﻿136 
  Rogers 
  — 
  Sphalerite 
  Crystals 
  of 
  a 
  Peculiar 
  Habit. 
  

  

  axis 
  of 
  symmetry 
  bd 
  parallel 
  to 
  the 
  shorter 
  diagonal 
  of 
  the 
  

   faces 
  of 
  the 
  dodecahedron. 
  Approximate 
  measurements 
  of 
  

   the 
  angles 
  aba 
  and 
  ado 
  gave 
  110° 
  and 
  80° 
  respectively. 
  The 
  

   solid 
  angle 
  at 
  b 
  is 
  elevated 
  above 
  the 
  general 
  surface 
  of 
  the 
  

   crystal, 
  while 
  the 
  points 
  <2, 
  c, 
  and 
  d 
  are 
  on 
  this 
  surface. 
  In 
  

   elevation, 
  therefore, 
  the 
  etch-hills 
  appear 
  as 
  in 
  fig. 
  4. 
  Here 
  

  

  the 
  angle 
  ebd 
  is 
  near 
  90°. 
  The 
  edges 
  ab 
  and 
  bo 
  and 
  the 
  solid 
  

   angle 
  at 
  b 
  are 
  modified 
  by 
  minute 
  faces 
  which 
  are 
  hot 
  repre- 
  

   sented 
  in 
  the 
  drawing. 
  The 
  " 
  figure 
  faces 
  ? 
  '* 
  abd 
  and 
  bed 
  are 
  

   highly 
  polished 
  and 
  seem 
  to 
  reflect 
  light 
  at 
  the 
  same 
  angle 
  

   that 
  the 
  g 
  faces 
  do, 
  so 
  that 
  these 
  figure-faces 
  may 
  perhaps 
  be 
  

   represented 
  by 
  the 
  same 
  symbol. 
  The 
  etch-figures 
  resemble 
  

   those 
  described 
  by 
  Beckef 
  except 
  that 
  the 
  lines 
  corresponding 
  

   to 
  ab 
  and 
  bo 
  in 
  fig. 
  3 
  are 
  parallel 
  to 
  the 
  edges 
  of 
  the 
  dodeca- 
  

   hedron 
  while 
  the 
  lines 
  in 
  our 
  figure 
  are 
  inclined 
  about 
  20° 
  

   thereto. 
  In 
  Becke's 
  illustration 
  the 
  acute 
  angle 
  of 
  the 
  mono- 
  

   symmetric 
  etch-figures 
  points 
  toward 
  the 
  negative 
  octant. 
  As 
  

   this 
  acute 
  angle 
  on 
  our 
  crystals 
  points 
  away 
  from 
  the 
  <r 
  faces,, 
  

   the 
  latter 
  are 
  the 
  faces 
  of 
  the 
  positive 
  hemi-tetragonal 
  trisocta- 
  

   hedron 
  or 
  (833), 
  J-f_and 
  the 
  prominent 
  dodecahedral 
  faces 
  are 
  

   (101), 
  (110), 
  and 
  (011). 
  

  

  In 
  conclusion 
  I 
  wish 
  to 
  thank 
  Prof. 
  E. 
  Haworth 
  for 
  sugges- 
  

   tions 
  in 
  the 
  preparation 
  of 
  this 
  paper. 
  

  

  Mineralogical 
  Laboratory, 
  University 
  of 
  Kansas, 
  

  

  Lawrence, 
  Kansas, 
  December, 
  1899. 
  

  

  * 
  Daly, 
  loc. 
  cit. 
  

  

  fBecke, 
  loc. 
  cit. 
  Figure 
  copied 
  by 
  Tschermak, 
  Lehrbuch 
  der 
  Mineralogie 
  f 
  

   p. 
  145. 
  

  

  