60 PROCEEDINGS OP THE AMERICAN ACADEMY 



Biotite of South Burgess of Canada ; and the phenomenon of asterism, 

 seen so beautiful with the plates of the last, can also be seen with tliin 

 laminte of Hallite. It was impossible to free the mineral from this 

 admixture, but specimens Avere selected for analysis as free from it as 

 possible. It was also impossible to determine its exact nature. The 

 scales had not a definite form, but there was a tendency to a rhombic 

 shape, which is well described by the term " spear-shaped ;" and though 

 the material is so widely distributed through the crystal, the total mass 

 must be very small. 



This mineral is not so hygroscopic as Jefferisite, and no difficulty was 

 found in drying the material for analysis. When ignited, it exfoliates 

 like other species of vermiculite, but not nearly to so great an extent as 

 Jefferisite. After ignition it is decomposed by hydrochloric acid. The 

 specific gravity of the green variety, mean of four determinations, 

 2.398 ; that of the yellow variety, mean of two determinations, 2.402. 

 Before the blowpipe fuses with difficulty to a brown enamel. The 

 following analyses were made by Mr. C. E. Munroe, Assistant in the 

 Laboratory of Harvard College: — 



Green Variety of Hallite. 



* Trace of manganese. 



