Gypsum2804 has a close affinity with limestone, and there are numerous varieties of it. One kind is prepared from a calcined2805 stone, as in Syria, and at Thurii, for example. In Cyprus and at Perrhæbia,2806 gypsum is dug out of the earth, and at Tymphæa2807 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,2808 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,2809 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,2810 an intimate friend of the Emperor Augustus, suffering from violent pains in the stomach, swallowed gypsum, and so put an end to his existence.2811