﻿Fenner 
  — 
  Stability 
  Relations 
  of 
  Silica 
  Minerals. 
  333 
  

  

  berger,* 
  in 
  consideration 
  of 
  the 
  evidence 
  which 
  he 
  believed 
  to 
  

   exist 
  for 
  the 
  precipitation 
  of 
  quartz 
  from 
  magmas 
  at 
  tempera- 
  

   tures 
  as 
  high 
  as 
  1000°, 
  had 
  expressed 
  the. 
  opinion 
  that 
  the 
  

   transformation 
  quartz-tridymite 
  might 
  perhaps 
  be 
  monotropic. 
  

  

  The 
  low 
  temperature 
  inversion 
  of 
  a 
  into 
  ft 
  quartz, 
  of 
  a-ft 
  

   tridymite, 
  and 
  of 
  a-ft 
  cristobalite, 
  was 
  described 
  in 
  the 
  later 
  

   paper 
  from 
  this 
  Laboratory, 
  to 
  which 
  reference 
  has 
  been 
  made. 
  

   The 
  velocity 
  with 
  which 
  these 
  reactions 
  occur, 
  compared 
  with 
  

   the 
  reluctance 
  with 
  which 
  quartz 
  inverts 
  into 
  tridymite 
  or 
  

   cristobalite, 
  had 
  been 
  noted 
  as 
  a 
  very 
  striking 
  phenomenon, 
  

   for 
  which 
  no 
  explanation 
  could 
  be 
  suggested. 
  Further 
  investi- 
  

   gation 
  of 
  these 
  reactions 
  seemed 
  desirable. 
  

  

  These 
  problems 
  were 
  held 
  in 
  abeyance 
  by 
  the 
  Laboratory 
  

   for 
  some 
  time 
  in 
  the 
  stress 
  of 
  other 
  work. 
  At 
  the 
  first 
  oppor- 
  

   tunity, 
  however, 
  they 
  were 
  again 
  taken 
  up 
  in 
  the 
  hope 
  that 
  

   with 
  the 
  advantage 
  of 
  the 
  knowledge 
  gained 
  from 
  previous 
  

   investigations, 
  the 
  problem 
  might 
  be 
  cleared 
  up. 
  The 
  specific 
  

   points 
  which 
  were 
  obscure 
  and 
  for 
  which 
  a 
  solution 
  was 
  

   desired, 
  were 
  the 
  following: 
  

  

  1. 
  Are 
  the 
  relations 
  between 
  the 
  forms 
  chalcedony, 
  quartz, 
  

   tridymite, 
  and 
  cristobalite 
  monotropic 
  or 
  enantiotropic 
  ? 
  

  

  2. 
  If 
  enantiotropic, 
  what 
  are 
  the 
  fields 
  of 
  stability 
  of 
  each, 
  

   and 
  what 
  are 
  the 
  inversion 
  points 
  ? 
  

  

  3. 
  What 
  is 
  the 
  explanation 
  of 
  the 
  observed 
  fact 
  that 
  both 
  in 
  

   natural 
  occurrences 
  and 
  in 
  the 
  results 
  of 
  experimental 
  work, 
  

   quartz, 
  tridymite, 
  and 
  cristobalite 
  appear 
  to 
  have 
  been 
  formed 
  

   at 
  times 
  almost 
  simultaneously, 
  or 
  at 
  least 
  under 
  conditions 
  

   under 
  which 
  not 
  all 
  could 
  be 
  stable 
  ? 
  

  

  4. 
  What 
  is 
  the 
  reason 
  for 
  the 
  remarkable 
  velocity 
  of 
  the 
  

   a-ft 
  inversions 
  of 
  quartz, 
  tridymite, 
  and 
  cristobalite 
  as 
  com- 
  

   pared 
  with 
  the 
  slowness 
  of 
  transformation 
  of 
  each 
  of 
  these 
  

   minerals 
  into 
  one 
  of 
  the 
  others? 
  

  

  5. 
  To 
  which 
  form 
  of 
  silica 
  does 
  the 
  previously 
  determined 
  

   melting 
  point 
  belong 
  ? 
  

  

  To 
  these 
  may 
  be 
  added 
  a 
  sixth 
  question 
  which 
  arose 
  in 
  the 
  

   course 
  of 
  the 
  work 
  and, 
  from 
  its 
  theoretical 
  importance, 
  

   demanded 
  solution. 
  

  

  6. 
  Is 
  the 
  temperature 
  of 
  inversion 
  of 
  a 
  into 
  ft 
  cristobalite 
  a 
  

   fixed 
  point 
  and 
  is 
  its 
  apparent 
  variability 
  due 
  to 
  some 
  such 
  

   recognized 
  factor 
  as 
  impurity 
  of 
  material 
  or 
  lag, 
  or 
  is 
  it 
  actually 
  

   a 
  movable 
  point 
  and 
  therefore 
  an 
  extraordinary 
  type 
  of 
  phe- 
  

   nomenon 
  ? 
  

  

  To 
  some 
  of 
  these 
  questions 
  the 
  present 
  investigation 
  has 
  

   supplied 
  categorical 
  answers. 
  To 
  others 
  the 
  direction 
  in 
  which 
  

   experimental 
  work 
  points 
  for 
  the 
  explanation 
  brings 
  one 
  upon 
  

   debatable 
  ground 
  and 
  caution 
  must 
  be 
  used 
  lest 
  positive 
  con- 
  

  

  * 
  J. 
  Koenigsberger, 
  Neues 
  Jahrb., 
  Beilageband, 
  xxxii, 
  113, 
  1911. 
  

  

  