The quartz sand in the CÇu ThiÒm area belongs to marine sediments of the Phó Bµi Formation (Q₂^1-2pb). The sand bodies are of large size, their average length is about 5 km, the width - about 1400 m and the thickness of 3 m, locally up to 6 m. The quality of sand is very good: the content of SiO₂ is very high, about 99,34% in average; the content of Fe₂O₃ is very low, about 0,03 in average and the content of alkaline oxide is also low. The grains of sand are homogeneous; the fraction of 0,1-0,5 mm occupies more than 80%. So the quality of quartz sand in CÇu ThiÒm is high, and they can be used in high quality glass production, pottery and frit enamel.