578 



DETERMINATION OF PRECIOUS STONES 



distinguish them from bone-turquoise have been detailed under the special description 

 of that substance. 



Lapis-lazuli is always of a dark blue colour, which has sometimes a more or less 

 pronounced tinge of green. It frequently exhibits yellow, metallic specks of iron-pyrites 

 and encloses patches and veins of calcite. Its hardness and specific gravity readily 

 distinguish it both from the artificially coloured blue agate (" false lapis-lazuli ") and from 

 all the other stones of this group. 



Turquoise and lapis-lazuli are sometimes imitated in glass ; the means whereby such 

 imitations may be recognised will be found under the respective descriptions of these stones 

 in Part II. of this work. 



3. GREEN STONES. 



In Division I. malachite is recognisable by the fact that it efiervesces when brought 

 into contact with hydrochloric acid; it is also characterised by a peculiarity of structui-e, 

 being built up of curved concentric layers which are alternately lighter and darker. Ceylonite 

 is of a dark blackish-green colour, almost black in fact ; it is harder and heavier than any 

 other stone in this group. 



Nephrite and jadeite have figured already in Table 1. Chloromelanite is nothing more 

 than a ferruginous, and therefore rather darkly coloured and heavy variety of jadeite, 

 possessing otherwise all the features characteristic of that stone. 



Prehnite is intermediate in density between nephrite and turquoise, and floats in liquid 

 No. 3. It is capable of scratching felspar, but nephrite and turquoise are not. Nephrite 

 and prehnite are both characterised by a fibrous structure ; the green of prehnite has usually 

 a pronounced tinge of yelloM', while that of nephrite inclines more to grey. Turquoise, on 

 the other hand, is never fibrous in structure. 



The first four of the stones wJiich constitute Division V. of this group are all varieties of 

 quartz. Prase is of ii dark leek-green colour, and chiysoprase of a pale apple-green ; plasma 

 and jasper are of a pure green colour, which is always dark in shade. The colour of true 

 chrysoprase is so characteristic that it is difficult to mistake any other stone for it, except 



