28 PHYSIOGRAPHY. CLASS i. 



tion = 8 0', in the plane of the long diagonal. 

 Vol. I. Fig. 41. R. G. 



a : b : c : d = 19-10 : 3472 : 13-66 : 1. 



Simple forms. - (P) - 79 41' ; (Pr + oo) 3 (M) 



- 7fi W . + P r _ -f p i_ 



3 ' - -163 28'> ' 



5' ; Pr -}- OD ; Pr + oo (7). 



Character of Combinations. Hemi-prismatic. In- 



clination of P QD to ?r -f OD = 93 0'. 



-p 

 Combinations. 1. _. (fr + co) 3 . 



2. ?. (Pr + OD) 3 . Pr + oo. Fig. 45. 



/v 



3.?. Pr 1. ?5. (Pr + cc) 3 . Pr + o>. 



ft-S ?. (Pr + oo) 5 . Pr + oo. Pr + oo. 



ft 



Cleavage. , distinct ; Pr + co imperfect ; traces 



si 



of (Pr + oo) 3 . Fracture conchoidal. Surface 



smooth and even. 

 Lustre vitreous. Colour white, the grey and 



yellow tints are owing to foreign admixtures. 



Streak white. Semi-transparent. 

 Sectile. Hardness = 1-0 ... 1-5. Sp. Gr. = 1-423. 



Taste pungent, alcaline. 



Compound Varieties. Several imitative shapes : 

 composition columnar. Massive : composition gra- 

 nular. Commonly occurring in the stale of powder. 



