360 DR T. THOMSON on Asbestus, Chlorite, and Talc. 



4. Asbestous Rock, from the Island of Bernera. 



The colour was light green. The mineral was composed 

 of fibres, having some breadth, and running in general longi- 

 tudinally, though rather irregularly. When examined by a mi- 

 croscope, it appears to consist of white and green coloured fibres 

 alternating ; the lustre of the green fibres being glassy, and 

 that of the white silky. Perhaps these appearances may be 

 owing to different sides of the fibres presenting themselves to 

 the eye. 



Scratched by the nail. 



Opaque, or nearly so. 



Feels rather harsh to the touch. 



Streaks white. 



Specific gravity 2.984. 



On being subjected to analysis, its constituents were found 

 to be as follows : 



Silica, 56.430 



Magnesia, .... 23.256 



Lime, 13.636 



Protoxide of iron, . . 4.098 



Alumina, . , . . . 0.516 



Protoxide of manganese, 0.280 



Moisture, 0.250 



98.466 



