﻿abt,7 
  THE 
  MINERAL 
  EDDINGSITE 
  ROSS 
  AND 
  SHANNON 
  15 
  

  

  the 
  present 
  work 
  there 
  were 
  purified 
  and 
  analyzed, 
  more 
  or 
  less 
  

   completely, 
  six. 
  samples 
  of 
  clean 
  crystalline 
  iddingsite 
  from 
  as 
  many 
  

   localities 
  together 
  with 
  cryptocrystalline 
  materials 
  associated 
  with 
  

   two 
  of 
  the 
  crystalline 
  materials 
  analyzed. 
  

  

  In 
  most 
  cases 
  the 
  samples 
  of 
  purified 
  material 
  available 
  amounted 
  

   to 
  only 
  0.25 
  gram. 
  These 
  samples 
  were 
  separated 
  by 
  the 
  use 
  of 
  a 
  

   powerful 
  electromagnet 
  and 
  heavy 
  solutions 
  from 
  igneous 
  rocks 
  in 
  

   which 
  the 
  iddingsites 
  formed 
  grains 
  seldom 
  exceeding 
  2 
  millimeters 
  

   in 
  diameter. 
  In 
  general 
  the 
  practice 
  was 
  to 
  crack 
  the 
  iddingsite- 
  

   bearing 
  rock 
  into 
  small 
  pieces 
  with 
  a 
  hammer 
  and 
  gouge 
  out 
  the 
  

   visible 
  iddingsite 
  with 
  a 
  sharp 
  steel 
  point 
  yielding 
  a 
  product 
  of 
  high 
  

   iddingsite 
  content 
  for 
  subsequent 
  treatment. 
  This 
  was 
  crushed 
  and 
  

   screened 
  to 
  uniform 
  size, 
  the 
  dust 
  removed, 
  and 
  the 
  material 
  sepa- 
  

   rated 
  magnetically 
  and 
  with 
  methylene 
  iodide 
  gravity 
  solutions. 
  

  

  The 
  mineral, 
  as 
  established 
  by 
  previous 
  investigators, 
  is 
  insoluble 
  

   in 
  acids, 
  but 
  upon 
  digestion 
  in 
  hot 
  hydrochloric 
  acid 
  yields 
  up 
  its 
  

   iron 
  and 
  probably 
  its 
  other 
  bases, 
  leaving 
  decolorized 
  scales. 
  This 
  

   phenomenon 
  has 
  been 
  interpreted 
  as 
  evidence 
  indicating 
  that 
  the 
  

   iron 
  is 
  not 
  essential 
  to 
  the 
  composition 
  but 
  is 
  present 
  as 
  staining 
  films 
  

   of 
  limonite 
  or 
  hematite. 
  The 
  fallacy 
  of 
  this 
  reasoning 
  is 
  patent 
  when 
  

   it 
  is 
  recalled 
  that 
  many 
  minerals 
  behave 
  thus, 
  even 
  so 
  common 
  a 
  

   substance 
  as 
  biotite 
  leaving 
  decolorized 
  scales 
  of 
  silica 
  retaining 
  

   the 
  original 
  form 
  and 
  optical 
  properties 
  of 
  the 
  mineral, 
  when 
  

   digested 
  in 
  hot 
  concentrated 
  sulphuric 
  acid. 
  Few 
  would 
  venture 
  to 
  

   suggest, 
  from 
  this 
  observation, 
  that 
  the 
  iron 
  of 
  biotite 
  is 
  nonessential 
  

   or 
  extraneous. 
  

  

  The 
  analytical 
  results 
  on 
  the 
  iddingsites 
  are 
  given 
  in 
  the 
  following 
  

   tables 
  : 
  

  

  1. 
  Crystalline 
  iddingsite 
  from 
  Race 
  Creek, 
  Colo. 
  

  

  2. 
  Crystalline 
  iddingsite 
  from 
  La 
  Jara 
  Creek, 
  Colo. 
  

  

  3. 
  Cryptocrystalline 
  material 
  associated 
  with 
  the 
  iddingsite 
  from 
  

   La 
  Jara 
  Creek 
  of 
  the 
  preceding 
  analysis. 
  

  

  4. 
  Crystalline 
  iddingsite 
  from 
  Bernards 
  Ferry, 
  Owyhee 
  County, 
  

   Idaho. 
  Specimen 
  collected 
  by 
  Lindgren. 
  

  

  5. 
  Ciw^ptocrystalline 
  material 
  associated 
  with 
  the 
  preceding 
  id- 
  

   dingsite 
  from 
  Bernards 
  Ferry, 
  Idaho. 
  

  

  6. 
  Crystalline 
  iddingsite 
  from 
  South 
  Elk 
  Creek, 
  Colo. 
  

  

  7. 
  Crystalline 
  iddingsite 
  from 
  Gato 
  Creek, 
  Conejos 
  quadrangle, 
  

   Colo. 
  

  

  8. 
  Crystalline 
  iddingsite 
  of 
  high 
  index 
  from 
  Rio 
  Brazos, 
  N. 
  Mex. 
  

   Original 
  analysis. 
  

  

  9. 
  Iddingsite 
  from 
  Rio 
  Brazos. 
  Preceding 
  analysis 
  corrected 
  for 
  

   impurities 
  and 
  recalculated 
  to 
  100 
  per 
  cent. 
  

  

  