TOPAZ: COLOUR- VARIETIES 331 



tourmaline, which occurs in Brazil in association with white and blue topaz. Bluish-green 

 and greenish-blue topaz is so very similar in appearance to aquamarine, that a careful 

 examination is sometimes necessary in order to distinguish between them. The difference 

 in specific gravity is here a valuable aid ; in pure methylene iodide topaz sinks, while 

 aquamarine floats. Topaz bearing this resemblance to aquamarine occurs at various 

 localities, but specially in the district about Nerchinsk in Siberia, and when cut is always 

 passed oft" as aquamarine. True aquamarine is more abundant and more widely distributed 

 than is topaz, especially topaz of this particular colour, so that here we have the very 

 unusual case of a rarer mineral substituted for one less rare. The dichroism of blue topaz 

 IS most apparent when its colour possesses a tinge of green, and the greatest contrast 

 between the two images of the aperture of the dichroscope exists when one is practically 

 colourless and the other almost pure green. In the case of aquamarine, the two images are 

 coloured yellowish-white and clear sky-blue respectively. Topaz of a yellowish-green 

 colour like chrysolite is rare ; the typical colour of the mineral is the one we are now about 

 to consider, namely, yellow. 



Yellow topaz exists in a great variety of shades, ranging from the palest possible 

 shade of pure yellow up to dark brownish yellow, usually tinged more or less with red. 

 Yellow topaz is the only variety which is recognised by jewellers as topaz ; it is by no means 

 always of the same tint, and stones showing different shades of yellow differ in value and are 

 distinguished by special names. 



A fine saffron-yellow topaz, the so-called Indian topaz, occurs in Ceylon, not, however, 

 in abundance, and as a great rarity in Brazil. Very beautiful topaz of a dark yellow colour, 

 tinged with red or brown, occurs in great abundance at the Brazilian localities. A crystal 

 of this description is represented in Plate XIII., Fig. 2, while Fig. 2a illustrates a faceted 

 stone of a somewhat different tint. Topaz of gold-yellow, honey- yellow, wine-yellow, and 

 other shades is also found in Brazil though in less abundance ; the gold-yellow variety is 

 distinguished as Brazilian topaz. 



Saxon topaz is of a pale wine-yellow colom* ; a crystal of this variety is illustrated in 

 Plate XIII., Fig. 3, and a faceted stone in Fig. Sa. It occurs at Schneckenstein, near 

 Auerbach, in Saxon Voigtland. Occasionally it is tinged with green, and is then known as 

 " Saxon chrysolite.'''' 



The dichroism of dark yellow topaz is fairly \vell marked ; the two images of the 

 dichroscope aperture being coloured respectively light and dark yellow, or yellow and red. 

 The paler the stone the less marked is the contrast in colour of the two images, and with 

 quite pale yellow stones the difference is scarcely apparent at all. 



The stones which are most likely to be mistaken for yellow topaz are yellow sapphire, 

 the so-called "oriental topaz," and yellow quartz, the so-called citrine or " occidental topaz." 

 The latter exhibits the same fine tints and is often substituted for topaz. The fraud may 

 be easily detected by the difference in the specific gravity of the two minerals, just as 

 rock-crystal is distinguished from water-clear topaz. The difference in specific gravity 

 enables us also to distinguish " oriental topaz " from true topaz in the same way that 

 colourless sapphire is distinguished from colourless topaz. 



Topaz of a pronounced red colour occurs in nature but rarely. It is met with 

 occasionally in Brazil associated with crystals of a yellow colour, and is usually of a light 

 rose-red inclining to a lilac shade of colour, very similar to the colour of " balas-ruby." In 

 spite of this resemblance the two gems need never be mistaken the one for the other, since 

 the " balas-ruby " (spinel) is singly refracting and not dichroic, while topaz is dichroic and 

 doubly refracting. This variety of topaz, a crystal and faceted stone of which is represented 



