356 Count De Bournon on BardlgUone, 



the height of which it has hitherto been impossible to determine, 



fig. 1. 



Integrant Molecule. The tetrahedral prism very distinctly exhibits 

 natural joints, parallel to the diagonals of its bases ; the integrant 

 molecule is therefore a right trihedral prism, having for its terminal 

 face a right angled isosceles triangle, fig. 2 : the height of the in- 

 tegrant molecule as well as that of the primitive crystal, which is 

 composed of four of these molecules, fig. 3,* is yet undetermined. 



Fracture. Even and shining in the direction of the cleavage; 

 but having commonly more lustre, and often a pearly aspect, on 

 those sides of the prism on which the cleavage is most easily ob- 

 tained. In every other direction it is uneven and granular; but 

 this latter fracture is rarely observed, from the facility with which 

 the fracture takes place in the direction of the natural joints. 



B. Physical. 



Specific Gravity. In very pure and transparent crystals from the 

 salt-works of Hall in the Tyrol, I found it to be 29,57, which agrees 

 perfectly with that stated by the Abbe Haiiy. 



Hardness. It scratches carbonate of lime with great facility ; but 

 is scratched, though with some difficulty, by fluate of lime. 



Refraction. Double in a high degree according to the Abbe 



* As my conclusions with respect to the primitive crystal and integrant molecule of bar- 

 diglione do not agree Avith what the Abbe Haiiy has said concerning them in his Tableau 

 Comparadf, &c. I have inserted, after the dctaLls relating to the several varieties of this 

 substance, the reasons that have compelled me to dissent from the opinion of that cele- 

 VfJvted mineralogist, foir whom I have the grea<test esteem, autl it-am whom I aever differ 

 \)\ii v/'ijtii cjtteme regcet. 



