Gypsum[1] has a close affinity with limestone, and there are numerous varieties of it. One kind is prepared from a calcined[2] stone, as in Syria, and at Thurii, for example. In Cyprus and at Perrhæbia,[3] gypsum is dug out of the earth, and at Tymphæ[4] it is found just below the level of the soil. The stone that is calcined for this purpose, ought to be very similar to alabastrites,[5] or else of a grain like that of marble. In Syria, they select the hardest stones for the purpose, and calcine them with cow-dung, to accelerate the process. Experience has proved, however, that the best plaster of all is that prepared from specular-stone,[6] or any other stone that is similarly laminated. Gypsum, when moistened, must be used immediately, as it hardens with the greatest rapidity; it admits, however, of being triturated over again, and so reduced to powder. It is very useful for pargetting, and has a pleasing effect when used for ornamental figures and wreaths in buildings.

There is one remarkable fact connected with this substance; Caius Proculeius,[7] an intimate friend of the Emperor Augustus, suffering from violent pains in the stomach, swallowed gypsum, and so put an end to his existence.[8]