﻿378 
  Fenner 
  — 
  Stability 
  Relations 
  of 
  Silica 
  Minerals. 
  

  

  The 
  average 
  of 
  all 
  determinations 
  gives 
  practically 
  the 
  figure 
  

   575° 
  for 
  the 
  inversion-point 
  on 
  heating, 
  and 
  570° 
  for 
  the 
  point 
  

   on 
  cooling. 
  The 
  very 
  slight 
  variation 
  from 
  these 
  figures 
  given 
  

   by 
  any 
  sample, 
  whatever 
  its 
  mode 
  of 
  origin 
  or 
  previous 
  treat- 
  

   ment, 
  indicates 
  the 
  presence 
  of 
  but 
  one 
  sort 
  of 
  molecule 
  in 
  

   quartz-crystals, 
  but 
  an 
  element 
  of 
  doubt 
  enters 
  into 
  the 
  ques- 
  

   tion 
  because 
  of 
  the 
  anomalous 
  behavior 
  of 
  one 
  sample 
  not 
  

   listed 
  above. 
  This 
  material 
  was 
  from 
  a 
  quarry 
  in 
  basalt 
  at 
  

   Paterson, 
  N. 
  J., 
  and 
  was 
  associated 
  with 
  zeolites. 
  The 
  quartz 
  

   was 
  doubtless 
  deposited 
  from 
  aqueous 
  solution 
  at 
  a 
  compara- 
  

   tively 
  low 
  temperature. 
  The 
  material 
  collected 
  consisted 
  of 
  

   separate 
  crystals, 
  \ 
  cm. 
  in 
  length, 
  perfectly 
  clear 
  and 
  color- 
  

   less 
  at 
  top, 
  a 
  little 
  milky 
  at 
  base. 
  A 
  little 
  scaly 
  hematite 
  in 
  

   small 
  aggregates 
  was 
  present. 
  The 
  amount 
  of 
  material 
  

   unfortunately 
  was 
  not 
  large. 
  Although 
  the 
  crystals 
  all 
  pre- 
  

   sented 
  the 
  same 
  appearance, 
  it 
  appears 
  probable 
  that 
  some 
  

   were 
  of 
  normal 
  quartz, 
  as 
  the 
  results 
  from 
  different 
  samples 
  

   were 
  not 
  strictly 
  identical, 
  though 
  consistently 
  different 
  from 
  

   the 
  usual 
  values. 
  The 
  amethystine 
  quartz 
  listed 
  as 
  No. 
  7 
  in 
  

   Table 
  III 
  was 
  from 
  the 
  same 
  quarry 
  and 
  collected 
  at 
  the 
  same 
  

   time. 
  

  

  The 
  first 
  sample 
  of 
  the 
  abnormal 
  material 
  gave 
  for 
  inversion 
  

   points 
  567-3° 
  and 
  5564°. 
  A 
  second 
  gave 
  (a) 
  564-4° 
  and 
  559'8° 
  

   (b) 
  564-7° 
  and 
  559-7°. 
  After 
  heating 
  3 
  to 
  4 
  hours 
  over 
  blast 
  it 
  

   gave 
  564-5° 
  and 
  560-0°. 
  

  

  A 
  third 
  sample 
  was 
  then 
  taken 
  and 
  subjected 
  to 
  various 
  

   treatments 
  in 
  the 
  endeavor 
  to 
  obtain 
  evidence 
  as 
  to 
  the 
  cause 
  

   of 
  the 
  abnormal 
  results. 
  The 
  material 
  was 
  ground 
  very 
  fine 
  

   in 
  a 
  mortar 
  and 
  heated 
  with 
  concentrated 
  HC1 
  for 
  several 
  

   days 
  on 
  a 
  steam 
  bath. 
  It 
  was 
  then 
  washed 
  and 
  dried 
  and 
  

   inversion 
  determined. 
  Next 
  it 
  was 
  heated 
  at 
  1400° 
  for 
  17 
  

   minutes 
  and 
  inversion 
  again 
  determined. 
  The 
  results 
  were 
  as 
  

   follows 
  : 
  

  

  Untreated 
  material. 
  

  

  (a) 
  569-1° 
  558-2° 
  

  

  (b) 
  568-5° 
  5688 
  555',6° 
  556 
  9 
  

  

  Treated 
  with 
  HC1. 
  

  

  (a) 
  566-3° 
  560-5° 
  

  

  (b) 
  564-9° 
  5b52 
  559-9° 
  ° 
  b0 
  2 
  

  

  Treated 
  with 
  HC1 
  and 
  heated 
  to 
  1400°. 
  

  

  (a) 
  566-5° 
  561-8° 
  

  

  (b) 
  567-8° 
  56/ 
  l 
  557-8° 
  559 
  4 
  

  

  The 
  variations 
  are 
  not 
  large 
  and 
  apparently 
  the 
  treatment 
  

   to 
  which 
  the 
  material 
  has 
  been 
  subjected 
  has 
  not 
  effected 
  any 
  

   significant 
  change 
  in 
  the 
  inversion-point. 
  In 
  the 
  absence 
  of 
  

   evidence 
  no 
  definite 
  conclusion 
  can 
  be 
  drawn 
  as 
  to 
  the 
  cause 
  of 
  

   the 
  abnormality. 
  It 
  seems 
  most 
  probably 
  due 
  to 
  foreign 
  

  

  