420 PHYSIOGEAPHY. CLASS n. 



3. Pr. P. P -f oo. Figs. 3. and 4. 



4. P GO. Pr. P. (Pr I) 5 . P + OP. 

 (Pr + QD) 5 . Fig. 27. The three last varie- 

 ties from Ihlefeld in the Hartz. 



Cleavage, Pr + oo highly perfect, less distinct 

 P -{- GO and P oo. Fracture uneven. Sur- 

 face of the vertical prisms streaked parallel to 

 their edges of combination, often deeply furrow- 

 ed ; Pr streaked parallel to the edges of combi- 

 nation with P ; P QD parallel to those with 

 Pr ; Pr is often rough, the remaining faces ge- 

 nerally smooth. 



Lustre metallic. Colour dark steel-grey, iron- 

 black. Streak brownish-black. Opake. 



Brittle. Hardness = 2-5 . . . 3-0. Sp. Gr = 4-626, 

 crystals from Ihlefeld. 



Compound Varieties. Twin-crystals: face of com- 

 position parallel, axis of revolution perpendicular to 

 a face of Pr = 122 50'. Reniform, botryoidal, 

 and other imitative shapes : surface generally rough 

 and drusy ; composition columnar, of various sizes 

 of individuals, often forming a second granular 

 composition. Massive: composition granular or 

 columnar, the individuals of the latter of various 

 sizes, and often impalpable. In this case fracture 

 becomes uneven, or earthy. 



OBSERVATIONS. 



1. Grey Manganese-Ore has been divided into several sub- 

 species, chiefly in regard to its mechanical composition. 

 Radiated Grey Manganese-Ore comprises long acicular, or 



