Chap. III. ] 
BRAUNITE. 
59 
re-entrant angle, seem to be in a perfectly straight line ; whilst the two 
adjacent faces ABO and BCO are almost in the same plane, so that they 
seem to reflect light almost simultaneously, and, as viewed on the 
goniometer, give images that are only a few minutes distant from each 
other. Consequently, when the pyramid is not truncated by the basal 
plane in the way shown in fig. 6, the fact that the crystal is a twin is 
very apt to be overlooked. If, however, the crystal is cleaned its 
twinned nature is revealed by the existence on the apparently 
continuous plane AOC of the line BO. When the basal plane 
is present, the twinned character of the crystal is rendered obvious by 
the juxtaposition of the two planes c and c . These contact twins 
also show the faces y modifying p. In addition to the contact twins, 
inter penetration twins are common. One of these, composed of c, p, 
and X, is shown in fig. 7, the presence of x giving rise to re-entrant angles. 
Interpenetration twins of the form c, p, and ^J, have also been found, 
as in fig. 8. 
One other habit that requires notice is that illustrated in 
fig. 9, in which the forms represented are v, x, ti, and 
A new i 01111. . r.,, , ■ s. ^ . , 
the new face ij. The latter is, of course, a pyramid 
of the second order, steeper than the pyramid of the second order, e or 
(101), mentioned above as a twinning plane, but to be noticed below as a 
Fig. 9. — Braunite, Kacharwahi. Fig. 10. — Braunite, Lohdongri. 
face actually observed. The specimen from which this figure was drawn 
was a minute chip showing only one corner of the crystal with two p 
