Notice of Minerals from New Holland. 



159 



terminal primary faces P, at both extremities of the crystals ; thus 

 tending to two four-sided pyramids having square bases, as in 

 Fig. 1. But as the crystals are usually implanted on the matrix 

 in a vertical position, they commonly present only one of the pyra- 

 mids, the apex being entire, or showing a portion (sometimes only 

 visible by the microscope) of the summits of the prism, as in 

 Fig. 2. Sometimes one of the faces of the pyramids is conside- 

 rably extended at the expense of the two adjoining ones. 



Fig. 1. 



Fig. 3. 



The lateral edges from a to a, Fig. 1, are always replaced, some- 

 times by a tangent plane, inclining equally upon the two adja- 

 cent lateral planes, but most frequently by two planes, each of 

 these being again followed by another very narrow plane, leaving 

 scarcely any remaining portion of the primary faces; thus impart- 

 ing to the crystals an oval or cylindrical shape, and, in connexion 

 with the low pyramids of the summits, rather a barrel-shaped 

 appearance. Fig. 3 represents one of the crystals of occasional 

 occurrence with the bevelment of the edges, the decrement of 

 the summit being complete and showing the whole of the low- 

 er pyramid, where it unites with the matrix. Fig. 4 represents 

 another of these crystals with the additional planes. The dotted 

 lines on these figures are intended to show deep grooves, or striae, 

 which extend longitudinally along the faces of the crystals, or 

 parallel with their prismatic axes, and probably indicate the faces 

 of cleavage in this direction. This cleavage, however, is ob- 

 tained with great difficulty, as is the case with this mineral from 

 other localities. There are also transverse strias on some of the 

 crystals parallel with the opposite cleavage, appearing very rarely 

 upon the acuminating faces. The larger crystals, which are 



