﻿406 
  L. 
  V. 
  Pirsson 
  — 
  Miner 
  alogical 
  Notes. 
  

  

  resemble 
  the 
  example 
  of 
  this 
  method 
  of 
  twinning 
  given 
  by 
  

   Kokscharow* 
  in 
  the 
  development 
  of 
  the 
  brachydomes. 
  The 
  

   figure 
  shows 
  them 
  in 
  ideal 
  symmetry; 
  they 
  are 
  generally 
  at- 
  

   tached 
  by 
  the 
  barb-shaped 
  end 
  ; 
  sometimes 
  one 
  barb 
  or 
  indi- 
  

   vidual 
  is 
  free 
  with 
  the 
  faces 
  developed 
  as 
  in 
  the 
  figure 
  ; 
  in 
  other 
  

   forms 
  both 
  individuals 
  are 
  attached 
  and 
  the 
  barb-like 
  part 
  is 
  

   wanting. 
  They 
  occur 
  on 
  the 
  specimen 
  seen, 
  with 
  cerargyrite 
  

   and 
  wulfenite. 
  The 
  forms 
  observed 
  on 
  these 
  crystals 
  are 
  : 
  

  

  r, 
  i-3, 
  130; 
  Jc, 
  1-z, 
  Oil; 
  v, 
  3-t, 
  031; 
  x, 
  \-% 
  012; 
  to, 
  I, 
  110; 
  p. 
  1, 
  111. 
  

  

  Also 
  the 
  pinacoids 
  i-i, 
  100 
  and 
  %-% 
  010, 
  the 
  pyramid 
  J, 
  112 
  

  

  and 
  the 
  brachy-diagonal 
  pyramid 
  2-2, 
  121 
  have 
  been 
  identified 
  

   in 
  zones 
  on 
  the 
  reflecting 
  goniometer 
  and 
  measured 
  with 
  some 
  

   accuracy, 
  but 
  they 
  are 
  too 
  minutely 
  developed 
  to 
  give 
  any 
  

   character 
  to 
  the 
  crystals 
  and 
  are 
  hence 
  omitted 
  in 
  the 
  figures. 
  

   The 
  crystals 
  are 
  well 
  suited 
  for 
  measurement, 
  the 
  faces 
  gener- 
  

   ally 
  giving 
  good 
  reflections 
  of 
  the 
  signal. 
  

  

  Fig. 
  2 
  shows 
  a 
  crystal 
  from 
  the 
  same 
  place 
  with 
  a 
  different 
  

   habit, 
  the 
  large 
  -J- 
  brachydoine 
  x 
  and 
  great 
  development 
  of 
  the 
  

   brachy-prism 
  r 
  having 
  resulted 
  in 
  a 
  long 
  spindle-shape 
  form. 
  

   Fig. 
  3 
  shows 
  the 
  same 
  individual 
  in 
  basal 
  projection. 
  It 
  oc- 
  

   curred, 
  attached 
  at 
  the 
  end 
  with 
  the 
  re-entrant 
  angle, 
  which 
  in 
  

   consequence 
  was 
  somewhat 
  broken. 
  Otherwise 
  the 
  crystal 
  is 
  

   quite 
  perfect 
  and 
  in 
  size 
  about 
  an 
  inch 
  long. 
  The 
  zone 
  of 
  

   brachydomes 
  is 
  somewhat 
  striated, 
  causing 
  a 
  rounding 
  off 
  

   toward 
  the 
  point. 
  The 
  signals 
  of 
  the 
  prominent 
  faces 
  are, 
  

   however, 
  very 
  distinct 
  and 
  give 
  good 
  measurements. 
  On 
  this 
  

   crystal 
  the 
  forms 
  observed 
  were 
  : 
  

  

  b, 
  i-% 
  010; 
  c, 
  O, 
  001; 
  r, 
  i-3, 
  130; 
  k, 
  l-i, 
  011; 
  x, 
  H, 
  012. 
  

  

  The 
  following 
  table 
  shows 
  the 
  identification 
  of 
  the 
  forms 
  by 
  

   calculated 
  and 
  measured 
  (supplementary) 
  angles. 
  

  

  

  

  Calculated. 
  

  

  Measured. 
  

  

  k 
  *p 
  

  

  011 
  ^ 
  111 
  

  

  43° 
  

  

  50' 
  

  

  40" 
  

  

  43° 
  51' 
  

  

  m 
  s,p 
  

  

  no 
  ^ 
  in 
  

  

  35 
  

  

  46 
  

  

  20 
  

  

  35 
  45, 
  35 
  50, 
  35 
  49 
  

  

  k 
  *r 
  

  

  011a 
  130 
  

  

  59 
  

  

  03 
  

  

  10 
  

  

  59 
  00 
  

  

  P*P 
  

  

  111 
  A 
  111 
  

  

  49 
  

  

  59 
  

  

  30 
  

  

  49 
  58 
  

  

  m 
  ~r 
  

  

  110a 
  130 
  

  

  29 
  

  

  57 
  

  

  30 
  

  

  30 
  00, 
  30 
  01 
  

  

  p 
  a 
  r 
  

  

  111 
  a 
  130 
  

  

  45 
  

  

  19 
  

  

  55 
  

  

  45 
  16, 
  45 
  22 
  

  

  V 
  a 
  V 
  

  

  031 
  ~ 
  031 
  

  

  49 
  

  

  30 
  

  

  

  49 
  27 
  

  

  k 
  * 
  x 
  

  

  011a012 
  

  

  15 
  

  

  59 
  

  

  30 
  

  

  16 
  00, 
  16 
  04 
  

  

  k~k 
  

  

  OUaOII 
  

  

  108 
  

  

  16 
  

  

  

  108 
  12, 
  108 
  14 
  

  

  r 
  a 
  x 
  

  

  130 
  a 
  012 
  

  

  72 
  

  

  38 
  

  

  30 
  

  

  72 
  35 
  

  

  CaX 
  

  

  001 
  a 
  012 
  

  

  19 
  

  

  52 
  

  

  30 
  

  

  19 
  48 
  

  

  r~b 
  

  

  130 
  a 
  010 
  

  

  28 
  

  

  39 
  

  

  30 
  

  

  28 
  37, 
  28 
  31 
  

  

  k~b 
  

  

  011 
  a010 
  

  

  54 
  

  

  08 
  

  

  

  54 
  17 
  

  

  

  001 
  a 
  112 
  

  

  34 
  

  

  46 
  

  

  

  34 
  54 
  

  

  

  121 
  a 
  121 
  

  

  85 
  

  

  59 
  

  

  

  86 
  00 
  

  

  * 
  Min. 
  Russl., 
  vi, 
  pp. 
  106, 
  1870. 
  Also 
  Atlas 
  Taf. 
  lxxx, 
  figs. 
  20 
  and 
  20 
  bis. 
  

  

  