ZIRCON 



The other forms shown in the 



341 



figures 



are those assumed by common 



termination, 

 zircon. 



Zircon has a very imperfect cleavage, scarcely observable in fact; its fracture is 

 distinctly conchoidal. The mineral is harder than quartz but softer than topaz, its 

 hardness being represented on the scale by 7^ ; this is not very great, but is sufficient to 



h. o. 



I'IG. G8. Crystalline forms of zircon. 



admit of a brilliant polish, so that an artificially polished facet, like a natural crystal-face, 

 shines with a brilliant, adamantine-like, vitreous lusti-e. The specific gravity is very high ; 

 it varies between 4-610 and 4-825, the mean value for the hyacinth variety being 4"681. 

 Zircon is thus denser than any other precious stone, heavier, indeed, than any mineral not 

 containing the heavy metals (lead, silver, copper, &c.) in large amount, and when placed in 

 the heaviest liquid it quickly sinks. 



Zircon may be cloudy and opaque, or clear and transparent. The opaque, common 

 zircon is usually brown or grey in colour, sometimes between green and black, and is little 

 used as a gem. A fire-red, cloudy zircon, called after its place of origin " Ceylonese zircon," 

 is sometimes cut as a gem. Precious zircon is not always perfectly transparent ; in such 

 cases the stone, though markedly translucent, is still pleasing in appearance by virtue of its 

 brilliancy and lustre, which is comparable to that of the diamond. Zircon is only rarely 

 perfectly colourless and water-clear ; crystals answering this description occur implanted on 

 chlorite-schist at Wildkreuzjoch, in the Tyrol, and also in Ceylon. More frequently it is 

 green, brownish-red or brown, and sometimes violet ; but by far the commonest tint is a 

 brownish shade of orange resulting from a mixture of red and yellow in about equal 

 proportions. The latter colour inclines in some stones more to red, and in others to yellow, 

 and some are dark and others lighter in shade. Zircon of this colour, which is known as 

 hyacinth, and is practically the only variety commonly cut as a gem, is represented in Plate I., 

 Figs. 11 and 12. Transparent green zircons, like the one illustrated by Pig. 13 of the 

 same plate, are sometimes cut as gems, as are also the reddish-brown, brown, and violet 

 varieties. It is only exceptionally, however, that these latter are sufficiently transparent for 

 this purpose, and when they are, they are sometimes mistaken by dealers for tourmaline. 



The reddish-yellow colour characteristic of hyacinth is known as hyacinth-red. The 

 same colour is seen in cinnamon-stone or hessonite (Plate XIV., Figs. 7 and 8), a variety of 

 garnet which occurs in association with hyacinth in Ceylon. So much alike are these two 

 gems that hessonite is often sold by jewellers for hyacinth ; indeed, it has been stated that 

 practically the whole of the so-called hyacinth bought and sold in European markets is in 

 reality hessonite, although this stone is far inferior both in brilliance and lustre to the true 

 hyacinth-red zircon. The means by which the two stones may be distinguished will be 



