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

48 GEMS.uncut diamonds; most frequently it is of a greyishwhite, and cannot acquire the diversified colours of thepure diamond, which it however exceeds in specificgravity. With us, it is only used to polish the regularlycrystallized diamond ;and for this purpose it ispounded in a mortar, and its dust, mixed with oil, andspread over a surface of soft iron, renders the frictionof the two diamonds more efficacious, and thus assistsin obtaining the polish and splendour of the differentfacets.It is known that, whatever the variations of certaincrystals, it is easy by means of their cleavage to reducethem to a regular determined form ;but in the knottydiamond this is impossible, as its texture does notpermit of cleavage.The knotty diamond is found in the mines of Brazil,whence they are sent to Europe.Some people say that the boost iscut and used bythe Orientals; but, even if this be so, they certainlyhave not in it a bright or valuable gem.XVII.CACHOLONG.A BARBAROUS name, not yet translated into any Europeanlanguage, and originating in Bokhara, from thewords of its dialect, each, river, cholong, stone ;that is," stone of the river." It belongs to the variety of theopal chalcedony opaque on the surface and of a milky;