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 
ina 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. 
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 al 
appearance. | Fig. 3 represents one of the. 
occurrence with the bevelment of the , the it 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 strize, 
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 strie on some of the 
crystals parallel with the opposite cleavage, appearing very rarely 
upon the acuminating faces. The larger crystals, which are 
