Supposed New Mineral Species. 



359 



Figures 1 and 2, however, represent the usual forms of the 

 mineral ; and it is a somewhat remarkable circumstance, that it 

 appears to be as rare at these localities, under a compound or mas- 

 sive form, as it is under regular crystals at Phillipstown and Gren- 

 ville. 



Fig. 1. Fig. 2. 



The edges of the crystals are generally sharp and well defined. 

 The faces also are flat, though considerably pitted, from a natural 

 incompleteness in part, but still more from imbedded minerals, as 

 apatite, zircon, pyroxene, plumbago, &c. It must not be consid- 

 ered, therefore, that the angles above given, will be found inca- 

 pable of correction. They are, however, the averages of numer- 

 ous trials, the limits of variation were generally within 40'. 



No very marked difference in lustre is perceptible on the dis- 

 similar faces of the crystals, if we except c and b, which are both 

 inferior to the others in this respect. 



The planes P, on a few of the crystals, exhibit delicate lines of 

 cleavage in two directions, approaching, but not identical with, 

 their edges of intersection with M and M ; which cleavage marks 

 are likewise visible on the lateral planes, both primary and sec- 

 ondary, as denoted in figure 2. The cleavage which takes place 

 in conformity with these lines, does not afford a solid of the 

 same dimensions with the primary form. Indeed, there is a con- 

 stant difference between the two cleavages, as to the facility 

 with which they are effected, and the lustre of the resulting 

 faces. The inclination of the most brilliant cleavage plane to P, 

 is between 130° and 131°, while the cleavage prism itself affords 



