral phases present in bulk materials from good-quality data obtained by XRD without the use of standards. Although it is known that high silica content in a bulk material does not necessarily mean high silica content in its respirable fraction, the aim of this work was to estimate the potential risk of quartz agglomerates by analyzing bulk samples and to evaluate the real risk for workers handling these materials by measuring their exposure to respirable crystalline silica. The Spanish National Silicosis Institute has analyzed in its laboratory a great amount of quartz agglomerate samples, corresponding both to workplace atmospheres and bulk material of manufactured products. A summary of the results obtained is presented here.