Species of hard Carbonate of Lime, &c. 337 
Its form is a perfect cube, the edges or solid angles of which 
are sometimes replaced by small planes. 
Its fracture is conchoidal : it has a smooth grain, with a small 
degree of lustre ; and, although it is impossible to make a regular 
fracture in any particular direction, yet the fracture shows that 
the crystalline laminae, or collection of molecules, are situated 
on the surface of the cube. 
Its hardness is rather inferior to that of the slightly attractable 
oxide of iron. 
Its specific gravity is very low; I found it to be only 3961. 
Its powder is more red than that of the slightly attractable 
oxide of iron, but has not the yellow cast observed in the powder 
of the haematite. 
To this species ought to be referred the eisen-glimmer of the 
Germans, w 7 hen it is not attractable : when, on the contrary, it is; 
attractable, it belongs to the slightly attractable oxide of iron. 
In the first case, this eisen-glimmer is in small laminae, which 
are very brilliant, but of an indeterminate form; and it fre- 
quently is found accompanying the haematites, and having the 
abovementioned appearance. If, in the formation of the haema- 
tites, some particles of the oxide of iron of which they are com- 
posed happen to contain a rather smaller proportion of oxygen, 
they naturally become the cubic oxide of iron here treated of. 
Indeed, some haematites, although they are crystallized in a very 
indeterminate manner, and are really of a species different from 
the cubic oxide of iron, show, by the colour and brilliancy of 
their surface, a tendency to approach towards it. 
When the octaedral very attractable oxide of iron (th efer 
oxidule of the Abbe Hauy) is in irregular and confused masses, 
the cubic oxide of iron here described is sometimes found mixed 
with it ; and, in that case, it renders the ore less sensible to the 
