( 273 ) 
2. NOTES ON THE SPECTRA OF THE PRECIOUS EMERALD 
AND OTHER GEM-STONES. 
By James Moir, M.A., D.Sc, F.C.S., F.R.S.S.Af. 
The spectrum of the true emerald consists of a broad pure-green trans- 
mission with three (new) very difficult hair-Hnes in the red. These are 
(a) and (b), a close pair near B, on the other side from the ruby-complex, 
i.e., facing C : the approximate wave-lengths are XX6805 and 6795 ; and 
(c) at about \6330 (very faint). There is also a very hazy wider band 
between these, round about C. 
The spectrum of Cr^O^ in a borax-bead contains a hazy band with a 
fairly sharp edge at X6800, so that the colour of emerald may be due 
to chromium : chromium glass does not show this band, nor do beads 
of vanadium or uranium show anything. Chromium acetate solution 
shows a similar band, but slightly displaced towards the yellow. 
The artificial emerald and the sapphire, either natural or artificial, 
have no hair-lines in their spectra. This is true also of the followino- 
coloured minerals which were examined : Rubellite, red spinel, amethyst, 
purple fluorspar, blue aquamarine, rose quartz, lepidolite, and topaz, and 
also purple titanium beads. Blue-green spinel has a broad band in the 
violet at about \4550 to X4600. The artificial emerald is merely a green 
sapphire (probably coloured with iron as well as titanium), and can thus 
be easily distinguished from the real emerald : wheras at present there is 
no satisfactory criterion between natural and artificial sapphires or rubies. 
The well-known almandine spectrum has been measured, as the wave- 
lengths do not seem to have been published : {a) Very faint, about X6150; 
(b) strong, X5750 ; (c) broad, about X5300 ; (d) strongest, X5070 to 5050 ; 
and (e) very faint and broad, about X4600. 
f 
