M, Beudaiit on the Opals Himgarg. 
in great request, and always maintains a high price : the small- 
est possible, when it is beautiful, does not go for less than four 
to five guineas ; and when the dimensions are large, the value 
augments altogether beyond proportion. There is a very beau- 
tiful specimen at Kaschau, of the size of a small crown-piecq 
{cfun petit ecu), for which 30,000 florins (or 79,000 francs) 
were offered. It is reported to have been purchased by the Ba- 
ron de Brudern, the present concessionary {concessionaire ac- 
tuel) of the opal mines ; but I have not learnt for what price. 
The iridescent colours presented by opal are not assuredly 
owing to cracks or fissures, as has sometimes been said ; for 
there is not tlie least appearance of fissure to be seen in the 
most beautiful specimens ; the smallest fragments into which a 
piece may be broken, present exactly the same play of light as 
the largest. This play of light is explained in a less forced 
manner, by the unequal distribution of vacuities, of different 
sizes, in which water is found inclosed ; it is easy, from the co- 
lours observed, to estimate the size, or rather the degree of mi- 
nuteness of these vacuities, proceeding upon the Newtoniaii 
theory of coloured rings. 
Ferruginous Opal also occurs pretty frequently in the same 
veins as the other varieties : it is impregnated with a greater or 
less quantity of hydrate of iron, which has probably been simul- 
taneously deposited, or into which the siliceous matter may have 
been subsequently infiltrated. Sometimes the appearance is 
that of a dull opaque opal, slightly coloured with yellow ; but 
we find, in the same nests, the quantity of iron augmenting by 
little and little, and often we find nothing but an opal-jasper 
{Opal Jaspis, Wern.) similar in every respect to those of which 
we shall speak afterwards, and which, from this circumstance^ 
appear to be true ferruginous opals. It occasionally occurs in 
large nests, in which the opal is no longer distinguishable, and 
to this variety are to be referred the specimens found arranged 
in collections, under the name of Opal- Jasper of Cseryenitza. 
Sometimes the iron becomes so abundant, that the opaline mat- 
ter discovers itself only by the resinous lustre which it communi- 
cates to the mass. This mixture takes place, as well in the iri- 
descent opal as in the other varieties : it is it which constitutes 
the black opal (that is to say liver-brown), v/hich it is extremely 
