﻿Fennev 
  — 
  Stability 
  Relations 
  of 
  Silica 
  Minerals. 
  377 
  

  

  The 
  subject 
  of 
  this 
  inversion 
  has 
  been 
  so 
  thoroughly 
  studied 
  

   that 
  there 
  seemed 
  to 
  be 
  little 
  to 
  be 
  added. 
  The 
  chief 
  point 
  to 
  

   which 
  the 
  writer 
  directed 
  his 
  attention 
  was 
  the 
  possibility 
  of 
  

   finding 
  a 
  variation 
  in 
  the 
  temperature 
  of 
  inversion 
  similar 
  to 
  

   that 
  which 
  is 
  so 
  well 
  marked 
  in 
  cristobalite. 
  

  

  The 
  method 
  of 
  determining 
  inversion 
  temperatures 
  was 
  the 
  

   same 
  as 
  that 
  used 
  for 
  cristobalite 
  and 
  tridymite, 
  but 
  the 
  higher 
  

   temperature 
  prohibited 
  the 
  use 
  of 
  copper-constantan 
  thermo- 
  

   elements 
  and 
  the 
  standard 
  Pt 
  - 
  Pt 
  Rh 
  elements 
  were 
  substi- 
  

   tuted. 
  The 
  sensitiveness 
  of 
  these 
  is 
  only 
  about 
  one-fifth 
  that 
  

   of 
  copper-constantan 
  and 
  the 
  accuracy 
  of 
  determination 
  was 
  

   slightly 
  diminished, 
  nevertheless 
  very 
  satisfactory 
  results 
  were 
  

   obtained. 
  The 
  form 
  of 
  curve 
  is 
  shown 
  in 
  fig. 
  9. 
  

  

  In 
  general, 
  natural 
  quartz 
  of 
  different 
  modes 
  of 
  occurrence 
  

   was 
  employed, 
  but 
  artificial 
  material 
  obtained 
  by 
  the 
  conver- 
  

   sion 
  of 
  cristobalite 
  in 
  a 
  tungstate 
  melt 
  at 
  800°-835° 
  was 
  also 
  

   used, 
  and 
  in 
  addition 
  determinations 
  were 
  made 
  on 
  the 
  pure 
  

   quartz 
  of 
  the 
  Laboratory 
  stock 
  previously 
  heated 
  to 
  very 
  high 
  

   temperatures. 
  All 
  the 
  results 
  with 
  one 
  exception 
  were 
  almost 
  

   identical. 
  With 
  this 
  one 
  exception, 
  they 
  are 
  tabulated 
  below. 
  

  

  Table 
  III. 
  

   Inversion 
  Temperatures 
  of 
  Quartz. 
  

  

  Inversion 
  Eeversion 
  

  

  Material 
  used 
  on 
  heating 
  on 
  cooling 
  

  

  1. 
  Ground 
  quartz, 
  Laboratory 
  stock, 
  ) 
  (a) 
  576 
  -4° 
  ►-,,- 
  QO 
  570 
  'V 
  Kl 
  ~-. 
  KO 
  

  

  untreated 
  j 
  (b) 
  575-5° 
  °'° 
  y 
  572'3° 
  oa 
  ' 
  D 
  

  

  2. 
  Same, 
  heated 
  over 
  Bunsen 
  576*6° 
  

  

  3. 
  Same, 
  heated 
  11 
  minutes 
  at 
  1515°.. 
  I 
  [^ 
  |^|'.^ 
  5732° 
  ^'.^ 
  569*1° 
  

  

  4. 
  Same, 
  heated 
  10 
  minutes 
  at 
  1527°- 
  [ 
  K 
  ^o 
  A 
  ° 
  nan 
  1 
  a° 
  

  

  1543° 
  and 
  cooled 
  slowly 
  [ 
  °' 
  d4 
  0b 
  '* 
  y 
  

  

  5. 
  Same, 
  heated 
  20 
  hours 
  at 
  1200° 
  ± 
  574-7° 
  571-1° 
  

  

  6. 
  Quartz 
  phenocrysts 
  from 
  granite 
  ) 
  Rr>K 
  ao 
  Ka 
  c\ 
  no 
  

  

  near 
  Meissen.... 
  \ 
  5 
  ' 
  5 
  b 
  5b9 
  ' 
  7 
  

  

  7. 
  Amethystine 
  quartz 
  from 
  Paterson, 
  ) 
  ^7^-2° 
  <"ifiQ 
  q° 
  

  

  8. 
  Milky 
  quartz 
  from 
  Dutchess 
  Co., 
  N.Y. 
  575-1° 
  568-9° 
  

  

  9. 
  Crystals 
  of 
  water- 
  clear 
  quartz 
  from 
  ) 
  

  

  Moritz 
  Co., 
  N. 
  Y., 
  showing 
  right 
  V 
  574*5° 
  567*2° 
  

  

  trapezohedron 
  ) 
  

  

  10. 
  White 
  quartz 
  from 
  pegmatite 
  vein, 
  / 
  K 
  „ 
  A 
  a0 
  Ktyi 
  00 
  

   District 
  of 
  Columbia 
  \ 
  °' 
  4b 
  571 
  "^ 
  

  

  11. 
  Eose 
  quartz 
  from 
  near 
  Paris, 
  ) 
  (a) 
  574-4° 
  p- 
  7A1 
  o 
  

  

  Maine 
  f 
  (b) 
  573-9° 
  °' 
  4 
  i 
  569*5~° 
  

  

  12. 
  White 
  quartz 
  from 
  a 
  pegmatite 
  ) 
  KrrA 
  - 
  Q 
  Kan 
  00 
  

   vein, 
  Maine 
  f 
  °' 
  4t) 
  5by 
  "' 
  

  

  13. 
  Abnormal-looking 
  green 
  quartz 
  ) 
  „- 
  10 
  K 
  „ 
  n 
  00 
  

   from 
  Copper 
  Mt., 
  Alaska 
  f 
  * 
  14: 
  ' 
  1 
  5 
  ' 
  ^ 
  

  

  14. 
  Artificial 
  quartz 
  made 
  from 
  cristo- 
  j 
  (?> 
  ™'}° 
  M*% 
  

   balite 
  in 
  a 
  tungstate 
  melt 
  f 
  °> 
  ^.^ 
  57 
  ' 
  * 
  ™°.* 
  568 
  5 
  

  

  Average 
  574*9° 
  569*5° 
  

  

  