﻿JV. 
  L. 
  Bowen 
  — 
  Sodium- 
  Potassium 
  Nephelite 
  s. 
  131 
  

  

  be 
  probably 
  a 
  residuum 
  from 
  the 
  granite 
  magma, 
  especially 
  

   rich 
  in 
  volatile 
  components. 
  From 
  the 
  present 
  work 
  we 
  

   obtain 
  definite 
  proof 
  of 
  a 
  fact 
  long 
  suspected, 
  viz. 
  the 
  exist- 
  

   ence 
  in 
  nephelite 
  of 
  the 
  molecule 
  KAlSi0 
  4 
  . 
  This 
  commonly 
  

   occurs 
  in 
  amounts 
  of 
  15 
  per 
  cent 
  or 
  more 
  and 
  is 
  the 
  same 
  mole- 
  

   cule 
  that 
  plays 
  a 
  fundamental 
  role 
  in 
  the 
  formation 
  of 
  the 
  

   micas. 
  At 
  the 
  same 
  time 
  it 
  is 
  not 
  to 
  be 
  expected 
  that 
  any 
  

   definite 
  solution 
  of 
  the 
  relation 
  between 
  two 
  such 
  rocks 
  will 
  be 
  

   accomplished 
  experimentally 
  except 
  in 
  aqueous 
  systems. 
  The 
  

   methods 
  of 
  attacking 
  such 
  systems, 
  combining 
  high 
  tempera- 
  

   tures 
  and 
  high 
  pressures, 
  have 
  been 
  worked 
  out 
  by 
  Morey" 
  

   and 
  his 
  investigations 
  will 
  be 
  extended 
  to 
  more 
  complex 
  sys- 
  

   tems 
  with 
  a 
  view 
  to 
  the 
  solution 
  of 
  this 
  and 
  related 
  problems. 
  

  

  The 
  existence 
  in 
  nephelite 
  of 
  an 
  average 
  of 
  more 
  than 
  10 
  

   per 
  cent 
  plagioclase 
  is 
  of 
  importance 
  in 
  connection 
  with 
  such 
  

   rocks 
  as 
  iolite 
  and 
  nephelinite. 
  Though 
  free 
  from 
  plagioclase 
  

   as 
  a 
  separate 
  mineral, 
  it 
  is 
  plain 
  that 
  one 
  cannot 
  consider 
  the 
  

   crystallization 
  of 
  the 
  magma 
  except 
  as 
  a 
  part 
  of 
  a 
  plagioclase- 
  

   bearing 
  system. 
  This 
  system 
  would 
  include 
  likewise 
  the 
  

   plagioclase 
  rocks 
  with 
  which 
  nephelinite 
  is 
  normally 
  associated 
  

   and 
  consideration 
  of 
  the 
  crystallization 
  of 
  such 
  a 
  system 
  serves 
  

   to 
  emphasize 
  the 
  relationship 
  of 
  the 
  types. 
  

  

  The 
  inversion 
  temperature 
  of 
  nephelite 
  does 
  not 
  prove 
  to 
  be 
  

   very 
  useful 
  for 
  the 
  determination 
  of 
  the 
  temperatures 
  of 
  for- 
  

   mation 
  of 
  minerals. 
  The 
  pure 
  compound 
  ]STaAlSi0 
  4 
  inverts 
  at 
  

   1248° 
  but 
  all 
  the 
  materials 
  that 
  it 
  takes 
  into 
  solid 
  solution 
  occa- 
  

   sion 
  a 
  sharp 
  rise 
  in 
  the 
  temperature 
  of 
  inversion. 
  In 
  order 
  to 
  

   appear 
  in 
  the 
  carnegieite 
  form, 
  separation 
  would 
  have 
  to 
  take 
  

   place 
  at 
  least 
  as 
  high 
  as 
  1325°-! 
  350°. 
  The 
  non-occurrence 
  of 
  

   carnegieite 
  may, 
  therefore, 
  be 
  considered 
  as 
  proof, 
  if 
  any 
  be 
  

   needed, 
  that 
  the 
  separation 
  of 
  nephelite 
  from 
  magmas 
  has 
  

   always 
  taken 
  place 
  at 
  temperatures 
  below 
  those 
  named. 
  

  

  The 
  occurrence 
  of 
  the 
  pseudo-hexagonal, 
  twinned 
  form 
  of 
  

   nephelite 
  in 
  the 
  nephelinite 
  described 
  by 
  Esch 
  is 
  not 
  to 
  be 
  con- 
  

   sidered 
  as 
  evidence 
  that 
  separation 
  took 
  place 
  at 
  high 
  temper- 
  

   atures. 
  It 
  is 
  true 
  that 
  this 
  form 
  is 
  believed 
  to 
  be 
  a 
  high 
  temper- 
  

   ature 
  form 
  of 
  potassium-rich 
  nephelites 
  or 
  kaliophilites 
  but, 
  

   unlike 
  carnegieite, 
  it 
  can 
  form 
  at 
  low 
  temperatures 
  also. 
  More- 
  

   over 
  it 
  will 
  persist 
  at 
  these 
  temperatures 
  just 
  as 
  the 
  forms 
  of 
  

   silica, 
  tridymite 
  and 
  cristobalite 
  do. 
  

  

  Summary. 
  

  

  The 
  present 
  paper 
  gives 
  the 
  results 
  of 
  an 
  experimental 
  

   investigation 
  of 
  the 
  binary 
  system 
  JSTaAlSiO.-KAlSiO,. 
  The 
  

   soda 
  compound 
  occurs 
  in 
  two 
  enantiotropic 
  forms, 
  nephelite 
  

  

  * 
  Jour. 
  Am. 
  Chem. 
  Soc, 
  xxxvi, 
  215, 
  1914. 
  

  

  