﻿126 
  JS 
  r 
  . 
  L. 
  Boiven 
  — 
  Sodium- 
  Potassium 
  JVephelites. 
  

  

  philite 
  with 
  its 
  parallel 
  extinction 
  is 
  broken 
  up 
  into 
  two 
  or 
  

   more 
  areas 
  which 
  are 
  in 
  twinned 
  relation 
  with 
  each 
  other 
  and 
  

   whose 
  extinction 
  has 
  no 
  relation 
  to 
  the 
  elongation. 
  At 
  about 
  

   1540°, 
  therefore, 
  or 
  possibly 
  somewhat 
  lower, 
  the 
  hexagonal 
  

   kaliophilite 
  is 
  converted 
  into 
  the 
  orthorhombic 
  form. 
  The 
  

   formation 
  of 
  the 
  orthorhombic 
  form 
  at 
  low 
  temperatures 
  with 
  

   fluxes 
  is 
  not 
  at 
  all 
  incompatible 
  with 
  its 
  stability 
  at 
  high 
  tem- 
  

  

  Fig. 
  2. 
  

  

  

  - 
  

  

  * 
  i 
  

  

  / 
  I 
  

  

  , 
  i 
  

  

  1700- 
  

  

  

  / 
  i 
  

  

  / 
  i 
  

  

  / 
  i 
  

  

  / 
  i 
  

  

  1600- 
  

  

  

  / 
  i 
  

   i 
  

   i 
  

  

  i 
  

  

  

  

  ' 
  "■ 
  — 
  •«. 
  s 
  

  

  / 
  — 
  - 
  .. 
  X 
  

  

  1500- 
  

  

  

  

  1400. 
  

   1300. 
  

  

  

  

  

  

  1200. 
  

  

  

  

  NaAlSiO. 
  

  

  10 
  

  

  20 
  

  

  30 
  

  

  40 
  50 
  

  

  WT 
  PER 
  CENT 
  

  

  60 
  

  

  70 
  

  

  80 
  

  

  90 
  

  

  KAlSO, 
  

  

  peratures 
  only, 
  for 
  many 
  such 
  forms 
  can 
  be 
  so 
  obtained, 
  notable 
  

   examples 
  being 
  the 
  forms 
  of 
  silica.* 
  The 
  writer 
  has 
  not, 
  how- 
  

   ever, 
  been 
  able 
  to 
  convert 
  the 
  orthorhombic 
  form 
  into 
  the 
  

   hexagonal 
  form, 
  but 
  this 
  does 
  not 
  necessarily 
  preclude 
  an 
  enan- 
  

   tiotropic 
  relation 
  between 
  them, 
  for 
  it 
  is 
  not 
  uncommon 
  to 
  

   experience 
  great 
  difficulty 
  in 
  converting 
  the 
  high 
  temperature 
  

   form 
  into 
  its 
  low 
  temperature 
  equivalent. 
  

  

  *C. 
  N. 
  Fenner, 
  this 
  Journal 
  (4), 
  xxxvi, 
  339, 
  1013. 
  

  

  