GEOLOGICAL SOCIETY. 



129 



EIGHTH ORDER— GRAMMITE. 



Not opaline. 



H. from 4§ to 9. 

 G. from 2, 2 to 3, 6. 



Brown streak : G. from 3, 2 to 3, 4, distinctly 



laterally cleavable, and H. 6| and more, 

 Tesseral : G. 2, 5 and less. 



H. from 4§ to 6 : rhombic, rhomboidal, distinctly 

 laterally cleavable, and G. from 2 9 8 to 2, 9, 

 as in tabular spar, Jam., and again from 3, 2 

 to 3, 6, as in electric calamine, Jam. 



H. from 7 1 to 8, and G. 3, 4 and more ; distinct 

 prismatic, or diagonal, but not half prismatic 

 cleavage of the first kind, as in disthen and 

 diaspor. 



H. more than 8 : distinctly cleavable, in one di- 

 rection, or in two, which cut themselves ob- 

 liquely, as in prehnite and pyroxene. More 

 examples are, willemite, pectolite, amphi- 

 bole, bahingtonite, bucklandite, sillimanite, 

 epidote, gehlenite, eudialyte, azure stone, 

 feldspar, edingtonite, scapolite and ambly- 

 gonite. 



Vol, 1— R 



