]4 HINTS FOR OFFICERS IN THE DETECTION OF PRECIOUS STONES. 
treatise on mineralogy will show the different forms of crystals 
belonging to each system, and it is sometimes a valuable guide. 
Thus the stones picked up at St. Lucia by the C.R.E. were exceed- 
ingly perfect octahedra, of form of two four sided pyramids joined 
at the base. This at once showed that they were either diamonds, 
spinels, or garnets. They were scratched by sapphire, and scratched 
a garnet, therefore were white spinels. No further test was required. 
The experimenter is now in a position to identify any stone he may 
come across. I would recommend him to add to his tools a little 
hand-book, which weighs about 4 ounces, and contains a vast amount 
of interesting information on the composition, appearance, colour, etc. 
of all the stones used in jewellery. 
«Precious Stones, By A. H. Caurcu, M.A., Ere.” 
It is a “ South Kensington Art Hand-book,” published by Chapman 
and Hall. I think the price is about ls. 6d. 
With this to aid him, and the above mentioned apparatus, anyone 
with the least brains in his head would find that he could identify any 
transparent stone. He should especially search for the following, 
from a commercial point of view :— 
“ Diamond, ruby, sapphire, chrysoberyl cat’s eye, precious opal, 
emerald.” 
But really fine, flawless, large crystals of almost any stone but the 
topaz and the quartz gems would be worth securing. 
No white stone but the diamond is of much value, as the public look 
upon all such in the light of “ would be diamonds if they could.” The 
general public appear to be of opinion that any colourless stone mounted 
in jewellery is a diamond or an imitation, any red stone a ruby ora 
garnet, any yellow a topaz, any green an emerald, any blue a sapphire. 
An oriental topaz is no more like a yellow quartz “topaz” than a 
diamond is like rock crystal, but it is all the same to the public. 
There is one other instrument which is useful—though not at all 
essential—to the gem seeker. This is the dichroiscope. It is rather 
smaller than an Abney’s level. When a coloured crystal is double 
refracting—as all are except diamond, spinel, and garnet—it shows 
two colours, at least, when viewed with the dichroiscope. Table V. is 
extracted from “ Church’s Hand-book”’ aforesaid, and contains a list 
of some of the colours thus shown. Certain stones such as axinite, 
iolite and tourmaline are dichroic to the naked eye, the crystal showing 
different colours according to the direction in which it is examined. 
T will conclude by saying a word as to the buying of cut precious 
stones. If aman understands them he may pick up amazing bargains. 
A pawnbroker’s shop will often furnish old rings and brooches set 
with valuable stones, and sold for little more than metal value. I 
have bought a chrysoberyl cat’s eye in a rude Indian mounting for 
15s., and there is a queer old shop on the Dublin Quays where a queer 
old jeweller lives, who has cupboards full of stones and pastes and 
sells them at most reasonable rates. I think he has a large clientéle ; 
when I was last there, some five years ago, he showed me a fine opal 
