﻿CLAYS 
  OF 
  XEW 
  YORK 
  503 
  

  

  MINERALOGY 
  OF 
  CLAYS 
  

  

  Tlie 
  number 
  of 
  mineral 
  species 
  wHch 
  may 
  exist 
  in 
  clays 
  is 
  very 
  

   great, 
  and 
  depends 
  partly 
  on 
  tlie 
  mineralogic 
  composition 
  of 
  the 
  

   parent 
  rock, 
  and 
  the 
  extent 
  to 
  which 
  decomposition 
  has 
  proceeded 
  

   in 
  the 
  clay 
  mass. 
  

  

  The 
  characters 
  of 
  the 
  common 
  minerals 
  found 
  in 
  clays 
  together 
  

   with 
  their 
  more 
  important 
  features, 
  are 
  here 
  given, 
  arranged 
  ap- 
  

   proximately 
  in 
  the 
  order 
  of 
  their 
  abundance. 
  Any 
  one 
  of 
  these 
  

   may 
  however 
  at 
  times 
  become 
  a 
  predominating 
  constituent. 
  

  

  Kaolinite. 
  Formula: 
  Al^Og, 
  'i 
  810-2, 
  '-^ 
  ^^2^^, 
  or 
  silica 
  (SiO^) 
  

  

  46.3^, 
  alumina 
  (Al 
  A) 
  39.8.^ 
  , 
  water 
  (H2O) 
  13.9/^ 
  

   « 
  

   This 
  is 
  a 
  white, 
  pearly 
  mineral, 
  crystallizing 
  in 
  the 
  monoclinic 
  

  

  system, 
  the 
  crystals 
  presenting 
  the 
  fonoi 
  of 
  small 
  hexagonal 
  plates. 
  

  

  Its 
  specific 
  gravity 
  is 
  2.2-2.6; 
  its 
  hardness 
  2-2.5. 
  It 
  is 
  naturally 
  

  

  white 
  in 
  color 
  and 
  a 
  mass 
  of 
  it 
  is 
  plastic 
  when 
  wet, 
  but 
  very 
  slightly 
  

  

  so. 
  The 
  occurrence 
  of 
  kaolinite 
  in 
  crvstals 
  has 
  been 
  noted 
  from 
  

  

  xJ 
  

  

  National 
  belle 
  mine. 
  Red 
  Mountain, 
  Col. 
  (H. 
  Reus<?h, 
  Jalirh. 
  f. 
  

   miyieralogie, 
  1887, 
  2:70) 
  and 
  from 
  Anglesey 
  (A. 
  Dick, 
  Min. 
  

   mag. 
  1876, 
  8 
  :15). 
  A 
  microscopic 
  examination 
  shows 
  the 
  plates 
  of 
  

   kaolinite 
  collected 
  in 
  little 
  bunches. 
  Their 
  separation 
  by 
  grinding 
  

   increases 
  the 
  plasticity.^ 
  

  

  If 
  kaolin 
  be 
  formed 
  into 
  briquets, 
  of 
  the 
  same 
  shape 
  as 
  those 
  

   used 
  in 
  testing 
  cement, 
  its 
  tensile 
  strength, 
  as 
  determined 
  by 
  pulling 
  

   these 
  briquets 
  apart 
  in 
  a 
  testing 
  macliine, 
  is 
  usually 
  5-15 
  pounds 
  

   the 
  square 
  inch 
  — 
  a 
  very 
  low 
  degree 
  compared 
  with 
  the 
  tensile 
  

   strength 
  of 
  more 
  plastic 
  clays. 
  

  

  Kaolinite 
  is 
  nearly 
  infusible, 
  but 
  a 
  slight 
  addition 
  of 
  fusible 
  

   impurities 
  lowers 
  its 
  refractoriness. 
  

  

  Many 
  kaolins 
  contain 
  very 
  minute 
  scales 
  of 
  white 
  mica, 
  which 
  

   it 
  would 
  be 
  difficult 
  to 
  distinguish 
  under 
  the 
  microscope 
  from 
  

   kaolinite. 
  Since 
  white 
  mica 
  in 
  a 
  very 
  finely 
  divided 
  condition 
  is 
  

  

  1 
  Clays 
  of 
  New 
  Jersey, 
  N. 
  J. 
  geol. 
  sur. 
  1878. 
  G. 
  H. 
  Cook. 
  

  

  