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        Ithout showing any prismatic effect, or allow</P>
                                </B>                        <FONT size=2></FONT><B>        <FONT size=3><P> real from an artifici</P> </B>        </FONT>
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                         with the excepti</P>                <P>stant and definite propo</P><P>pe (Chal</P><P> Ht, for when the direct rays of the sun fall upon it, the colours fade, and for a moment or two occasional phosphorescence follows, as is the case when the stone is warmed or heated in a dark room. The stone appears to be very susceptible to brilliant light-rays, and in certain specimens which were split for testing, one half of each being kept excluded from light for purposes of comparison, it was found that sunshin</P><P> aid, so that when the decision is made finally, there is never the least doubt about it. Rapidly as these tests can be made, they are extremely reliable, and should the stone be of great value, it is also subjected to other unerring tests of extreme severity, any one of which wo</P>
                                <P> Hibited under and amongst brilliant artificial lights. The mere fact that they are sold cheaply is _prima facie_ proof that the stones are glass, for it is evident that a diamond, the commercial value of which might </P>                <P>        Rated, the crystalline structure is specially perfect and unmistakable. It is doubly refractive, whereas spinel and the diamond, which two it closely resembles, are singly refractive. Topaz is readily electrified, and, if perfect at terminals, becomes polarised; also the commercial solutio</P> <P> action, and are so susceptible to their surroundings, that their purity and stability cannot be maintained for long even if kept airtight;
                                 consequently these ultra-perfect "imitations" are of no commercial v</P><P>Ay consider them just as good as the real gem, to the experienced eye they are readily detectable. By heating a sapphire its blue colour slowly fades, to complete transparency in many cases, or </P><P><img src="cid:98125589214633"></P>
                <P>Distinct cleavage. Its specific gravity varies from 4.70 to 4.88, according to the specimen and the locality. This stone, like some of the others described, has a very w</P>                <P>Self a variety, and these go through the gamut of greens, from a pale white green to the stronger green of asparagus, and through both the grey and yellow greens t</P>
                                <P>                        Ell selected and tempered, are not altogether reliable, especially in the more delicate distinctions of picking out the hardest of certain stones of the same kind, in which cases only the expert judge can decide with exactness. Accurate in this the expert always is, for he judges by the sound and depth of his cut, and by the amount and </P> <P>S is an important characteristic due to reflection, an</P>
        <P>Tical axis. _Polarisation_ is when certain crystals possessing double refraction have the power of changing light, giving it the appearance of poles w</P>                        <P>
                                Ertain means of testing stones and of distinguishing spurious from real. For if a stone is offered as a real gem (the true stone being known to lie in the highest or cubic system), it follows</FONT></P></DIV>        <DIV>
--Ston</DIV> <DIV> ce of c</DIV>
                                <DIV><FONT color=#40B69C size=2>                         a high tempe<BR>Nes have their colour improved by heat, by being tinged on the outside, by <BR>
                        d across and ov<BR>        <BR>
                Is called the oriental emerald. The oriental jacinth, or hyacinth, is a brown-red cor</FONT>                </DIV> </BODY>
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