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

52 GEMS.the cause of the difficulty that exists in distinguishingit from the onyx agate, which it much resembles.It ismuch harder than this stone, but the difficulty of determiningthe degree of hardness without testing thestone prevents the possibility of deciding whether agiven substance be really calcedonyx, except by thelapidary who tests it on his wheel.Barbot is said to have determined the specific weightof this substance, which according to him is 2'6180.It is often even more translucent than agate.It appears that it came from the East, and was notonly known to, but engraved by the ancients, andthese engraved stones are the only specimens in existenceof the calcedonyx, as, at present, none is foundin any part of the world that we are aware of.In the ancient collection of Genevosio, Caire saw anengraved calcedonyx, representing a warrior seated oppositea dead body. In the Viennese cabinet of engravedgems there is another, which represents a youngman leaning on a column.XX.CARBON.Bv this name, of which every one understands thegeneral signification, we would specially indicate, technically,a mineral substancediscovered in Brazil in theyear 1812, which was found mixed with deposits ofdiamonds in alluvial lands and in the mud of rivers.