﻿364 
  

  

  A. 
  F. 
  Rogers 
  — 
  Miner 
  alogical 
  Notes. 
  

  

  Aet. 
  XXXV. 
  — 
  Mineralogical 
  Notes; 
  by 
  Austin 
  F. 
  Bogers.* 
  

  

  1. 
  Gypsum. 
  — 
  The 
  gypsum 
  crystals 
  described 
  in 
  this 
  paper 
  

   were 
  obtained 
  by 
  the 
  writer 
  at 
  Lebo, 
  Coffey 
  Co., 
  Kansas. 
  

   They 
  occur 
  as 
  isolated 
  crystals 
  and 
  groups 
  in 
  Coal 
  Measure 
  

   shales 
  at 
  a 
  " 
  strip-pit" 
  coal 
  mine 
  located 
  at 
  the 
  edge 
  of 
  town. 
  

  

  Both 
  simple 
  and 
  twinned 
  crystals 
  were 
  found, 
  but 
  the 
  latter 
  

   are 
  of 
  especial 
  interest 
  because 
  they 
  appear 
  to 
  possess 
  hemi- 
  

   morphic-orthorhombic 
  symmetry 
  rather 
  than 
  monoclinic. 
  In 
  

   this 
  respect 
  they 
  resemble 
  gypsum 
  crystals 
  described 
  by 
  

   Pirssonf 
  from 
  Girgenti 
  in 
  Sicily. 
  Fig. 
  1, 
  an 
  orthographic 
  

  

  

  

  — 
  ^fc 
  

  

  10 
  

  

  

  Xj 
  

  

  

  

  

  \*a\ 
  

  

  Yn, 
  

  

  I 
  

  

  I 
  

  

  m 
  

  

  

  

  x\ 
  

  

  Si/ 
  

  

  

  »t 
  

  

  projection 
  of 
  one 
  of 
  the 
  twins 
  with 
  the 
  clinopinacoid 
  (010) 
  as 
  

   the 
  plane 
  of 
  projection 
  bears 
  a 
  striking 
  resemblance 
  to 
  Pirsson's 
  

   figure, 
  though 
  some 
  of 
  the 
  forms 
  are 
  different. 
  The 
  twinning 
  

   plane 
  and 
  composition 
  face 
  is 
  the 
  ordinary 
  one 
  for 
  gypsum, 
  

   a 
  (100) 
  i-i> 
  The 
  following 
  forms 
  were 
  observed 
  : 
  

  

  m(110)I; 
  b 
  (010) 
  i-l; 
  /(lll)-l; 
  x 
  (203)|-2; 
  u 
  (133) 
  1-3 
  

  

  The 
  form 
  %(203) 
  is 
  given 
  by 
  Goldschmidt 
  in 
  his 
  " 
  Index 
  der 
  

   Krystallformen 
  der 
  Mineralien 
  " 
  in 
  the 
  list 
  of 
  uncertain 
  forms. 
  

   As 
  the 
  faces 
  are 
  rather 
  dull 
  a 
  contact 
  goniometer 
  was 
  used 
  for 
  

   the 
  identification 
  of 
  the 
  forms. 
  The 
  results 
  are 
  as 
  follows 
  : 
  

  

  Average. 
  Calculated. 
  

   26° 
  28' 
  27° 
  00' 
  

  

  Limits. 
  

   X/sx(203^203) 
  10 
  measurements 
  26°-2'7 
  

  

  w^w(133/vl33) 
  10 
  measurements 
  43° 
  20'-45° 
  30' 
  44° 
  25' 
  44° 
  48' 
  

  

  Some 
  of 
  the 
  simple 
  crystals 
  are 
  very 
  flat 
  by 
  extension 
  of 
  

   Z 
  (111) 
  — 
  1. 
  Fig. 
  2 
  represents 
  a 
  cruciform 
  penetration 
  -twin 
  

   with 
  the 
  orthopinacoid 
  (100) 
  as 
  twinning 
  plane. 
  Fig. 
  3 
  may 
  

   be 
  considered 
  as 
  the 
  same 
  with 
  one 
  part 
  of 
  the 
  reversed 
  crys- 
  

  

  * 
  Published 
  by 
  permission 
  of 
  the 
  Director 
  of 
  the 
  University 
  Geological 
  Survey 
  

   of 
  Kansas. 
  

  

  f 
  L. 
  V. 
  Pirsson, 
  this 
  Journal, 
  vol. 
  xlii, 
  pp. 
  407, 
  408, 
  1891. 
  

  

  