﻿118 
  JY. 
  L. 
  Bowen 
  — 
  Sodium- 
  Potassium 
  Nejphelites. 
  

  

  divided 
  into 
  six 
  sextants 
  that 
  extinguish 
  together 
  in 
  opposite 
  

   pairs. 
  Occasionally 
  polysynthetic 
  twinning 
  similar 
  to 
  that 
  in 
  

   albite 
  is 
  shown, 
  but 
  this 
  appears 
  to 
  follow 
  the 
  same 
  law 
  as 
  the 
  

   previous 
  case 
  with 
  the 
  same 
  prism 
  face 
  acting 
  repeatedly 
  as 
  

   composition 
  face 
  instead 
  of 
  adjacent 
  faces 
  as 
  in 
  the 
  case 
  of 
  

   penetration 
  twins. 
  

  

  Crystals 
  of 
  this 
  orthorhombic 
  form 
  were 
  made 
  by 
  fusing 
  

   together 
  silica, 
  alumina 
  and 
  potassium 
  fluoride 
  over 
  a 
  Bunsen 
  

   burner 
  after 
  the 
  method 
  of 
  Duboine.* 
  The 
  twinning 
  was 
  not 
  

   so 
  frequently 
  developed 
  as 
  in 
  the 
  crystals 
  obtained 
  at 
  high 
  

   temperatures 
  but 
  occasionally 
  appeared 
  in 
  typical 
  form. 
  The 
  

   refractive 
  indices 
  are 
  7 
  = 
  1-536, 
  a 
  = 
  1*528, 
  2Y 
  = 
  39 
  ± 
  3° 
  

   negative. 
  

  

  The 
  product 
  obtained 
  by 
  this 
  method 
  is 
  not 
  strictly 
  pure 
  but 
  

   contains 
  an 
  amount 
  of 
  foreign 
  material 
  estimated 
  under 
  the 
  

   microscope 
  to 
  be 
  about 
  5 
  per 
  cent. 
  This 
  consists 
  of 
  isotropic 
  

   octahedra 
  whose 
  refractive 
  index 
  is 
  about 
  1'510. 
  The 
  corre- 
  

   spondence 
  with 
  the 
  compound 
  K 
  2 
  Al 
  2 
  SiO 
  G 
  as 
  described 
  by 
  Wey- 
  

   bergf 
  is 
  complete. 
  

  

  Analysis 
  of 
  this 
  mixture 
  resulted 
  as 
  follows 
  : 
  

  

  Si0 
  2 
  36-7 
  38-07 
  

  

  Al 
  a 
  3 
  32-8 
  32-21 
  

  

  KO' 
  30-3 
  29-72 
  

  

  99-8 
  100-00 
  

  

  I 
  Product 
  obtained 
  from 
  fusion 
  with 
  KF. 
  Analyst 
  N". 
  L. 
  

   Bowen. 
  

   II 
  KAlSi0 
  4 
  , 
  theoretical 
  composition. 
  

  

  It 
  w 
  T 
  ill 
  be 
  noted 
  that 
  the 
  analyzed 
  material 
  is 
  low 
  in 
  silica 
  

   and 
  high 
  in 
  alumina 
  and 
  potash 
  and 
  calculation 
  shows 
  that 
  it 
  

   corresponds 
  with 
  a 
  mixture 
  of 
  93 
  per 
  cent 
  KAlSi0 
  4 
  with 
  7 
  per 
  

   cent 
  K 
  2 
  Al 
  2 
  Si0 
  6 
  . 
  The 
  analysis 
  and 
  the 
  microscopic 
  examination 
  

   together 
  may 
  therefore 
  be 
  regarded 
  as 
  definitely 
  proving 
  that 
  

   the 
  foreign 
  material 
  is 
  K 
  2 
  Al 
  2 
  Si0 
  6 
  present 
  to 
  the 
  extent 
  of 
  

   about 
  5-7 
  per 
  cent 
  and 
  that 
  the 
  twinned 
  material 
  corresponds 
  

   with 
  kaliophilite 
  in 
  composition. 
  

  

  Glass 
  of 
  composition 
  KAlSi0 
  4 
  (approximately) 
  has 
  a 
  refrac- 
  

   tive 
  index 
  for 
  sodium 
  light 
  of 
  1*508 
  zb 
  *002. 
  

  

  A 
  number 
  of 
  supposed 
  other 
  forms 
  of 
  KAlSi0 
  4 
  have 
  been 
  

   encountered 
  by 
  various 
  investigators, 
  but 
  the 
  material 
  was 
  

   always 
  poorly 
  crystallized 
  and 
  the 
  measured 
  properties 
  were 
  

   hardly 
  sufficient 
  to 
  individualize 
  them 
  as 
  species. 
  No 
  crystal- 
  

   line 
  forms 
  of 
  KAlSiO. 
  other 
  than 
  the 
  two 
  described 
  were 
  

   encountered 
  during 
  the 
  course 
  of 
  the 
  present 
  work. 
  The 
  

  

  *Bull. 
  Soc. 
  Mhi. 
  Fr., 
  xv, 
  191, 
  1892. 
  

  

  f 
  " 
  In 
  Canada-balsam 
  sehr 
  schwer 
  sichtbar," 
  Weyberg, 
  Centralblatt 
  Min. 
  

   1908, 
  p. 
  329. 
  

  

  