ORDER VIII. RHOMBOHEDRAL IRON-DUE. 407 



impalpable, sometimes very distinct and easily se- 

 parated ; often, however, they are strongly cohe- 

 rent ; if they are impalpable, their lustre decreases, 

 their colour becomes red, and the fracture even, 

 uneven, or flat conchoidal. 3. Lamellar, joined 

 in the face of R oo, thick and variously bent ; 

 sometimes, however, they are so thin that they 

 allow blood-red light to pass ; if they are still 

 thinner, their colour becomes red altogether, and 

 their lustre imperfect metallic : the faces of com- 

 position are often irregularly streaked. When the 

 cohesion among the particles is diminished, the la- 

 mellar varieties become scaly and glimmering, the 

 granular ones earthy and dull. Pseudomorphoses 

 in the shape of rhombohedral Lime-haloide, octa- 

 hedral Fluor-haloide, &c. 



OBSERVATIONS. 



1. There can hardly be a more striking example of the 

 necessity of correctly ascertaining the simple and com- 

 pound state of a mineral, than that afforded in the species 

 of rhombohedral Iron-ore, even in regard to the correct 

 determination of the species itself; for the two species of 

 Specular Iron-ore and Red Iron-ore entirely depend upon 

 this composition. Its importance extends likewise to the 

 determination of the genus ; for the connection between the 

 octahedral, rhombohedral, and prismatic Iron-ore, cannot 

 be rightly understood if we do not pay attention to the 

 simple or compound state of their varieties. Specular Iron- 

 Ore contains all the simple varieties and those of the com- 

 pound ones, which have not yet lost their metallic appear- 

 ance by the too small size of their component individuals. 

 Those in thin lamellar compositions have been called Mi- 



