192 PHYSIOGRAPHY. CLASS ir. 



Fundamental form. Rhombohedron of unknown 

 dimensions. Vol. I. Fig. 7. Simple forms 

 II QD; R -f x ; P ; P + o> ; in various 

 combinations, as : R oo. P. P -f GO, simi- 

 lar to Fig. 112, &c. but possessing a tabular 

 aspect. Character of combinations di-rhombo- 

 hedral. 



Cleavage, R GO highly perfect. Fracture un- 

 even, scarcely observable. Surface, R QD 

 and P generally smooth or faintly striated paral- 

 lel to their edges of combination, the rest of the 

 faces rough. 



Lustre metallic. The highest degrees of lustre are 

 found upon R oo, both as faces of crystallisa- 

 tion and of cleavage. Colour iron-black, dark 

 steel-grey. Streak black, shining. Opake. 



Sectile. Thin laminae are highly flexible. Hard- 

 ness = 1-0.. .20. Sp. Gr. 2-0891, HAUY. 



Compound Varieties. Massive : composition gra- 

 nular, the individuals flat and scaly, of various 

 sizes, frequently impalpable. Of the latter, the frac- 

 ture is conchoidal or even. 



OBSERVATIONS. 



1. Tha division of the species Graphite into Scaly and 

 Compact Graphite, depends upon the size of the grain in 

 the compositions, the former comprehending those which 

 are still discernible, while in the latter they are withdrawn 

 from observation. The simple varieties have been either 

 united with scaly Graphite, or they have been considered 

 as a particular sub-species (Hoffm. H.B. IV. 2. S. 171.). 



2. The rhombohedral Graphite-mica consists of 



