Some  peculiar  conditions  attending  the  growth  of  the
crystal,  or  perhaps  some  force  which   has  acted  upon  it
since  it  was  formed,  has  resulted  in  bending  or  twisting  it
108.  out  of  its  normal  shape,  so  that  it  may

differ  widely  in  angle  from  the  regular
form.  Thus  the  faces  may  be  curved,  as
with  the  barrel-shaped  crystals  of  pyro-
morphite,  or  like  the  peculiar  convex  faces
common  on  crystals  of  the  diamond;  or  the  whole  crystal
may  be  bent,  as  is  seen  sometimes  in  the  case  of  crystals  of
quartz,  or  of  stibnite,  or  of  some  kinds  of  chlorite  (Fig.
108).
Or  again,  aside  from  this  curving  and  twisting,  a  crystal
may  have  had  its  shape  more  or  less  changed  by  some  force
exerted  in  the  rock  since  it  was  made;  it
may  even  have  been  broken  and  again
cemented  together,  so  that  many  irregu-
larities may  result.  Fig.  109  shows  a
crystal  of  beryl  which  has  been  broken
into  many  pieces,  these  slightly  displaced
from  each  other,  and  the  whole  cemented
together  by  quartz.
