﻿ADIRONDACK 
  MAGNETIC 
  IRON 
  ORES 
  I5I 
  

  

  of 
  the 
  most 
  recent 
  investigations; 
  the 
  work 
  of 
  Penfield 
  and 
  Foote 
  1 
  

   affords 
  in 
  fact 
  quite 
  convincing 
  evidence 
  of 
  its 
  validity. 
  According 
  

   to 
  that 
  formula 
  it 
  contains 
  theoretically 
  FeO, 
  46.75 
  per 
  cent 
  and 
  

   Ti0 
  2 
  , 
  53.25 
  per 
  cent. 
  There 
  is 
  always 
  some 
  Fe 
  2 
  3 
  present 
  and 
  

   usually 
  more 
  or 
  less 
  MgO. 
  The 
  latter 
  replaces 
  the 
  FeO, 
  while 
  

   the 
  former 
  substitutes 
  probably 
  for 
  the 
  ilmenite 
  molecule, 
  since 
  the 
  

   close 
  similarity 
  in 
  the 
  structure 
  and 
  crystal 
  form 
  of 
  hematite 
  and 
  

   ilmenite 
  indicates 
  that 
  they 
  are 
  practically 
  isomorphous. 
  A 
  general 
  

   formula 
  for 
  ilmenite, 
  accordingly, 
  is 
  Fe 
  Ti0 
  3 
  .w 
  Fe 
  2 
  3 
  . 
  

  

  The 
  fact 
  that 
  the 
  titaniferous 
  ores 
  are 
  not 
  homogeneous 
  aggregates 
  

   is 
  sometimes 
  apparent 
  from 
  a 
  macroscopic 
  examination. 
  The 
  mag- 
  

   netite 
  may 
  be 
  recognized 
  by 
  its 
  parting 
  planes 
  parallel 
  to 
  the 
  octa- 
  

   hedron, 
  the 
  grains 
  always 
  breaking 
  with 
  smooth 
  surfaces. 
  It 
  is 
  

   the 
  most 
  abundant 
  constituent 
  as 
  a 
  rule. 
  In 
  the 
  intervals 
  between 
  

   the 
  grains 
  are 
  particles 
  of 
  brighter 
  metallic 
  luster 
  that 
  show 
  rough 
  

   fracture. 
  These 
  are 
  only 
  slightly 
  attracted 
  by 
  the 
  magnet 
  and 
  

   when 
  isolated 
  prove 
  to 
  be 
  ilmenite. 
  

  

  To 
  bring 
  out 
  the 
  physical 
  relations 
  of 
  the 
  minerals 
  the 
  method 
  

   of 
  preparing 
  polished 
  surfaces 
  and 
  etching 
  with 
  acid 
  can 
  be 
  used 
  

   to 
  good 
  advantage. 
  2 
  Some 
  results 
  obtained 
  with 
  Adirondack 
  

   ores 
  are 
  shown 
  herewith 
  [pi. 
  14]. 
  The 
  photographs 
  were 
  taken 
  

   directly 
  with 
  a 
  camera 
  in 
  ordinary 
  light, 
  as 
  the 
  texture 
  of 
  the 
  ores 
  

   is 
  sufficiently 
  coarse 
  to 
  be 
  revealed 
  without 
  the 
  use 
  of 
  the 
  micro- 
  

   scope. 
  It 
  will 
  be 
  seen 
  that 
  there 
  is 
  a 
  good 
  contrast 
  between 
  the 
  

   magnetite 
  and 
  ilmenite, 
  the 
  former 
  being 
  dulled 
  and 
  pitted 
  by 
  the 
  

   solvent 
  action 
  of 
  the 
  acid, 
  while 
  the 
  latter 
  retains 
  the 
  brilliancy 
  

   imparted 
  to 
  it 
  by 
  polishing 
  unimpaired. 
  From 
  the 
  etched 
  surfaces 
  

   a 
  fairly 
  close 
  estimate 
  of 
  the 
  richness 
  of 
  the 
  ore 
  may 
  be 
  formed 
  by 
  

   comparing 
  the 
  relative 
  areas 
  occupied 
  by 
  the 
  ore 
  and 
  gangue 
  min- 
  

   erals, 
  though 
  the 
  latter 
  do 
  not 
  appear 
  distinctly 
  in 
  the 
  photograph. 
  

  

  In 
  the 
  specimens 
  that 
  have 
  been 
  examined 
  the 
  magnetite 
  and 
  

   ilmenite 
  are 
  distinguishable 
  without 
  difficulty. 
  There 
  is 
  a 
  clear 
  

   separation 
  of 
  the 
  particles 
  and 
  no 
  notable 
  tendency 
  toward 
  inter- 
  

   growth 
  or 
  inclusion 
  on 
  the 
  part 
  of 
  either. 
  The 
  boundaries 
  are 
  sharp. 
  

   Both 
  minerals 
  belong 
  to 
  the 
  same 
  order 
  of 
  crystallization, 
  though 
  

   the 
  ilmenite 
  seems 
  to 
  have 
  begun 
  to 
  form 
  somewhat 
  earlier 
  than 
  

  

  1 
  Note 
  Concerning 
  the 
  Composition 
  of 
  Ilmenite. 
  Am. 
  Jour. 
  Sci. 
  154. 
  

   ser. 
  4. 
  1897. 
  p. 
  108. 
  

  

  2 
  Pieces 
  of 
  the 
  ore 
  an 
  inch 
  or 
  so 
  in 
  diameter 
  are 
  cut 
  with 
  a 
  diamond 
  saw 
  

   or 
  ground 
  down 
  to 
  a 
  comparatively 
  smooth 
  surface 
  on 
  a 
  wheel 
  such 
  as 
  is 
  

   used 
  for 
  preparing 
  rock 
  sections. 
  The 
  surfaces 
  are 
  then 
  polished 
  with 
  fine 
  

   emery, 
  finishing 
  off 
  with 
  putty 
  powder 
  on 
  cloth. 
  The 
  etching 
  is 
  performed 
  

   by 
  submersion 
  in 
  a 
  20 
  per 
  cent 
  HC1 
  solution 
  for 
  half 
  an 
  hour. 
  

  

  