676 DETERMINATION OF PRECIOUS STONES 



more frequent. The latter is characterised by its strong dichroism and the possession of 

 red as a second colour. Zircon, although doubly refracting, is practically not dichroic at all, 

 while demantoid differs from all three in being singly refracting. 



The only singly refracting stone in the second division is diamond. For the 

 distinguishing features of epidote, idocrase, sphene, and chrysolite the reader is referred 

 to the remarks appended to previous tables. Epidote, always of a rather dark green 

 colour, differs from the other stones in that one of the images it gives in the dichroscope 

 is of a dark brown colour. Under certain circumstances, however, it may be difficult to 

 decide whether a stone is idocrase or epidote. 



Diopside and chrysolite are sometimes almost precisely the same, both in colour and 

 specific gravity, and in such cases one has to rely on the difference in hardness. Chrysolite 

 is capable of scratching a crystal of diopside, but a cut diopside of course is not ; a crystal 

 of diopside may conveniently be kepb at hand for this purpose. Dioptase is always very 

 deeply coloured, and never perfectly clear. Fluor-spar is singly refracting. Apatite is 

 usually of a dark green colour tinged with blue. Andalusite and tourmaline are the most 

 strongly dichroic stones of this division, the former shows a characteristic red colour in the 

 dichroscope, and the latter a bluish-green. Both scratch quartz, while the distinctly but 

 less strongly dichroic hiddenite does not. 



The true emerald falls into Division IV. ; stones of similar colour, such as " oriental 

 emerald," hiddenite, and alexandrite, cannot therefore be mistaken for it. The specific 

 gravity of much fissured emeralds is lower than that of quartz, and such stones would 

 therefore fall naturally into division V. ; but this is never the case with faultless stones. 

 The true emerald, however, is sufficiently characterised by its wonderful green colour ; and 

 small variations in the specific gravity are of no consequence for purposes of determination. 



Moldavite, like artificial glass, is singly refracting, and is sometimes difficult to 

 distinguish from glass, although it is, as a rule, harder and less heavy. 



Alexandrite and green andalusite are very similar both in the colours of cut stones and 

 in those of the dichroscope images ; but besides the difference in the specific gravity, which is 

 considerable, there is a difference in hardness, alexandrite being capable of scratching 

 topaz while andalusite is not. Zircon is always recognisable by its strong adamantine 

 lustre and high specific gravity, which latter character distinguishes the stone from 

 diamond. Alexandrite, tourmaline, emerald, and moldavite, the green stones most 

 commonly met with, are sufficiently distinguished by their specific gravity alone, each 

 falling into a different division. The means whereby they may be distinguished from 

 artificial glass have been given already in the remarks appended to previous tables. 



B. TRANSLUCENT AND OPAQUE STONES. 



In the distinguishing of translucent and opaque stones, we are obliged to dispense 

 with the aid afforded in the case of transparent stones by the character of the refraction, 

 and to rely in a large measure upon the specific gravity. In dealing with opaque stones, 

 however, more use can be made of the character of hardness, since there is less fear of 

 damaging such stones by scratches. The translucent and opaque stones here considered 

 are classified, according to their colour and lustre, into eight main groups, each of which 



