﻿N. 
  L. 
  Bowen 
  — 
  Sodium- 
  Potassium 
  N&phelites. 
  125 
  

  

  must 
  conclude 
  that 
  the 
  moderate 
  amount 
  of 
  KAlSi0 
  4 
  usually 
  

   found 
  entering 
  into 
  nephelite 
  is 
  the 
  result 
  of 
  a 
  deficiency 
  of 
  

   supply 
  rather 
  than 
  of 
  any 
  inability 
  on 
  the 
  part 
  of 
  nephelite 
  to 
  

   take 
  up 
  greater 
  quantities 
  in 
  solid 
  solution. 
  

  

  Crystallization 
  of 
  a 
  Typical 
  Mixture. 
  

  

  The 
  phenomena 
  observed 
  during 
  the 
  cooling 
  of 
  a 
  mixture 
  in 
  

   which 
  perfect 
  equilibrium 
  is 
  attained 
  are, 
  perhaps, 
  of 
  sufficient 
  

   interest 
  to 
  be 
  described 
  in 
  detail. 
  A 
  mixture 
  of 
  80 
  per 
  cent 
  

   NaAlSi0 
  4 
  and 
  20 
  per 
  cent 
  KAlSi0 
  4 
  begins 
  to 
  crystallize 
  at 
  

   1438° 
  with 
  separation 
  of 
  crystals 
  of 
  carnegieite 
  containing 
  6 
  

   per 
  cent 
  KAlSi0 
  4 
  (see 
  fig. 
  1). 
  As 
  the 
  temperature 
  falls 
  the 
  

   liquid 
  changes 
  in 
  composition 
  towards 
  the 
  eutectic 
  and 
  the 
  

   carnegieite 
  crystals 
  increase 
  in 
  amount 
  and 
  become 
  richer 
  in 
  

   potash 
  content. 
  At 
  the 
  eutectic 
  temperature, 
  1404°, 
  they 
  con- 
  

   tain 
  about 
  16 
  per 
  cent 
  KAlSi0 
  4 
  and 
  are 
  then 
  joined 
  by 
  hex- 
  

   agonal 
  crystals 
  (nephelite) 
  containing 
  35 
  per 
  cent 
  KAlSi0 
  4 
  . 
  

   The 
  temperature 
  remains 
  constant 
  until 
  all 
  the 
  liquid 
  has 
  dis- 
  

   appeared. 
  Then 
  as 
  the 
  temperature 
  falls 
  carnegieite 
  immedi- 
  

   ately 
  begins 
  to 
  invert 
  to 
  nephelite 
  and 
  both 
  change 
  in 
  composi- 
  

   tion, 
  becoming 
  richer 
  in 
  soda, 
  until 
  at 
  1348° 
  all 
  the 
  carnegieite 
  

   has 
  changed 
  to 
  nephelite 
  which 
  now 
  has 
  the 
  composition 
  

   ISTaAlSiO, 
  80 
  per 
  cent, 
  KAlSi0 
  4 
  20 
  per 
  cent. 
  

  

  Relation 
  between 
  the 
  hexagonal 
  aucl 
  orthorhombic 
  forms 
  of 
  

   KAlSiO 
  v 
  — 
  Both 
  forms 
  of 
  KAlSi0 
  4 
  can 
  be 
  obtained 
  at 
  low 
  

   temperatures. 
  Kaliophilite 
  has 
  been 
  obtained 
  hydrothermally 
  

   by 
  Storey 
  and 
  several 
  others 
  at 
  temperatures 
  in 
  the 
  neighbor- 
  

   hood 
  of 
  500°. 
  The 
  orthorhombic 
  form 
  was 
  prepared 
  in 
  a 
  simi- 
  

   lar 
  manner 
  by 
  Lemberg.* 
  Both 
  forms 
  can 
  likewise 
  be 
  obtained 
  

   with 
  the 
  aid 
  of 
  various 
  fluxes 
  at 
  moderate 
  temperatures. 
  

   Nevertheless 
  a 
  number 
  of 
  facts 
  point 
  to 
  the 
  stability 
  of 
  kalio- 
  

   philite 
  only 
  at 
  low 
  temperatures 
  and 
  of 
  the 
  orthorhombic 
  form 
  

   only 
  at 
  high 
  temperatures 
  with 
  the 
  inversion 
  temperature 
  

   somewhere 
  in 
  the 
  neighborhood 
  of 
  1540°. 
  In 
  the 
  present 
  

   mixtures 
  when 
  working 
  without 
  fluxes 
  the 
  orthorhombic 
  form 
  

   was 
  obtained 
  only 
  in 
  mixtures 
  containing 
  TO 
  per 
  cent 
  or 
  more 
  

   of 
  KAlSi0 
  4 
  and 
  in 
  these 
  only 
  at 
  high 
  temperatures. 
  More- 
  

   over, 
  ordinary 
  uniaxial 
  kaliophilite 
  formed 
  by 
  crystallizing 
  

   glass 
  made 
  in 
  the 
  iridium 
  furnace, 
  is 
  converted 
  at 
  1550° 
  into 
  

   excellent 
  twinned 
  crystals 
  of 
  the 
  orthorhombic 
  form. 
  The 
  

   change 
  is 
  here 
  facilitated 
  by 
  the 
  formation 
  of 
  a 
  little 
  liquid 
  as 
  

   a 
  result 
  of 
  the 
  deviation 
  of 
  the 
  material 
  from 
  the 
  true 
  composi- 
  

   tion. 
  Pure 
  kaliophilite 
  made 
  by 
  Morey 
  suffers 
  a 
  change 
  at 
  

   about 
  the 
  same 
  temperature 
  or 
  a 
  little 
  lower, 
  1540°. 
  In 
  this 
  

   case 
  no 
  liquid 
  is 
  formed 
  and 
  for 
  that 
  reason 
  the 
  crystals 
  are 
  

   not 
  as 
  typically 
  developed, 
  but 
  the 
  quadratic 
  section 
  of 
  kalio- 
  

  

  *See 
  Z. 
  Weyberg, 
  Centralblatt 
  Min., 
  p. 
  401, 
  1908. 
  

  

  