Poros stone

[1] There is no precise definition of the term, although its roots go to antiquity,[2] when it was used to designate any porous building rock,[3] regardless of its origin,[4] mostly in contrast with marble.

In the 20th century the archeologists continued to use the term in the similarly loose way: "poros [was] made to include almost all light-coloured stones" that were not definitely marble or hard limestone.

The ease of working with poros is the reason for its extensive use as a building stone, especially for foundations and other architectonic parts that are not exposed to view.

[2] The Greek geographer Pausanius uses the term "poros" to describe the material of the Temple of Zeus at Olympia, which was built of local shell limestone, Theophrastus (and Pliny the Elder, who borrows the description) declares it to be a less dense variant of Parian marble.

[5] Henry Stephens Washington (a geologist with a major interest in classical studies) declared in 1923:[2] [A] non-petrographic archaeologist [while in Greece] will not go far astray if he calls by the name of "poros" any [...] easily cut, finely granular, yellow, light cream or gray, dull-lustered and somewhat rough building stone, which effervesces with dilute hydrochloric acid or with acetic acid [...] and usually leaves a fine muddy residueWashington describes the differences between poros and regular limestone as the former being very finely arenaceous or marly; most often of a pale cream color, also light yellow or light gray; somewhat granular but rather soft and friable and easily cut with a knife, especially when first exposed in the quarry (similar to the volcanic tuffs of Roman Campagna in this last quality, while having nothing in common otherwise).