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

140 GEMS.How long does Nature take for this operation?This can never be determined.Wood petrifies into silex, agate, and chalky substance.The bushes which surround the so-called Layo delTartari, which is in the Tibertine territory, petrifyfrom year to year.It is not long since a beam of timber was foundunder the bed of the Danube ;it had been used in theconstruction of the Emperor Trajan's bridgeover thatriver, and it was found that in 1,500 years it was onlypetrified |ths of an inch from the circumference towardsthe centre.Agate wood has a concave and rough breakage;acquires a resinous light it cuts ; crystal, and has aspecific gravity between 2*53 and 2-65.This substance is sometimes opaque, at other times itis transparent, but more frequently translucent.It is easily worked as its texture yields to every tool ;it is therefore used in making vases, snuff-boxes, knifehandles,and seals.It is generally worked in Germany, and in the sameway as the agates of Oberstein,itLYII.LEPIDOLITEIs a sort of mica with a base of lithia, thus namedfrom the Greek ACTUS, scale, and XiOos, stone, because,in general, it is found under the form of small pebbles,