The Italian stonecutters know slate under the name of Lavagna, because the largest quarries of this stone are near the citadel of Lavagna in the Genoese area. Brard 85 assures us that in the region indicated there are forty-three fully working quarries. Mineralogists call it argillaceous schist. The colour is generally of a brown that verges on black, but there are dull reddish or dull greenish ones. It is formed of flat, thin continuous strata, that are easily separated into sheets and flagsstones, and in this state it is very resonant. It does not effervesce with acids and barely takes a mediocre polish. It is used in many ways, but principally for covering buildings, and as drawing-slates. When it is very compact and very hard it is called whetstone, or hone, being well adapted for the sharpening of razors.
560. (139.1) Marmor Thebaicum, Lavagna antica. This stone, which is found in excavations of Rome, has a blackish brown background, very much marked with small yellow spots regularly placed, and it is of a slaty nature. Pliny 86 says that 'Theban stone is mottled with droplets of gold, is found in a part of Africa assigned to Egypt, and has a certain usefulness as whetstone on which to grind natural collyria'. Collyrium was a medicine that used to be prepared to treat eye conditions. Dioscorides 87 in referring to Theban stone called it blackish and dull. If the specimen which I am discussing is compared with the descriptions given by Pliny and Dioscorides, there could be no doubt that the stone called by the stonemasons lavagna antica would correspond perfectly with Theban, as much in colour and markings, as for its formation and nature as a whetstone. (Very rare).
562. (140.3) Lavagna di Genova. Entirely grey verging on black. This is the Lavagna slate. (Common).
563. (140.4) Marmo polveroso di Pistoja. This stone is blackish and monochrome. It is called dusty because over the black ground it has a colour verging on grey resembling a covering of dust. (Rare).