﻿JOURNAL 
  

  

  OF 
  THE 
  

  

  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  

  

  Vol. 
  12 
  May 
  4, 
  1922 
  No. 
  9 
  

  

  PETROLOGY, 
  — 
  The 
  development 
  of 
  pressure 
  in 
  magmas 
  as 
  a 
  result 
  

   of 
  crystallization 
  ? 
  George 
  W. 
  Morey, 
  Geophysical 
  Laboratory. 
  

  

  The 
  explanation 
  of 
  the 
  phenomena 
  which 
  take 
  place 
  in 
  the 
  cooling 
  

   of 
  molten 
  magmas, 
  whether 
  forming 
  intrusive 
  masses 
  or 
  extrusive 
  

   flows, 
  is 
  one 
  of 
  the 
  principal 
  functions 
  of 
  petrology. 
  To 
  such 
  magmas 
  

   all 
  of 
  the 
  laws 
  of 
  the 
  physical 
  chemistry 
  of 
  mixtures 
  apply, 
  and 
  the 
  

   phenomena 
  met 
  with 
  as 
  these 
  mixtures 
  cool 
  and 
  solidify 
  under 
  the 
  

   conditions 
  found 
  in 
  nature 
  are 
  the 
  result 
  of 
  the 
  action 
  of 
  these 
  physico- 
  

   chemical 
  laws. 
  The 
  elucidation 
  of 
  these 
  phenomena 
  in 
  terms 
  of 
  the 
  

   known 
  laws 
  of 
  physical 
  chemistry 
  is 
  made 
  difficult 
  both 
  by 
  the 
  extreme 
  

   complexity 
  of 
  the 
  natural 
  mixtures 
  and 
  by 
  the 
  general 
  lack 
  of 
  knowl- 
  

   edge 
  as 
  to 
  the 
  theoretical 
  relationships 
  of 
  mixtures 
  containing 
  not 
  only 
  

   non-volatile 
  components 
  such 
  as 
  the 
  silicate 
  minerals 
  but 
  also 
  vola-' 
  

   tile 
  components 
  far 
  above 
  their 
  critical 
  temperatures, 
  such 
  as 
  carbon 
  

   dioxide 
  and 
  water. 
  

  

  In 
  this 
  note 
  attention 
  will 
  be 
  directed 
  to 
  certain 
  relationships 
  be- 
  

   tween 
  the 
  temperature 
  and 
  composition 
  and 
  the 
  vapor 
  pressure 
  of 
  the 
  

   volatile 
  component, 
  and 
  especially 
  to 
  the 
  relations 
  between 
  these 
  

   quantities 
  at 
  temperatures 
  approximating 
  to 
  the 
  temperature 
  of 
  an- 
  

   hydrous 
  fusion 
  of 
  the 
  mineral 
  components, 
  and 
  at 
  very 
  considerable 
  

   pressure. 
  At 
  temperatures 
  near 
  that 
  at 
  which 
  crystallization 
  begins 
  

   a 
  liquid 
  silicate 
  mixture 
  containing 
  but 
  a 
  small 
  amount 
  of 
  volatile 
  

   component 
  may 
  exert 
  but 
  a 
  comparatively 
  small 
  vapor 
  pressure, 
  but 
  

   as 
  crystallization 
  proceeds 
  with 
  falling 
  temperature 
  the 
  pressure 
  of 
  the 
  

   volatile 
  components 
  will 
  increase 
  at 
  a 
  rapid 
  rate 
  : 
  so 
  rapid 
  that 
  a 
  pres- 
  

   sure 
  many 
  times 
  the 
  original 
  pressure 
  may 
  result 
  from 
  the 
  crystalliza- 
  

   tion 
  of 
  but 
  a 
  small 
  proportion 
  of 
  the 
  non-volatile 
  material. 
  This 
  re- 
  

   lation 
  holds 
  true 
  whether 
  the 
  original 
  liquid 
  mixture 
  consists 
  of 
  water 
  

   and 
  a 
  low 
  melting 
  salt 
  such 
  as 
  KNO3, 
  or 
  of 
  water 
  and 
  other 
  volatile 
  

   substances 
  with 
  the 
  usual 
  non-volatile 
  magmatic 
  constituents; 
  the 
  

  

  • 
  Received 
  March 
  27, 
  1922. 
  

  

  219 
  

  

  