MR. J. T. HOTBLACK ON PRECIOUS STONES. 
23 
of igneous origin, but is the softest, or one of the softest, crystals 
used in jewellery, being easily scratched, and for that reason it is 
in small demand in this country, though sometimes of a beautiful 
deep colour, it is generally cut in steps, sometimes en cabocfu/n, but 
on the Continent it is often cut like a rose diamond, and set with 
a good foil. 
The value is so small that good specimens may now be bought 
at Is. to 10s. a carat, though a few years since they were worth 
much more. 
Tho next stone I propose to treat of is variously called kyanit, 
kyanite, and sappare ; its hardness is 5, and in the lateral planes 7, 
the S.G. is 3.55 to 3.G0, and Bristow gives the composition 
variously as : 
It will be noticed how the proportions are reversed. 
It occurs both crystallized and massive, generally in gneiss or 
mica slate. The colour is generally pale blue, but also white, grey, 
greenish, ami black. 
Sappare is the name given by French jewellers to this stone 
when brought ready cut and polished from India, where it has 
probably been sold as true sapphire. 
Though not held in much esteem, some specimens, by reason of 
their fine colour and play of light, may easily be mistaken for real 
sapphire, for which no doubt they are generally sold. 
The stones which I have enumerated so far, I believe all to be 
of igneous origin, and by that I mean that they have cooled and 
crystallized far down in the bowels uf the earth, and that when 
found in volcanic lava as garnets, chrysolites, and others sometimes 
are, they have been thrown there, and were not formed there. 
The stone I propose to treat of next, the idocrase, I cannot claim 
to have always so high or rather low an origin, as among other places 
it seems to be found at Vesuvius, in crystals of brown and green 
“ lining the cavities of volcanic rocks. - ’ It also occurs massive. The 
stone has a hardness of 6.5, S.G. 3.35 to 3.50, and I find its 
composition stated as: Silica 37.50, alumina IS. 50, lime 33.70, 
Kyanite. 
Silica 
Alumina 
34.33 
64.89 
Idocrase. 
