﻿78 
  Warren, 
  Allan 
  and 
  Conner 
  — 
  A 
  Titaniferous 
  Augite. 
  

  

  A 
  search 
  of 
  the 
  literature 
  relative 
  to 
  the 
  chemical 
  composi- 
  

   tion 
  of 
  the 
  augites 
  has 
  so 
  far 
  failed 
  to 
  find 
  any 
  which 
  are 
  very 
  

   close 
  to 
  the 
  one 
  under 
  consideration. 
  The 
  nearest 
  approach 
  is 
  

   found 
  in 
  an 
  augite 
  from 
  near 
  Rio 
  de 
  Janeiro, 
  analyzed 
  by 
  

   Hunter 
  and 
  described 
  by 
  Rosenbusch.* 
  The 
  latter 
  gives 
  its 
  

   properties 
  as 
  follows 
  : 
  — 
  Extinction 
  7 
  on 
  </, 
  40° 
  ; 
  dispersion 
  

   strong 
  ; 
  pleochrism, 
  (3 
  = 
  7 
  = 
  reddish- 
  violet, 
  a 
  = 
  yellow- 
  rose. 
  

  

  While 
  the 
  Ice 
  River 
  augite 
  is 
  much 
  higher 
  in 
  titanium 
  and 
  

   contains 
  no 
  alkalies, 
  there 
  is 
  otherwise 
  considerable 
  similarity 
  

   in 
  the 
  composition 
  of 
  the 
  two. 
  In 
  both, 
  the 
  silica 
  is 
  rather 
  

   low, 
  the 
  alumina, 
  ferric 
  iron 
  and 
  lime 
  are 
  high, 
  as 
  is 
  also 
  the 
  

   titanium. 
  The 
  latter 
  is 
  very 
  high 
  in 
  the 
  Ice 
  River 
  variety, 
  

   although 
  it 
  is 
  true, 
  that 
  some 
  part 
  of 
  the 
  titanium 
  is 
  present 
  in 
  

   the 
  form 
  of 
  the 
  rod-like 
  inclusions, 
  and 
  not 
  in 
  the 
  augite 
  itself. 
  

   It 
  is 
  impossible 
  to 
  say 
  how 
  much 
  Ti() 
  2 
  should 
  be 
  deducted 
  from 
  

   the 
  augite, 
  but 
  if 
  it 
  amounts 
  to 
  as 
  much 
  as 
  one 
  or 
  even 
  two 
  

   per 
  cent, 
  which 
  is 
  not 
  improbable, 
  it 
  would 
  still 
  leave 
  the 
  

   titanium 
  high. 
  A 
  combination 
  of 
  the 
  various 
  oxides 
  into 
  

   groups 
  yields 
  the 
  following 
  : 
  — 
  

  

  Ice 
  River 
  Augite. 
  Rio 
  de 
  Janeiro 
  Augite. 
  

  

  Si0 
  2 
  + 
  Ti0 
  2 
  = 
  0-757 
  0:777 
  

  

  RO 
  + 
  H 
  2 
  =0-755 
  0-785 
  ( 
  + 
  R 
  2 
  0) 
  

  

  R 
  2 
  O 
  s 
  =0-125 
  0-101 
  

  

  Si0 
  2 
  + 
  TiO, 
  : 
  R 
  2 
  O 
  s 
  : 
  RO 
  + 
  H 
  2 
  = 
  Si0 
  2 
  + 
  Ti0 
  2 
  : 
  R 
  2 
  3 
  : 
  RO 
  + 
  R 
  2 
  = 
  

  

  6 
  : 
  0-99 
  :5-91 
  7 
  : 
  7*08 
  : 
  0-91 
  

  

  The 
  titanium 
  has 
  all 
  been 
  included, 
  which 
  in 
  the 
  case 
  of 
  the 
  

   Ice 
  River 
  augite 
  unquestionably 
  makes 
  it 
  somewhat 
  too 
  high. 
  

   The 
  water 
  and 
  alkalies 
  are 
  here 
  included 
  with 
  the 
  RO. 
  It 
  is 
  

   noticeable 
  that, 
  as 
  might 
  be 
  expected, 
  the 
  relative 
  proportions 
  

   of 
  the 
  R0 
  2 
  and 
  RO 
  are 
  about 
  equal. 
  The 
  ratio 
  of 
  the 
  R0 
  2 
  in 
  

   the 
  one 
  augite 
  is 
  6:1, 
  and 
  in 
  the 
  other, 
  7:1, 
  or 
  nearly 
  so, 
  thus 
  

   bringing 
  out 
  a 
  rather 
  sharp 
  distinction 
  between 
  them. 
  

  

  It 
  has 
  occurred 
  to 
  the 
  authors, 
  that 
  at 
  the 
  time 
  of 
  crystalli- 
  

   zation 
  of 
  the 
  augite, 
  the 
  ilmenite 
  molecule, 
  RTi0 
  3 
  , 
  analogous 
  

   to 
  the 
  metasilicate 
  molecule, 
  RSi0 
  3 
  , 
  may 
  have 
  crystallized 
  

   isomorphously 
  with 
  it, 
  and 
  subsequently 
  becoming 
  unstable 
  in 
  

   that 
  state, 
  have 
  separated 
  out 
  — 
  unmixed. 
  In 
  any 
  case 
  the 
  tita- 
  

   nium 
  would 
  be 
  combined 
  with 
  the 
  RO 
  (FeO), 
  and 
  hence 
  would 
  

   not 
  affect 
  the 
  relative 
  values 
  of 
  the 
  ratio, 
  R0 
  2 
  : 
  RO, 
  as 
  calcu- 
  

   lated. 
  It 
  would 
  still 
  leave 
  the 
  excess 
  of 
  R 
  2 
  3 
  in 
  the 
  Ice 
  River 
  

   mineral, 
  as 
  compared 
  with 
  the 
  other, 
  as 
  marked 
  as 
  before. 
  

  

  In 
  conclusion 
  it 
  may 
  be 
  said 
  that 
  the 
  augite 
  described 
  above 
  

   differs 
  in 
  its 
  microscopic 
  and 
  chemical 
  characteristics 
  from 
  any 
  

   augite 
  known 
  to 
  the 
  writers 
  and 
  is 
  believed 
  to 
  be 
  of 
  interest 
  in 
  

   extending 
  somewhat 
  our 
  knowledge 
  of 
  the 
  titaniferous 
  augites. 
  

  

  Geological 
  Department, 
  Massachusetts 
  Institute 
  of 
  Technology, 
  

   Cambridge, 
  Mass., 
  August, 
  1916. 
  

  

  *Tsch. 
  Min. 
  Petr. 
  Mitt., 
  xi, 
  p. 
  460. 
  This 
  augite 
  occurred 
  in 
  a 
  monchi- 
  

   quite 
  dike 
  in 
  gneiss 
  at 
  Rio 
  de 
  Duro, 
  Sera 
  de 
  Tingua, 
  near 
  Rio 
  de 
  Janeiro. 
  

  

  