Physical indices

In the sector of ornamental stones, the considered physical indices include the apparent specific mass, water absorption and apparent porosity. These indices define basic relations between mass and volume of the samples from a certain kind of rock.

The term "apparent", used for the specific mass (density) and porosity, indicates that the volume measured for the determinations is relative to the total volume of the analyzed samples, that is, the solid parts volume plus the volume of pores (empty spaces).

The apparent specific mass is expressed in g/cm³, kg/m3 or t/m3. The apparent porosity and water absorption are expressed in percentage, indicating respectively the total percentage of empty spaces in a volume of stone, and the percentage of intercommunicating empty spaces in this same volume.
However, the index of water absorption is never superior to the index of apparent porosity, noticing that a rock with high level of porosity does not have necessarily high absorption of water, because its pores and sockets may not be communicating ones.

The apparent specific mass and the apparent porosity provide indications about the physical and mechanical resistance of the rock, through compressive and flexion efforts. The water absorption index indicates the stone capacity of being soaked by liquids.

It is possible to draw from this procedure that there is interrelationship between the values of the physical indices. For instance, the smaller the density estimated for granites of one same lineage, the bigger will be the volume of empty spaces in the stone. The bigger the volume of empty spaces, the greater will be the apparent porosity and, possibly, the effective porosity. The bigger the effective porosity (that translates the existence of pores and/or intercommunicating sockets), the greater will be the water absorption expected for the stone and probably smaller its physical and mechanical resistance.

In short, the apparent porosity sample shows direct relation with the physical and mechanical resistance of the stones; the water absorption, with the possibility of infiltration of liquids; and, the apparent specific mass, with the aspects of physical and mechanical resistance, besides allowing the calculus of the individual weight of the specified plates, in the architectural project of a building construction.