﻿76 
  Warren, 
  Allan 
  and 
  Conner 
  — 
  A 
  Titaniferous 
  Augite. 
  

  

  One 
  of 
  the 
  series 
  of 
  rods 
  lies 
  parallel 
  to 
  the 
  vertical 
  crystal- 
  

   lographic 
  axis 
  ; 
  the 
  other 
  follows 
  a 
  direction 
  which 
  makes 
  an 
  

   angle 
  of 
  about 
  74° 
  with 
  the 
  first 
  series 
  (on 
  sections 
  parallel 
  to 
  

   (010)) 
  and 
  appears, 
  therefore, 
  to 
  follow 
  the 
  direction 
  of 
  the 
  edge, 
  

   001-010. 
  In 
  the 
  absence 
  of 
  well-defined 
  cleavage 
  lines, 
  the 
  

   first 
  set 
  of 
  inclusions 
  can 
  be 
  used 
  very 
  well 
  to. 
  measure 
  the 
  

   extinction 
  directions 
  on. 
  In 
  view 
  of 
  the 
  black 
  color 
  and 
  opac- 
  

   ity 
  of 
  the 
  inclusions, 
  and 
  the 
  very 
  high 
  titanium 
  content 
  of 
  the 
  

   augite, 
  it 
  seems 
  pretty 
  certain 
  that 
  the 
  inclusions 
  are 
  ilmenite. 
  

   It 
  may 
  be 
  noted, 
  that 
  when 
  some 
  of 
  the 
  inclusions 
  are 
  viewed 
  

   on 
  end, 
  they 
  appear 
  to 
  be 
  minute 
  tubes, 
  filled 
  with 
  some 
  trans- 
  

   parent 
  material. 
  The 
  augite 
  grains 
  also 
  contain 
  some 
  minute 
  

   black 
  inclusions 
  which 
  lie 
  at 
  random, 
  and 
  also 
  a 
  few 
  larger, 
  

   irregular 
  or 
  rounded 
  masses 
  pf 
  what 
  seems 
  to 
  be 
  also 
  ilmenite. 
  

   The 
  pleochrism 
  is 
  rather 
  strong, 
  and 
  is 
  as 
  follows 
  : 
  — 
  

  

  a 
  = 
  reddish 
  or 
  pinkish-brown 
  (with 
  a 
  violet 
  shade 
  in 
  thick 
  

   fragments). 
  

  

  (3 
  = 
  reddish 
  or 
  pinkish-brown 
  (with 
  a 
  violet 
  shade 
  in 
  thick 
  

   fragments). 
  

  

  y 
  — 
  pale, 
  bright 
  yellow 
  (a 
  little 
  brownish 
  shade 
  in 
  thick 
  frag- 
  

   ments). 
  

  

  The 
  absorption 
  is 
  : 
  — 
  a 
  ^ 
  /3 
  "> 
  y. 
  

  

  The 
  extinction 
  was 
  measured 
  against 
  the 
  series 
  of 
  black 
  

   inclusions 
  lying 
  parallel 
  to 
  the 
  vertical 
  axis 
  in 
  several 
  thin- 
  

   sections 
  of 
  grains 
  showing 
  a 
  maximum 
  double 
  refraction, 
  and 
  

   was 
  found 
  to 
  range 
  for 
  7 
  ^ 
  c 
  f 
  from 
  41'9° 
  to 
  42*6°, 
  or 
  an 
  aver- 
  

   age 
  of 
  42*3°. 
  This 
  value 
  was 
  obtained 
  by 
  measuring 
  from 
  the 
  

   direction 
  of 
  the 
  lines 
  of 
  inclusions 
  to 
  the 
  position 
  of 
  maximum 
  

   darkness 
  in 
  white 
  light. 
  Like 
  many 
  titaniferous 
  augites 
  this 
  

   pyroxene 
  has 
  a 
  very 
  strong 
  dispersion 
  of 
  the 
  bisectrices, 
  and 
  

   anomalous 
  interference 
  colors 
  appear 
  on 
  either 
  side 
  of 
  the 
  posi- 
  

   tion 
  of 
  maximum 
  darkness. 
  In 
  the 
  present 
  case, 
  the 
  change 
  

   was 
  quite 
  sharp, 
  and 
  experiment 
  showed 
  that 
  the 
  results 
  

   obtained 
  in 
  this 
  way 
  were 
  more 
  consistent 
  than 
  were 
  those 
  

   obtained 
  by 
  using 
  monochromatic 
  lights. 
  

  

  The 
  interference 
  figures, 
  obtained 
  in 
  convergent 
  light, 
  show 
  

   a 
  very 
  strong, 
  inclined 
  dispersion 
  ; 
  — 
  red 
  greater 
  than 
  blue. 
  

   One 
  of 
  the 
  hyperbolas 
  appears 
  black, 
  while 
  the 
  other 
  consists 
  

   of 
  a 
  strong, 
  red, 
  inner 
  band 
  (convex 
  side) 
  and 
  an 
  equally 
  

   strong, 
  blue 
  band 
  on 
  the 
  concave 
  side. 
  The 
  width 
  of 
  the 
  two 
  

   colored 
  curves 
  covers 
  together 
  about 
  five 
  divisions 
  on 
  the 
  

   micrometer 
  scale 
  used, 
  which 
  is 
  equivalent 
  to 
  about 
  9° 
  angular. 
  

   Two 
  sections 
  were 
  found 
  which 
  were 
  nearly 
  normal 
  to 
  the 
  

   acute, 
  positive 
  bisectrix, 
  and 
  with 
  these 
  sections 
  the 
  optic 
  angle 
  

   in 
  the 
  air 
  was 
  measured 
  under 
  the 
  microscope 
  using 
  the 
  

   Wright 
  micrometer 
  scale. 
  On 
  account 
  of 
  the 
  breadth 
  and 
  

   lack 
  of 
  sharpness 
  of 
  the 
  hyperbolae, 
  both 
  in 
  white 
  light 
  and 
  

  

  