﻿226 
  A. 
  P. 
  lioness 
  — 
  Etching 
  Figures 
  of 
  Beryl. 
  

  

  amined 
  under 
  the 
  microscope. 
  No 
  attempt 
  was 
  made 
  to 
  etch 
  

   the 
  unit 
  first-order 
  pyramid 
  with 
  sodium 
  hydroxide, 
  as 
  its 
  sur- 
  

   face 
  was 
  rather 
  irregular, 
  but 
  undoubtedly 
  the 
  form 
  would 
  

   yield 
  distinct 
  figures 
  if 
  a 
  more 
  perfect 
  surface 
  could 
  be 
  obtained. 
  

   In 
  general, 
  then, 
  the 
  figures 
  produced 
  by 
  sodium 
  hydroxide 
  are 
  

   very 
  distinct 
  and 
  easily 
  and 
  quickly 
  produced, 
  and 
  are 
  perhaps 
  

   more 
  simple 
  in 
  form 
  than 
  those 
  produced 
  bj 
  the 
  potassium 
  

   hydroxide 
  fusion 
  next 
  to 
  be 
  considered. 
  

  

  .Etching 
  with 
  Potassium 
  hydroxide. 
  

  

  After 
  immersion 
  in 
  the 
  fused 
  potassium 
  hydroxide 
  for 
  fifteen 
  

   seconds, 
  the 
  unit 
  prism 
  1010 
  was 
  densely 
  pitted 
  with 
  etchings 
  

   of 
  sufficient 
  size 
  as 
  to 
  permit 
  detailed 
  study. 
  The 
  base, 
  

   0001, 
  was 
  also 
  perfectly 
  etched 
  with 
  a 
  countless 
  number 
  of 
  

   circular 
  pits, 
  so 
  small 
  that 
  they 
  revealed 
  no 
  angles 
  under 
  high 
  

   magnification. 
  The 
  first 
  and 
  second-order 
  pyramids 
  were 
  not 
  

   etched 
  as 
  yet, 
  but 
  repeated 
  immersions 
  for 
  two 
  or 
  three 
  minutes 
  

   gradually 
  developed 
  distinct 
  forms 
  on 
  the 
  first-order 
  pyramid, 
  

   but 
  those 
  of 
  the 
  second 
  remained 
  imperfect 
  and 
  dim. 
  

  

  Prism. 
  — 
  The 
  prism 
  figures, 
  like 
  those 
  of 
  the 
  sodium 
  

   hydroxide, 
  are 
  of 
  two 
  kinds, 
  and 
  in 
  general 
  resemble 
  them. 
  

   There 
  is 
  noticed, 
  however, 
  under 
  high 
  magnification, 
  a 
  distinct 
  

   difference 
  in 
  the 
  etch 
  figures 
  of 
  the 
  two 
  solvents 
  ; 
  those 
  pro- 
  

   duced 
  by 
  sodium 
  hydroxide 
  are 
  simple 
  in 
  form, 
  while 
  those 
  

   produced 
  by 
  the 
  potassium 
  hydroxide 
  fusion 
  are 
  complex. 
  The 
  

   more 
  simple 
  type 
  of 
  potassium 
  hydroxide 
  figures 
  (6, 
  fig. 
  5) 
  are 
  

   very 
  shallow 
  and 
  bounded 
  by 
  three 
  planes, 
  the 
  largest 
  of 
  which 
  

   is 
  curved, 
  forming 
  the 
  base 
  and 
  ends 
  of 
  the 
  pits. 
  The 
  lateral 
  

   bounding 
  faces, 
  slightly 
  bulged, 
  descend 
  very 
  abruptly 
  to 
  meet 
  

   the 
  base, 
  forming 
  a 
  simple 
  quadrilateral 
  figure, 
  with 
  the 
  

   extremities 
  slightly 
  rounded. 
  The 
  forms 
  are 
  elongated 
  parallel 
  

   to 
  the 
  c-axis 
  of 
  the 
  crystal 
  and 
  are 
  symmetrical 
  to 
  two 
  planes. 
  

   The 
  more 
  complex 
  etch 
  figures 
  are 
  apparently 
  made 
  up 
  of 
  two 
  

   pairs 
  of 
  lateral 
  faces 
  (c/, 
  fig. 
  5). 
  The 
  first 
  pair, 
  which 
  gives 
  the 
  

   figure 
  its 
  general 
  form, 
  is 
  much 
  curved, 
  and 
  descends 
  quite 
  

   abruptly 
  to 
  the 
  edge 
  of 
  a 
  deep 
  pit, 
  produced 
  by 
  the 
  second 
  pair 
  

   of 
  lateral 
  faces, 
  which 
  seem 
  to 
  meet 
  the 
  base 
  of 
  the 
  figure 
  

   almost 
  perpendicularly. 
  The 
  deeper 
  part 
  of 
  the 
  pit 
  is 
  bounded 
  

   by 
  faces 
  extending 
  parallel 
  to 
  the 
  long 
  axis 
  of 
  the 
  figure 
  ; 
  the 
  

   ends 
  are 
  modified 
  by 
  two 
  faces 
  meeting 
  in 
  a 
  point 
  at 
  a 
  very 
  

   sharp 
  angle, 
  and 
  these, 
  like 
  the 
  lateral 
  faces, 
  extend 
  upward 
  to 
  

   meet 
  the 
  more 
  gently 
  sloping 
  planes, 
  which 
  give 
  the 
  figure 
  its 
  

   shape 
  and 
  which, 
  in 
  reality, 
  are 
  the 
  uppermost 
  lateral 
  planes 
  

   partly 
  enveloping 
  the 
  ends 
  of 
  the 
  pit. 
  It 
  is 
  not 
  an 
  uncommon 
  

   thing 
  to 
  observe 
  on 
  a 
  single 
  prism 
  face, 
  figures 
  which 
  are 
  

   representative 
  of 
  four 
  different 
  stages 
  of 
  development, 
  or 
  a 
  

   change 
  from 
  the 
  simplest 
  to 
  the 
  most 
  complex, 
  as 
  is 
  indicated 
  

  

  