294 SYSTEMATIC DESCRIPTION OF PBECIOUS STONES 



intensity of colour is as high as that of the finest sapphires. A not uncommon fault in 

 these stones is the existence of a peculiar, avanturine-iike, glittering appearance, probably 

 due to the presence of small enclosures. The appearance which gives their names to 

 star-ruby and star-sapphire is sometimes seen in " oriental topaz," which is then referred to 

 as " asteriated topaz " or " topaz-cat's-eye." Tavernier states that he saw among the jewels 

 of the Great Mogul an " oriental topaz" of 157f carats, which he valued at 271,600 francs 

 (^10,777). Another stone of this kind weighing 29 carats was in the possession of the 

 Parisian jeweller, Caire. It was remarkable for the Arabic inscriptions it bore, not engraved 

 merely on the surface but penetrating the whole thickness of the stone, and was probably an 

 Eastern amulet. 



" Oriental hyacinth. " (" vcrmeille orientale'") varies in colour from pale aurora- red 

 to reddish-brown. The presence of a pronounced tinge of yellow or brown makes its colour 

 very different from that of the ruby. This colour-variety of corundum is not an important 

 one ; it sometimes shows the sheen already mentioned as being present in " oriental topaz." 

 Its specific gravity of 4'0 distinguishes it from true hyacinth (zircon), the specific gravity of 

 which is 4-6 to 4-7. 



"Oriental amethyst" (violet ruby, " amethyst-sapphire " or purple sapphire) is 

 violet in colour and is of more importance than the last-named variety of corundum. Its 

 tint is often of a bright violet-blue, closely resembling the various shades of colour of the 

 true amethyst (a variety of quartz). Sometimes, however, its colour inclines to rose-red or 

 purple, and when this is the case the stone appears either like certain almandine-garnets or 

 like certain spinels. This stone, therefore, may be of almost any shade of colour between the 

 red of the ruby and the blue of the sapphire. It is distinguished from the true amethyst 

 by its strong dichroism, which is apparent even to the naked eye. The light which reaches 

 the eye along the axis of the crystal and out by one of the basal planes is of a warm violet 

 colour, while that which travels through the crystal in a direction perpendicular to this is 

 pale and almost colourless. This is a point which must be remembered when the stone is 

 cut as a gem, the lapidary arranging that the table is parallel to the basal planes of the 

 crystal, otherwise the stone will appear pale and insignificant. 



The " violet ruby," which by daylight always appears more or less red, has a still more 

 pronounced colour, and is even more beautiful by candle-light. Caire has described such a 

 stone, which was blue like the sapphire by day and of a fine purple-red by artificial light. 

 We may contrast with this the dull grey appearance of the true amethyst in candle-light. 

 The Maltese Cross, shown in Plate III., Fig. 8, is the form of cutting best suited to the 

 " oriental amethyst '' ; it is cut, however, in all the forms employed for other coloured 

 stones including ruby and sapphire. An " oriental amethyst " of a full deep colour is worth 

 approximately as much as a good sapphire. 



All the varieties of corundum hitherto considered are clear and transparent. Cloudy 

 and opaque corundum, when it possesses some beautiful feature, such as a fine colour, may 

 be cut as a gem. A case in point is that of adamantiue-spar, a semi-transparent, 

 hair-brown corundum, the basal planes of some crystals of which show, like star-stones, a 

 beautiful bluish-white sheen. When such a stone is cut en cabochon in this direction it 

 presents an appearance very similar to that of asteriated raby. China is considered to be 

 the principal locality for adamantine-spar ; it is also found at other places together with 

 precious and common corundum. 



