6 Mr. R. W. Fox on Pseudomorphous Crystals of Quartz, 



quantity than both the others — nearly a tea-spoonful, and ob- 

 tained from only one crystal. It was very acrid to the taste, 

 and gave very copious precipitates when tested by muriate of 

 barytes and hydrocyanate of potash, showing the presence of 

 much sulphuric acid and iron. Oxalate of ammonia and ni- 

 trate of silver, indicated, moreover, the presence of lime and 

 muriatic acid. The saline matter in this water (mostly sul- 

 phate of iron) was equal to one-tenth of its weight; and if it 

 contained any common salt, of which I am not positive, the 

 proportion was very small indeed. Litmus paper showed an 

 excess of acid, the nature of which was not ascertained. 



Many of the pseudomorphous crystals are more than an 

 inch in diameter, and are partly or entirely filled with cry- 

 stalline quartz, whilst others are empty, or partly filled with 

 more or less numerous fragments of disintegrated fluor. I 

 counted nearly a hundred of such fragments taken from one 

 of the crystals or cavities, exclusive of many other very small 

 pieces. All the fragments are corroded, and indicate, by their 

 rounded edges and indented surfaces, the action of a solvent 

 which penetrated most readily between the planes of cleavage*. 

 Besides this disintegrated fluor, perfect octahedrons of fluor 

 occur in the same specimens; but they were rather more im- 

 bedded in the quartz and more protected from injury than the 

 others. Water was found alone in some of the pseudomor- 

 phous crystals or cavities, and in others it was found with 

 fragments of fluor, or with crystalline quartz. 



The most perfect pseudomorphous octahedrons occur within 

 large cavities of quartz. Some of the latter are more than 

 two inches in diameter, having the same form, and their sides 

 generally parallel to those of the former. 



The quartz specimens to which the crystals are attached, 

 present, when broken, the appearance of fortification agate, 

 having lines parallel to their structure of transparent and 

 milk-white quartz, differing in thickness ; these seem to indi- 

 cate that the siliceous matter had been deposited at intervals 

 of greater or less duration, or at least under different circum- 

 stances. After a time an entire change of conditions appa- 

 rently occurred in the vein, and octahedral crystals of fluor 

 were formed on the quartz ; then silex was deposited either in 

 a compact form, or in minute crystals, and coated the cry- 

 stals of fluor; afterwards fluor again appeared, forming octa- 

 hedrons over the others, and mostly with sides and angles par- 

 allel to them. These processes appear from some of the 



* When crystals of alum were kept for a time in water, the planes of 

 cleavage were first acted on, and fragments were separated from the crystals 

 resembling those of the disintegrated fluor. 



