﻿444 
  

  

  Pratt 
  and 
  Foote 
  — 
  Wellsite. 
  a 
  new 
  Mineral. 
  

  

  is 
  wanting 
  and 
  a, 
  100 
  is 
  in 
  combination 
  with 
  b, 
  010. 
  The 
  

   method 
  of 
  twinning 
  is 
  similar 
  to 
  that 
  already 
  described, 
  but 
  

   the 
  crystals 
  being 
  terminated 
  by 
  a, 
  100 
  instead 
  of 
  m, 
  110 
  

   show 
  prominent 
  reentrant 
  angles 
  at 
  their 
  ends. 
  These 
  crystals 
  

   are 
  very 
  similar 
  to 
  those 
  of 
  harmotome 
  from 
  Bowling 
  near 
  

   Dumbarton 
  on 
  the 
  Clyde, 
  described 
  by 
  Lacroix.* 
  

  

  The 
  only 
  forms 
  that 
  were 
  observed 
  were 
  a, 
  100 
  ; 
  b, 
  010 
  ; 
  e, 
  

   001 
  and 
  m, 
  110, 
  with 
  e, 
  011 
  only 
  as 
  twinning 
  plane. 
  

  

  The 
  faces 
  of 
  the 
  crystals 
  are 
  somewhat 
  rounded 
  and 
  vicinal 
  

   so 
  that 
  the 
  reflections 
  were 
  not 
  very 
  perfect. 
  The 
  angle 
  of 
  

   the 
  apparent 
  prism 
  b^b 
  twinned 
  is 
  approximately 
  90°. 
  Also 
  

   the 
  angle 
  m^m 
  over 
  the 
  twinning 
  plane 
  011 
  could 
  be 
  measured 
  

   only 
  approximately, 
  varying 
  from 
  0° 
  49' 
  to 
  1° 
  25'. 
  The 
  

   approximate 
  angles 
  are 
  given 
  below, 
  and 
  from 
  those 
  marked 
  

   with 
  an 
  asterisk 
  the 
  following 
  axial 
  ratio 
  was 
  calculated 
  : 
  

  

  d:b:c='768 
  : 
  1 
  : 
  1-245; 
  /3= 
  53° 
  27' 
  = 
  001 
  a 
  100 
  

  

  bhb, 
  OIOaOJLO 
  

  

  aAffl, 
  100a 
  100 
  

   bhm, 
  010 
  AllO 
  

  

  CAfl, 
  001 
  A 
  100 
  

   CAM, 
  001 
  AllO 
  

  

  Measured. 
  

  

  *90° 
  (over 
  twinning 
  plane) 
  

   *73 
  6' 
  (over 
  twinning 
  plane) 
  

  

  *58 
  19 
  

   53 
  27 
  = 
  (3 
  

   60°, 
  59° 
  45', 
  59° 
  57' 
  

  

  Calculated. 
  

  

  59° 
  33' 
  

  

  Physical 
  properties. 
  — 
  The 
  crystals 
  are 
  brittle 
  and 
  show 
  no 
  

   apparent 
  cleavage. 
  The 
  luster 
  is 
  vitreous. 
  Many 
  of 
  the 
  crys- 
  

   tals 
  are 
  colorless 
  and 
  transparent 
  while 
  others 
  are 
  white. 
  The 
  

   hardness 
  is 
  between 
  4 
  and 
  4*5. 
  The 
  specific 
  gravity 
  taken 
  on 
  

   a 
  number 
  of 
  separate 
  crystals, 
  by 
  means 
  of 
  the 
  heavy 
  solution, 
  

   varied 
  between 
  2*278 
  and 
  2*366. 
  This 
  variation 
  was 
  probably 
  

  

  * 
  Bull, 
  de 
  la 
  Soc. 
  Mm. 
  de 
  France, 
  No. 
  4, 
  p. 
  94, 
  1885. 
  

  

  