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 hy- 

 drophanous opal, among those substances which, from their lustre 

 resembling that of newly-broken resin, he distinguishes by the ge- 

 neric term of quartz-resinite. 



The analysis of Mr. Klaproth having been made, chiefly, with 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 probability 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. 



