Amorphism of Solid Bodies. ^^^ 



are to be regarded as fine granular crystalline masses. If this 

 were the case, we should obtain another view of opal, as it could 

 then be regarded as a crystalline fine-granular member of he 

 quartz series, although much ^vould still remain^obscure. It is 

 in fact not to be denied that there are varieties of calcedony and 

 flint which have much resemblance to opal, so that one is often 

 doubtful whether to refer them to the opal or to quartz But 

 the supposed passage is nothing else than a mixture of these 

 minerals, of the calcedony and flint, with opal, whereby the 

 whole becomes more shining and acquires a higher degree of 

 transparency, because the crystalline portions of quartz are sur- 

 rounded by opal. It appears to me probable, that if not all, yet 

 certainly almost all, calcedonies and flints are penetrated by a 

 larger or smaller quantity of opal ; and this I conclude to be the 

 case from the result of the following experiment. A flat cut 

 portion of calcedony, which had a pale bluish-grey colour, and 

 was strongly translucent, was placed in moderately concentrated 

 hciuid potash, and left there in a well closed glass. As I i;e- 

 marked no change during four months, I believed that it would 

 not be acted on, and paid no farther attention to it At the end 

 of nine months, however, I again looked at it, and found it whUe 

 and opake. I left it some time longer, but could perceive no 

 further chano-e. At the end of a year I took it out of the liquid, 

 ,n order to examine it more attentively. It had lost 3.9 per cent, 

 of its wei-ht, was, however, nearly as smooth and shining as 

 previously, but, except in some slender stripes which were not 

 previously to be remarked, and which probably consisted of pure 

 quartz, was perfectly opake, and resembled much the mineral 

 called cacholong. In the potash there was silica wh.ch nearly 

 amounted to the loss of weight of the calcedony Thus was this 

 calcedony proved to-be a mixture of quartz and opal, which lat- 

 ter was extracted by the potash, and it is thus rendered extreme- 

 Iv probable that the cacholong belongs not to the opal but to 



the quartz. „ 



Flint would, doubtless, if subjected to the same process, a - 

 ford a similar result. The white, dull, and opake portions, which 

 arc not rare in this substance, are very probably nothnig else 

 than extremely fine granular quartz or flint, without opal The 

 mixture of opal is probably the cause that flint is suited to its 



