﻿No, 
  30.] 
  

  

  83 
  

  

  Figs. 
  Ij 
  2^ 
  3, 
  represent 
  modifications 
  of 
  the 
  pyramid 
  of 
  the 
  

   scalene 
  dodecahedron, 
  in 
  which 
  the 
  summit 
  is 
  replaced 
  by 
  a 
  

   single 
  hexagonal 
  plane, 
  perpendicular 
  to 
  the 
  axis 
  of 
  the 
  crystal. 
  

   In 
  fig. 
  2, 
  every 
  alternate 
  solid 
  angle 
  at 
  the 
  summit, 
  is 
  replaced 
  

   by 
  a 
  plane 
  with 
  cleavage 
  parallel 
  to 
  its 
  surface, 
  and 
  therefore 
  a 
  

   part 
  of 
  the 
  primary 
  rhombahedron. 
  In 
  fig. 
  3, 
  these 
  planes 
  are 
  

   enlarged 
  so 
  as 
  to 
  reduce 
  the 
  terminal 
  plane 
  to 
  a 
  triangle, 
  and 
  in 
  

   fig. 
  4, 
  this 
  plane 
  is 
  entirely 
  destroyed, 
  and 
  the 
  crystal 
  presents 
  

   the 
  usual 
  form 
  of 
  the 
  binaire, 
  of 
  Ha'iiy, 
  or 
  a 
  scalene 
  dodecahedron 
  

   with 
  a 
  summit 
  of 
  three 
  rhomboidal 
  faces. 
  The 
  measurement 
  of 
  

   these 
  planes 
  are 
  calculated 
  as 
  follows: 
  0. 
  on 
  R., 
  113° 
  17' 
  ; 
  on 
  

   P., 
  142° 
  14' 
  ; 
  as 
  derived 
  from 
  the 
  measure 
  of 
  the 
  angles 
  P. 
  on 
  R-, 
  

   and 
  R. 
  on 
  R., 
  as 
  given 
  in 
  the 
  State 
  report 
  on 
  mineralogy, 
  page 
  

   219. 
  All 
  of 
  these 
  forms 
  occur 
  in 
  the 
  specimens 
  transmitted 
  to 
  

   the 
  State 
  collection. 
  It 
  is 
  very 
  probable 
  that 
  actual 
  measurement 
  

   might 
  give 
  diiferent 
  angles 
  from 
  those 
  calculated 
  above. 
  

  

  Fig:. 
  5, 
  

  

  Fig. 
  6. 
  

  

  Fi-. 
  7, 
  

  

  Figs. 
  5, 
  6,7, 
  represent 
  modifications 
  observed 
  in 
  the 
  pyramid, 
  

   by 
  the 
  extension 
  of 
  some 
  of 
  the 
  planes, 
  and 
  the 
  extinction 
  of 
  

   others. 
  

  

  Fig. 
  8, 
  represents 
  a 
  common 
  form 
  at 
  the 
  locality. 
  The 
  

   reentrant 
  planes 
  indicate 
  its 
  compound 
  character. 
  When 
  but 
  

   partly 
  developed, 
  it 
  presents 
  in 
  certain 
  positions 
  the 
  appearance 
  

   of 
  a 
  low 
  four 
  sided 
  pyramid 
  . 
  In 
  some 
  instances 
  the 
  pyramid 
  is 
  

   modified 
  by 
  six 
  additional 
  planes 
  which 
  make 
  the 
  summit 
  a 
  

   little 
  more 
  obtuse, 
  as 
  is 
  represented 
  in 
  fig. 
  9. 
  

  

  