﻿CLAYS 
  OF 
  NEW 
  YORK 
  525 
  

  

  Silica 
  

  

  Three 
  types 
  of 
  silica 
  may 
  be 
  recognized 
  in 
  clay: 
  1) 
  quartz; 
  2) 
  

   that 
  which 
  is 
  combined 
  with 
  alumina 
  and 
  water 
  in 
  kaolinite; 
  3) 
  that 
  

   which 
  is 
  combined 
  with 
  one 
  or 
  more 
  bases 
  in 
  silicate 
  minerals. 
  In 
  

   chemical 
  analysis 
  the 
  first 
  and 
  third 
  are 
  sometimes 
  grouped 
  together 
  

   under 
  the 
  head 
  of 
  " 
  sand/' 
  or 
  at 
  times 
  erroneously 
  spoken 
  of 
  as 
  

   " 
  free 
  '^ 
  silica. 
  The 
  silica 
  included 
  under 
  the 
  term 
  sand 
  is 
  prac- 
  

   tically 
  insoluble 
  in 
  sulfuric 
  acid 
  and 
  caustic 
  soda. 
  This 
  fact 
  is 
  

   utilized 
  in 
  the 
  rational 
  analysis 
  of 
  clay 
  to 
  extract 
  the 
  kaolinite 
  or 
  

   clay 
  substance, 
  which 
  is 
  soluble 
  in 
  sulfuric 
  acid 
  and 
  caustic 
  soda. 
  

  

  Quartz 
  is 
  present 
  in 
  every 
  clay 
  so 
  far 
  as 
  analysis 
  shows, 
  but 
  in 
  

   variable 
  amounts. 
  Cook 
  -^ 
  found 
  a 
  minimum 
  of 
  .2^, 
  and 
  gives 
  

   5^ 
  as 
  the 
  average 
  in 
  the 
  Woodbridge 
  fire 
  clays. 
  Wheeler 
  ^ 
  gives 
  

   the 
  igiinimum 
  as 
  .5^ 
  in 
  the 
  fiint 
  clays, 
  and 
  the 
  sand 
  percentage 
  

   as 
  20^-43^ 
  in 
  the 
  St 
  Louis 
  fire 
  clays 
  and 
  20;^-50^ 
  in 
  the 
  Loess 
  clays. 
  

   27 
  samples 
  of 
  Alabama 
  clays 
  analyzed 
  by 
  the 
  Avriter 
  contained 
  from 
  

   5^ 
  to 
  50^ 
  of 
  insoluble 
  residue 
  mostly 
  quartz.^ 
  

  

  In 
  70 
  ISTorth 
  Caroliria^ 
  clays 
  there 
  were 
  from 
  15.05^ 
  to 
  70.43^ 
  iur 
  

   soluble 
  residue; 
  while 
  in 
  three 
  samples, 
  of 
  which 
  a 
  rational 
  analysis 
  

   was 
  made, 
  the 
  percentage 
  of 
  sand 
  was 
  from 
  24.55^ 
  to 
  56.58;^. 
  The 
  

   quartz 
  varied 
  from 
  16.58;^ 
  to 
  49.06^, 
  with 
  the 
  feldspathic 
  residue 
  

   from 
  7.52^ 
  to 
  16.05^. 
  

  

  In 
  European 
  clays 
  similar 
  variations 
  in 
  the 
  amount 
  of 
  sand 
  and 
  

   quartz 
  are 
  observable. 
  Thus 
  a 
  clay 
  from 
  Hainstadt, 
  Germany 
  

   contains 
  67.03^ 
  of 
  quartz 
  (Ziegler 
  Kalender. 
  Berlin 
  1896), 
  while 
  

   one 
  from 
  Ruppersdorf 
  showed 
  .26^. 
  (Seger's 
  Ges. 
  Schrift. 
  p. 
  891) 
  

  

  The 
  following 
  table 
  srives 
  the 
  variation 
  in 
  the 
  total 
  silica 
  in 
  four 
  

   types 
  of 
  clay 
  : 
  

  

  Quality 
  Min. 
  Max. 
  Aver. 
  

  

  Brick 
  clays 
  34.35 
  90.877 
  59.27 
  

  

  Pottery 
  clays 
  45 
  . 
  06 
  86.98 
  45 
  . 
  83 
  

  

  Fireclays 
  34.40 
  96.79 
  54.304 
  

  

  Kaolins 
  32.44 
  81.18 
  55.44 
  

  

  IN. 
  J. 
  geol. 
  sur. 
  1878. 
  Clays 
  of 
  New 
  Jersey, 
  p. 
  213. 
  

  

  2 
  Mo. 
  geol. 
  sur. 
  1896. 
  11: 
  54. 
  

  

  3 
  Ala. 
  geol. 
  sur. 
  1900. 
  Bulletin 
  no. 
  6. 
  

  

  4N. 
  C. 
  geol. 
  sur. 
  1898. 
  Bulletin 
  no. 
  13, 
  p. 
  24. 
  

  

  