SYSTEMATIC DESCRIPTION OF PRECIOUS STONES 



The Mexican harlequin-opal is often remarkable for the variegated colours of its 

 surface markings. The variety known in that country as leehosos-opal is a beautiful fire-rect 

 opal with a magnificent emerald-green play of colour showing flashes of carmine-red and 

 dark violet-blue. Some stones show a reflection of emerald-green light combined with a very 

 fine dark ultramarine-blue. An opal with a magnificent rose-red play of colour was- 

 exhibited in Paris in 1887. These varieties vary in quality according to the place from 

 which they come, the stones from certain localities having quite a distinctive character. 



It would appear from what has been said as to the beauty of ,Mexican and Central 

 American opal and the abundance in which it exists, that the introduction of improved 

 methods of mining and of cutting the rough material would result in such an extension 

 of the opal-industry as to seriously reduce the trade in Hungarian opal. This, however,. 

 is not the case, for all opal from this region has a tendency gradually to become either 

 opaque or transparent, the play of colours in either case being more or less completely 

 lost. This feature, it is true, can be restored by soaking the stone in oil, but the 

 restoration is not permanent. Moreover, some of these stones have also a tendency to- 

 crack and fall into pieces in course of time with no apparent reason. When the.se 

 considerations are taken into account, it is not sui'prising that Hungarian stones are 

 preferred and that they fetch higher prices ; also it is obviously advisable to exercise 

 great care in the purchase of freshly broken Mexican opals. 



In the United States there is an unimportant occurrence of opal in the neighbour- 

 hood of the John Davis river, in Crook County, Oregon. The stones found here are 

 greyish-white and reflect red, green, and yellow light ; they are very similar to some 

 Mexican stones, but do not appear to exist in great abundance. In the American 

 continent it would seem that the abundance of precious opal decreases from south tO' 

 north, Honduras being richest in this stone, Mexico considerably less rich, and the 

 United States very poor. It was stated above that a great deal of the opal sold in the 

 United States as a home product is in reality Mexican in origin. 



Australia, especially New South Wales and Queensland, is an important source of" 

 precious opal. The stones, which are cloudy or milk-white, reflect light of the finest blue, 

 green, and red colours ; these colours are respectively disposed over larger areas than is the 

 case with Hungarian stones (compare Figs. 6-9, Plate XVI.). While in some opals different 

 areas of the surface glow with different colours, merging into each other, however, at their 

 margins, in other stones the whole area reflects light of one uniform colour. The difference 

 between Hungarian and Australian opals has jusb been pointed out; jewellers sometimes- 

 distinguish between them by referring to the latter as opaline. There occur also in Australia 

 many stones with the same distribution of colour as in Hungarian opals and equal in beauty 

 to the latter, but with a more decided tinge of yellow in the ground-colour. Many fine 

 gems have been cut from Australian opal which, at the present time, is more abundant in 

 the market than is the Hungarian mineral. 



In New South Wales the finest opal is found on Rocky Bridge Creek, Abercrombie 

 river, County Georgina, in a fine-grained, bluish-gi-ey amygdaloidal basalt or trachyte, which 

 has a thickness of 80 feet and is so altered that it may be scratched with the finger-nail. 

 The precious opal, which occurs only in small amount, is deposited in amygdaloidal cavities 

 or in crevices in the rock, and, as elsewhere, is accompanied by common opal and by 

 hyalite. The precious opal, which forms in every case only a small part of the opal 

 masses, is milk-white and reflects principally green, red, and rose-coloured light. 



The most important occurrence in New South Wales of opal of fine quality, and the 

 one exclusively mined, is at White Cliff's, on the farm Moomba in County Yungnujgra, 



