PRECIOUS OPAL: OCCURREiNCE IN HUNGARY 379 



lie at four or five different levels one above the other, have a total length of four and a half 

 miles, and the hill is penetrated by an adit. The workings are excavated by preference in 

 •a conglomerate of andesite blocks, possessing great hardness and solidity. The miners, of 

 which in 1877 there were 150, loosen the opal-bearing rock with great caution, and carefully 

 free the precious material contained in the detached fragments from the mother-rock. On 

 the same spot there are also cutting works, which find employment for six men ; the stones 

 are worked with emery on a leaden disc. There is a tradition that in the year 1400 no less 

 than 300 persons were employed here in the mining of opal ; even if this number be not 

 •exaggerated the yield would probably be less than it is at present with fewer workers but 

 better tools and methods. 



The yield is very variable, and depends to a great extent upon a fortuitous combination 

 of circumstances. Not infrequently precious opal may be searched for in vain for a distance 

 ■of 10 or 12 yards. Large specimens are now very rare, and several years may elapse 

 between the finding of specimens of the size of a hazel-nut. Some of the large specimens 

 met with in former times are exhibited in the collection of minerals preserved in the 

 Imperial Natural History Museum at Vienna. In this collection is to be seen the largest 

 known specimen of Hungarian opal ; it is uncut, but quite free from the mother-rock, and 

 exhibits a most beautiful play of colours. It is wedge-shaped in form and about the size of 

 ^ man's fist, being 4| inches long, 2 J inches thick, and J to 3 inches high; it weighs 

 ■34 loths or nearly 600 grams (about 3000 carats). An Amsterdam dealer in precious stones 

 is said to have offered for this fine opal half a million florins (^"25,000) ; it has been valued 

 -at 700,000 florins, but Partsch in his guide to this collection (1855) values it at 70,000 florins 

 only, and this has been copied into other works. The specimen was found in the seventies 

 •of the eighteenth century near Czerwenitza. A smaller stone, also remarkable for its purity 

 and magnificent colour, of the form and size of a hen's egg, is perhaps a portion of the 

 above-mentioned specimen ; it is preserved in the Imperial Treasury at Vienna. 



Another extensive find has more recently been made, namely, at the end of the eighties 

 •of the nineteenth century ; in this case the opal occurred as a large mass, not as small nests 

 ■as it usually does, in the andesitic mother-rock. The mass measured 15 metres in length 

 and 20 centimetres in thickness ; it consisted for the most part of milk-opal, but in two 

 places was intersected by precious opal of fine quality and bordered here and there with the 

 ■so-called oculus, that is to say, opal with a less brilliant play of colours. This particular 

 occuiTence was also remarkable in that the play of colours instead of being disposed in very 

 ■small patches and spangles, as is characteristic of Hungarian opal, occupied large patches of 

 the surface as in Australian opals. The difference in the appearance of opal from these two 

 localities will be understood on comparing Figs. 6 and 7 with Figs. 8 and 9 of Plate XVI. 



Besides pure opal, mother-qf-opal is also mined in Hungary. This term is applied to a 

 xock containing specks of precious opal of greater or less size, but always too small to be 

 worth isolating from the rock in which they are embedded. The dark mother-rock flecked 

 with the bright prismatic colours of the opal forms a material which can be applied very 

 ■effectively to many decorative purposes, and when the flecks of opal are numerous and 

 ■close-set, mother-of-opal may even be used in jewellery. The eff\;ctiveness of the stone is 

 .sometimes further enhanced by soaking the alw.-iys more or less porous mass in oil, and 

 afterwards exposing it to a gentle heat. The matrix is much darkened by this treatment 

 and consequently forms a better background for the flecks of precious opal, which are 

 unaflected by the process. It is possible that the black opal mentioned above is produced 

 by similar treatment ; nevertheless, there is no doubt that black opal does occur in nature, 

 though very rarely. 



