Gems Notes and Extracts Augusto Castellani, Mrs. John Brogden 1871

108 GEMS.Now it is not much, valued ; nevertheless, in Italy,England, and Germany,it is used.Notwithstanding its rather soft . nature, it was,and is often, engraved. A great number are foundin various tombs. In that belongingto the Orleansthere was a cameo in peridot representing Cato.Crozat saw one on which was engraved a sibyl.The Abbe Pulini had in his collection a head ofMedusa beautifully executed on a peridot, remarkablefor clearness and good colour.LXXY1LPEARL.UNDER this name is understood in jewellery a concretionof carbonate of lime, round or tubercular, containingsome organic substance.It has a light peculiar to itself, and therefore calledpearly.It is generally of a milky- white colour, but issometimes green, red, blue, and yellow.Its specific gravity is from 2 084; in consistencyit equals all other calcareous substances, and, underthe action of a diluted acid, it changes into a gelatinoussubstance, but only on the surface, the inner partsremaining intact. It is formed of various pellicles,one over the other, in a similar manner to the onion.The pearl isnot a gem, but simply the productionof a secretion of some bivalve shell.