﻿140 
  Vander 
  Meiden 
  — 
  Two 
  So-called 
  Halloy 
  sites. 
  

  

  Art. 
  XIV. 
  — 
  A 
  Study 
  of 
  Two 
  So-called 
  Halloysites 
  from 
  

   Georgia 
  and 
  Alabama 
  / 
  by 
  P. 
  A. 
  yakder 
  Meulen. 
  

  

  The 
  term 
  halloysite 
  is 
  usually 
  applied 
  to 
  a 
  massive, 
  clay-like 
  

   or 
  earthy 
  mineral, 
  with 
  a 
  conchoidal 
  fracture, 
  waxy 
  luster, 
  and 
  

   made 
  up 
  essentially 
  of 
  silica, 
  alumina, 
  and 
  water. 
  According 
  

   to 
  Le 
  Chatelier 
  the 
  composition 
  probably 
  is 
  2H 
  2 
  0, 
  A1 
  2 
  3 
  , 
  

   2Si0 
  2 
  4- 
  Aq., 
  or 
  silica, 
  43*5 
  ; 
  alumina, 
  36*9 
  ; 
  water, 
  19*6. 
  

  

  Analyses 
  of 
  this 
  type 
  of 
  clay 
  have 
  been 
  published 
  from 
  time 
  

   to 
  time, 
  many 
  of 
  which 
  show 
  similarity 
  to 
  the 
  theoretic 
  com- 
  

   position, 
  but 
  no 
  other 
  tests 
  have 
  usually 
  been 
  recorded 
  on 
  the 
  

   samples 
  thus 
  analyzed. 
  

  

  Some 
  time 
  ago, 
  Prof. 
  Pies 
  placed 
  at 
  my 
  disposal, 
  for 
  chem- 
  

   ical 
  investigation, 
  two 
  samples 
  of 
  sedimentary 
  clay, 
  which 
  have 
  

   gone 
  under 
  the 
  name 
  of 
  halloysite. 
  Both 
  possessed 
  the 
  usually 
  

   accepted 
  properties 
  of 
  halloysite.* 
  They 
  were 
  almost 
  pure 
  

   white, 
  had 
  a 
  more 
  or 
  less 
  conchoidal 
  fracture, 
  and 
  became 
  

   somewhat 
  translucent 
  when 
  placed 
  in 
  water. 
  

  

  The 
  first 
  of 
  these 
  came 
  from 
  Chattooga 
  County, 
  Georgia. 
  

   On 
  close 
  examination, 
  it 
  was 
  observed 
  to 
  have 
  on 
  the 
  surface, 
  

   and 
  lining 
  cracks, 
  a 
  number 
  of 
  very 
  fine 
  needle-like 
  crystals, 
  and 
  

   in 
  some 
  of 
  these 
  cracks 
  also 
  a 
  small 
  amount 
  of 
  a 
  black 
  powdery 
  

   substance 
  which 
  proved 
  to 
  be 
  an 
  oxide 
  of 
  manganese. 
  The 
  clay 
  

   itself 
  was 
  entirely 
  homogeneous 
  under 
  the 
  microscope, 
  appear- 
  

   ing 
  either 
  amorphous 
  or 
  exceedingly 
  fine-grained, 
  and 
  free 
  

   from 
  the 
  small 
  crystals 
  mentioned 
  above. 
  

  

  A 
  number 
  of 
  the 
  largest 
  of 
  these 
  crystals 
  were 
  selected 
  and 
  

   tested 
  by 
  blowpipe 
  methods. 
  They 
  were 
  infusible, 
  and 
  became 
  

   opaque 
  on 
  heating, 
  had 
  a 
  hardness 
  of 
  about 
  three, 
  gave 
  much 
  

   water 
  in 
  the 
  closed 
  tube, 
  contained 
  no 
  silica, 
  but 
  much 
  alumina. 
  

   These 
  tests 
  indicated 
  that 
  the 
  crystals 
  were 
  hydrargillite. 
  

  

  Several 
  of 
  the 
  best 
  of 
  these, 
  about 
  1 
  mm. 
  in 
  length 
  and 
  0*1 
  mm. 
  

   in 
  diameter, 
  were 
  selected, 
  and 
  the 
  angles 
  between 
  faces 
  in 
  the 
  

   prism 
  zone 
  measured. 
  The 
  angles 
  corresponded 
  with 
  those 
  of 
  

   hydrargillite, 
  described 
  by 
  Broggerf 
  on 
  crystals 
  of 
  ISTorwegian 
  

   material. 
  The 
  end 
  faces 
  were 
  so 
  small 
  as 
  to 
  render 
  measure- 
  

   ment 
  impossible. 
  The 
  indices 
  of 
  refraction 
  determined 
  by 
  the 
  

   minimum 
  deviation 
  method 
  were 
  found 
  to 
  be 
  oc 
  = 
  /3 
  = 
  1*554 
  

   and 
  7 
  = 
  1*576. 
  These 
  values 
  are 
  somewhat 
  higher 
  than 
  those 
  

   obtained 
  by 
  Brogger. 
  

  

  A 
  sample 
  of 
  the 
  clay, 
  free 
  from 
  crystals, 
  and 
  also 
  from 
  the 
  

   black 
  oxide 
  of 
  manganese, 
  was 
  finely 
  ground 
  and 
  analyzed. 
  

   The 
  specific 
  gravity 
  of 
  the 
  fine 
  powder 
  was 
  determined 
  by 
  the 
  

   Dycnometer 
  method, 
  the 
  air 
  being 
  removed 
  by 
  means 
  of 
  a 
  

  

  *Dana, 
  p. 
  688, 
  6th 
  ed. 
  fZeitschr. 
  Kryst., 
  xvi, 
  45. 
  

  

  