PHYSIOGRAPHY. 



Thomsonite. 



231 



THOMSONITE. Orthotombus Kouphone-Spar. 



Primary form. Right square prism. 

 Secondary form. 



Fig. 433. 



M on d - 

 P on a - 

 P on c - 



135 00' 

 134 38 

 125 00 



Cleavage, perfect parallel with M, with P only in traces. 

 Fracture uneven. Surface smooth. 



Lustre vitreous, much inclining to pearly. Color white. 

 Transparent . . . translucent. 



Brittle. Hardness=5-0. Sp. gr.=2-37. 



Compound Varieties. Massive : composition columnar, 

 radiating from common centres. 



1. It intumesces before the blow-pipe, and becomes snow-white and 

 opake, but does not melt. 



3. It is found with Analcime in the trap rocks of Kilpatrick, near 

 Dumbarton in Scotland. 



