TN 
Crystallographic Examination of Eremite. 71 
twentieth of an inch. The smaller crystals seldom present brilliant 
faces, and for this reason, as also on account of their minuteness, 
they scarcely admit of the use of the reflective goniometer. The 
larger crystal, on the contrary, possesses highly polished surfaces, 
admitting of easy and accurate measurement. ‘The data for the fol- 
lowing calculations have therefore been obtained from the latter alone. 
Owing to the completeness of the different series of parallel inter- 
sections, the crystallographic expressions for the planes of eacl 
the crystals may be deduced with perfect facility and certainty, inde- 
pendently of measurement ; and hence, although the planes in some 
instances are microscopic, their interfacial angles may be accurately 
determined by calculation. The following are representations of 
three of these crystals. 
Fig. 2, a. 
The character of the crystals is obviously monoclinate. There 
are no traces of cleavage to indicate whether the primary is the ob- 
lique rhombic or right rhomboidal prism ; but the sizevand brilliancy 
of M and P, two faces of the rhomboidal prism, and the occasional 
absence of the planes e, e’ which belong to rhombic prisms, favor the 
conclusion that the latter is the primary. The third plane T, of the 
rhomboidal prism, has been obliterated by the extension of € and €.* 
The crystals have been lettered in accordance with this view; the 
+ The figures represent the crystals as standing on one of their rectangular 
primary faces (T) asa base. The obtuse edge between M and T, is replaced by 
the plane é, and the acute edge by é. 
