230 PHYSIOGRAPHY. 



Thenardite. 



Color tin-white. 



Hardness (scale of BREITHAUPT) = 7-25 . . . 7-75. Sp. gr.= 

 6-74 . . .6-84. 

 1. It occurs at Skutterud in Norway. 



TETARTIN. (See Jllbite.) 

 TETRAD YMITE. 



Primary form. Rhomboid. P on P = 81 2'. 

 Cleavage, perfect at right angles to the axis. 

 Color lead-grey. 



In thin laminae, somewhat flexible. Hardness = 1-50 ... 20 

 Sp. gr. = 7-460 . . . 7-514. 



Compound Varieties. Twin- crystals. 



THENARDITE. Peritomous Brythin e-Salt. 



Primary form. Right rhombic prism. M on M = 125. 



Secondary form. 



1. The primary, having the terminal edges deeply re- 

 placed ; sometimes producing an octahedron with a rhom- 

 bic base. 



Cleavage, perfect parallel with the faces of the primary 

 form ; most distinct parallel with P. 



Lustre vitreous. Color white. Transparent. After 

 exposure to the light, it becomes coated with a white pow- 

 der. 



Sp. gr.=2-73. 



1. It is wholly soluble in water. 



2. Analysis. 

 By CORDIER. 



Sulphate of soda 99-78 



Sub-carbonate of soda 0-22 



3. It occurs five leagues from Madrid, and two and a half leagues 

 from Aranjues in Spain, at a place called Salines d'Espartines. It is de- 

 posited by evaporation, every summer, from a lake which holds it in so- 

 lution. 



