354 
detached spots will be frequently seen on them, in the neighbour- 
hood of the opal, presenting an appearance, very nearly resembling 
that which would be produced by the spread of a fine resinous 
varnish. I should have been much more disposed to hesitate, in 
thus opposing Mr. Kirwan, on a mere object of sense, if I had not 
been supported by one of the latest authorities, on such a point, 
the Abbe Hauy, who places the opal, the semi-opal, and the hydro- 
phanous opal, among those substances which, from their lustre re- 
sembling that of newly-broken resin, he distinguishes by the generic 
term of quartz-resinite. 
The analysis of Mr. Klaproth having been made, chiefly, wfith a 
view to the ascertaining of the nature and proportion of the earths, 
contained in the substances he examined, the first part of his opera- 
tion was, generally, ignition, in an open crucible ; by which the water, 
and other volatile matters, must have been indiscriminately dissi- 
pated. Such was the mode in which he made an examination of 
the brown-red semi-opal of Telkebanya; and even thus a circum- 
stance occurred, which did not escape his nice observation, and 
which tends strongly to evince the j)robability of this semi-opal 
containing a portion of that matter, on which I presume the pecu- 
liar lustre of substances of this class depends. Mr. Klaproth was 
surprised to find, on igniting this substance in the clay crucible, 
that its whole surface was covered with a fine scaly ferruginous crust, 
of a metallic lustre, and attractible by the load-stone. This, Mr. 
Klaproth says, is, indeed, an unexpected phenomenon ; and is the 
more remarkable, from the iron, so strongly oxided, as it is in this 
fossil, being thus reduced to the reguline state, so as to obey the 
magnet ; and this, without any admixture of charcoal, or any other 
substance of a nearer affinity with oxygen*. If I were constrained 
to rest the support of the opinion I have formed on any single ex- 
* Analytical Essays, p. 449. 
