﻿DEC. 
  4, 
  1922 
  WATSON 
  : 
  VEJIN 
  OF 
  RUTILE-ILMENITE 
  451 
  

  

  grains 
  frequently 
  show 
  shadow 
  extinction, 
  but 
  less 
  often 
  is 
  there 
  evi- 
  

   dence 
  of 
  peripheral 
  shattering 
  or 
  granulation. 
  

  

  Rutile. 
  — 
  The 
  rutile 
  is 
  developed 
  in 
  elongated 
  prismatic 
  crystals 
  of 
  

   dark 
  red-brown 
  color 
  up 
  to 
  6V2 
  cm. 
  (2^/i6 
  inches) 
  long 
  and 
  1 
  cm. 
  

   (^/i6 
  inch) 
  broad. 
  The 
  prism 
  faces 
  are 
  usually 
  vertically 
  striated 
  and 
  

   in 
  case 
  of 
  the 
  larger 
  ones 
  are 
  deeply 
  furrowed. 
  Terminal 
  crystal 
  faces 
  

   are 
  absent 
  and 
  twin 
  crystals 
  are 
  rare. 
  The 
  rutile 
  is 
  locally 
  distributed 
  

   through 
  the 
  quartz 
  matrix 
  in 
  clusters 
  of 
  prismatic 
  crystals, 
  and 
  as 
  

   scattered 
  single 
  crystals. 
  Thin 
  films 
  or 
  wedges 
  of 
  quartz 
  sometimes 
  

   part 
  crystals 
  for 
  more 
  than 
  half 
  their 
  length. 
  When 
  the 
  rutile 
  

   crystals 
  are 
  broken 
  from 
  the 
  matrix, 
  the 
  quartz 
  surfaces 
  are 
  smooth, 
  

   almost 
  polished, 
  and 
  preserve 
  completely 
  the 
  angles 
  and 
  striations 
  of 
  

   the 
  rutile 
  prism 
  faces. 
  The 
  crystals 
  are 
  usually 
  straight 
  but 
  curved 
  

   ones 
  sometimes 
  occur. 
  

  

  In 
  thin 
  sections 
  under 
  the 
  microscope 
  the 
  rutile 
  is 
  brownish 
  yellow 
  

   and 
  without 
  noticeable 
  pleochroism. 
  Cleavage 
  is 
  usually 
  well 
  devel- 
  

   oped 
  but 
  twinning 
  is 
  rare. 
  Much 
  of 
  the 
  rutile 
  appears 
  to 
  be 
  fresh, 
  

   but 
  some 
  of 
  it 
  shows 
  clouded 
  surfaces 
  indicating 
  slight 
  alteration. 
  The 
  

   rutile 
  is 
  partly 
  intergrown 
  with 
  and 
  partly 
  altered 
  to 
  ilmenite, 
  rela- 
  

   tionships 
  which 
  are 
  discussed 
  below. 
  A 
  chemical 
  analysis 
  of 
  the 
  rutile 
  

   is 
  given 
  in 
  column 
  I 
  of 
  Table 
  I. 
  

  

  Ilmenite. 
  — 
  This 
  mineral 
  exhibits 
  no 
  unusual 
  microscopic 
  characters. 
  

   Occasional 
  inclusions 
  of 
  quartz 
  occur, 
  but 
  those 
  of 
  rutile 
  are 
  more 
  

   frequent. 
  Like 
  the 
  rutile 
  it 
  is 
  usually 
  fresh, 
  but 
  much 
  of 
  it 
  shows 
  

   partial 
  alteration, 
  chiefly 
  about 
  the 
  boarders 
  and 
  along 
  cleavage 
  and 
  

   fracture 
  directions, 
  probably 
  to 
  leucoxene. 
  The 
  most 
  interesting 
  

   feature 
  of 
  the 
  ilmenite 
  is 
  its 
  intergowth 
  relation 
  to 
  rutile. 
  

  

  Microscopic 
  study 
  of 
  thin 
  sections 
  shows 
  that 
  the 
  two 
  minerals 
  

   rarely 
  occur 
  as 
  separate 
  individuals, 
  but 
  are 
  usually 
  intergrown 
  

   with 
  the 
  characteristic 
  prismatic 
  habit 
  of 
  rutile. 
  This 
  relationship 
  

   has 
  frequently 
  been 
  observed 
  by 
  the 
  writer 
  in 
  formless 
  grains 
  and 
  

   masses 
  of 
  rutile, 
  but 
  rarely 
  to 
  such 
  a 
  degree 
  in 
  perfectly 
  formed 
  pris- 
  

   matic 
  crustals 
  of 
  rutile. 
  It 
  is 
  well 
  brought 
  out 
  chemically 
  in 
  the 
  analy- 
  

   sis 
  given 
  in 
  column 
  II 
  of 
  Table 
  I. 
  The 
  analysis 
  was 
  made 
  on 
  what 
  was 
  

   assumed, 
  after 
  careful 
  examination 
  to 
  be 
  a 
  single 
  individual 
  of 
  ilmen- 
  

   ite, 
  but 
  on 
  recasting 
  the 
  analysis 
  in 
  the 
  usual 
  way, 
  it 
  is 
  clear 
  that 
  the 
  

   specimen 
  was 
  composed 
  of 
  a 
  mechanical 
  mixture 
  of 
  rutile 
  and 
  ilmenite, 
  

   with 
  the 
  former 
  predominating. 
  

  

  Rutile-ilmenite 
  relationships. 
  — 
  Microscopic 
  study 
  of 
  thin 
  sections 
  

  

  