32 



the geometrical outlines. The fracture is small, rather irre- 

 gularly conchoidal, and has a glassy appearance. Thumer- 

 stone is more or less transparent, breaks easily, is rather 

 brittle, may be scratched with difficulty by a knife, and 

 melts easily without addition by the blowpipe into a lightish 

 green glass. Spec. Grew. 3*113 — 3-300. 

 Analysis by Vauquelin : 



Silex 44 



Alumine . . . . . 18 



Lime 19 



Oxide of Iron ... 14 

 Oxide of Manganese . 4 

 Loss 1 



100 



The crystals are found in hollows in an earthy matrix of 

 itself, often having a fine Asbestus covering them which 

 looks like Clay, but may be easily detected by being 

 wetted, as it is composed of extremely fine fibres. I find 

 also some crystallized Carbonate of Lime with the 

 rhombic fracture. 



I am obliged to Mr. Penneck, Mr. Trevillian, ami 

 Mr. Rashley, for specimens. 



