﻿Fenner 
  — 
  Stability 
  Relations 
  of 
  Silica 
  Minerals. 
  331 
  

  

  Art. 
  XXXIV. 
  — 
  The 
  Stability 
  Relations 
  of 
  the 
  Silica 
  

   Minerals 
  / 
  by 
  Clarence 
  "N. 
  Fenner. 
  

  

  Introduction. 
  

  

  Determination 
  of 
  the 
  inversion 
  points 
  between 
  quartz 
  and 
  tridymite 
  

  

  and 
  between 
  tridymite 
  and 
  cristobalite. 
  

   The 
  appearance 
  of 
  unstable 
  phases. 
  

  

  Suggested 
  explanation 
  of 
  anomalous 
  results 
  previously 
  obtained. 
  

   Natural 
  occurrences 
  of 
  tridymite 
  and 
  cristobalite. 
  

   Effect 
  of 
  pressure 
  upon 
  the 
  quartz-tridymite 
  inversion. 
  

   Information 
  to 
  be 
  obtained 
  from 
  the 
  study 
  of 
  tridymite-bearing 
  

  

  rocks. 
  

   Physical 
  properties 
  of 
  artificial 
  quartz, 
  tridymite, 
  and 
  cristobalite. 
  

   Preparation 
  of 
  quartz 
  in 
  aqueous 
  solution. 
  

  

  General 
  observations 
  on 
  the 
  quartz-tridymite-cristobalite 
  inversions. 
  

   Low 
  temperature 
  inversions. 
  

   Eolations 
  of 
  chalcedony 
  to 
  other 
  forms 
  of 
  silica. 
  

   Fusion 
  of 
  cristobalite 
  and 
  quartz. 
  

   Summary. 
  

  

  Introduction. 
  

  

  Much 
  work 
  has 
  been 
  done 
  at 
  various 
  times 
  on 
  the 
  relations 
  

   between 
  the 
  different 
  forms 
  of 
  silica 
  which 
  are 
  found 
  as 
  natu- 
  

   ral 
  minerals, 
  and 
  the 
  literature 
  of 
  the 
  subject 
  is 
  extensive. 
  A 
  

   portion 
  of 
  what 
  has 
  been 
  written 
  has 
  beeD 
  based 
  upon 
  labora- 
  

   tory 
  experiments, 
  a 
  portion 
  upon 
  observation 
  o'f 
  natural 
  occur- 
  

   rences, 
  and 
  still 
  a 
  third 
  portion 
  upon 
  theoretical 
  considerations. 
  

   Each 
  method 
  of 
  attack, 
  when 
  properly 
  applied, 
  is 
  a 
  legitimate 
  

   means 
  of 
  attempting 
  to 
  arrive 
  at 
  a 
  solution 
  of 
  a 
  problem, 
  and 
  

   in 
  the 
  paper 
  which 
  follows, 
  each 
  will 
  be 
  resorted 
  to 
  to 
  a 
  certain 
  

   degree, 
  but 
  chief 
  stress 
  will 
  be 
  laid 
  upon 
  the 
  results 
  attained 
  

   by 
  experimental 
  investigation. 
  

  

  In 
  spite 
  of 
  the 
  work 
  done 
  upon 
  the 
  problem, 
  the 
  results 
  pre- 
  

   viously 
  attained 
  can 
  hardly 
  be 
  considered 
  to 
  be 
  satisfactory. 
  

   The 
  conclusions 
  reached 
  from 
  the 
  experimental 
  side 
  were 
  not 
  

   concordant 
  ; 
  those 
  derived 
  from 
  observation 
  of 
  natural 
  occur- 
  

   rences 
  indicated 
  the 
  relations 
  in 
  a 
  general 
  way, 
  but 
  were 
  not 
  

   sufficiently 
  explicit 
  and 
  also 
  contained 
  contradictions 
  which 
  no 
  

   theoretical 
  consideration 
  was 
  able 
  to 
  clear 
  up. 
  For 
  these 
  rea- 
  

   sons, 
  the 
  Geophysical 
  Laboratory 
  took 
  up 
  the 
  problem 
  several 
  

   years 
  ago, 
  and 
  the 
  work 
  done 
  at 
  that 
  time 
  resulted 
  in 
  consider- 
  

   able 
  advance 
  in 
  our 
  knowledge 
  of 
  the 
  relations 
  of 
  the 
  several 
  

   forms. 
  In 
  the 
  first 
  publication 
  in 
  which 
  the 
  matter 
  was 
  dis- 
  

   cussed,* 
  the 
  inversion 
  point 
  between 
  quartz 
  and 
  tridymite 
  was 
  

   placed 
  at 
  approximately 
  800° 
  and 
  the 
  melting 
  point 
  of 
  tridy- 
  

   mite 
  (or, 
  more 
  properly, 
  the 
  change 
  from 
  the 
  crystalline 
  to 
  the 
  

   amorphous 
  condition) 
  was 
  considered 
  to 
  be 
  about 
  1600°. 
  At 
  

  

  * 
  The 
  Lime-Silica 
  Series 
  of 
  Minerals, 
  A. 
  L. 
  Day, 
  E. 
  S. 
  Shepherd 
  and 
  F. 
  E. 
  

   Wright, 
  this 
  Journal, 
  (4), 
  xxii, 
  265-302, 
  1906. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XXXVI, 
  No. 
  214.— 
  October, 
  1913. 
  

   22 
  

  

  