The Province of Buenos Aires produces more than 50 per cent of the stony aggregates used in construction in Argentina. Most of them, specially the sandstone rocks coming from the extreme SE of the Northern range of hills called Tandilia (Chapadmalal). The determination of the technical qualities of these rocks have been made through detailed field and laboratory determinations, that included physical, mechanical and microscopic tests, specific weight, absorption, simple compression, toughness, abrasion (Los Angeles and B. S. tests), durability and bitumen adherence. The results obtained concludes that this type of rocks, in all these tests, have a satisfactory performance. For that reason there are able to use in public works.