Dr. Thomson on some New Minerals. 



of which Mr. Alger was kind enough to send to mo. The colour of 

 the mineral is yellow, and it has the crystalline shape, and the char- 

 acters of chabasito so completely, that it would be considered as a 

 mere variety of that mineral, were it not that the constituents do not 

 quite agree. The specific gravity of acadialite is 2'0202, and its con- 

 stituents. 



Silica, .... 52-4 



100-4 

 The proportion of alumina in chabasite is greater than in acadi- 

 alite. If this difference bo constant, acadialite must bo considered as 

 a new species. Its constitution, and that of chabasite, may be repre- 

 sented by the formulas, 



Acadialite, 2 (AIS^ + Cal. S' + 6 Aq. 

 Chabasite, 3 (AIS^ + Cal. S^ + 6 Aq. 

 9. Prasilite. — To the next mineral species which I shall mention, I 

 have given the name of prasilite^ from the green colour by which the 

 only specimen which I have seen is characterized. It is found in the 

 Kilpatrick hills, and was brought to me some years ago by a gentle- 

 man while attending my class. He had picked up the specimen, and 

 brought it that I might tell him its name. On looking at and exam- 

 ining its hardness and texture, I pronounced it to be sulphate of lime, 

 tinged by an admixture of epidote ; but upon examining it chemically, 

 I soon discovered that the opinion formed from its external characters, 

 was erroneous. 



The colour is dark leek green, and the hardness not more than 1- ; 

 for it does not scratch selenite. It is opaque, and has a specific 

 gravity of 2*311 which comes near to that of selenite. It may be 

 crumbled to powder between the fingers. It is composed of fibres 

 very loosely adhering together. When heated to redness, it gives out 

 18 per cent, of water, assumes a light yellow colour, and becomes much 

 harder. Being subjected to analysis, its constituents were found, 

 Water, .... 1800 



90-70 

 The loss, amounting to 3 per cent., was probably an alkali. Prasilite 



