﻿292 
  Larsen 
  and 
  Hunt 
  — 
  Yanadiferous 
  ^Egirites. 
  

  

  

  

  

  Table 
  I. 
  

  

  

  

  

  

  

  

  Crystal 
  Angle 
  

  

  of 
  JEgirite. 
  

  

  

  

  

  

  

  

  

  Observed 
  

  

  Brogger 
  

  

  711 
  

  

  • 
  m 
  

  

  = 
  (110) 
  

  

  (110) 
  = 
  

  

  

  87° 
  5' 
  

  

  87° 
  

  

  11' 
  

  

  m 
  

  

  : 
  a 
  

  

  = 
  (110) 
  : 
  

  

  (100) 
  = 
  

  

  

  46 
  29 
  

  

  46 
  

  

  241/2 
  

  

  m 
  

  

  b 
  

  

  = 
  (110) 
  

  

  (010) 
  = 
  

  

  

  43 
  39 
  

  

  43 
  

  

  351/2 
  

  

  f 
  

  

  f 
  

  

  = 
  (310) 
  

  

  (310) 
  = 
  

  

  

  38 
  47 
  

  

  38 
  

  

  36 
  

  

  f 
  

  

  a 
  

  

  = 
  (310) 
  

  

  : 
  (100) 
  = 
  

  

  

  19 
  7 
  

  

  19 
  

  

  18 
  

  

  / 
  

  

  m 
  

  

  = 
  (310) 
  

  

  (110)= 
  

  

  

  27 
  9 
  

  

  27 
  

  

  7 
  

  

  i 
  : 
  

  

  i 
  

  

  = 
  (130) 
  

  

  (130) 
  = 
  • 
  

  

  

  35 
  58 
  

  

  — 
  

  

  — 
  

  

  p 
  : 
  

  

  m 
  

  

  = 
  (101) 
  

  

  (110)= 
  

  

  

  100 
  33 
  

  

  100 
  

  

  19 
  

  

  p 
  : 
  

  

  a 
  

  

  = 
  (101) 
  

  

  (100) 
  = 
  

  

  

  75 
  38 
  

  

  74 
  

  

  56 
  

  

  frequently 
  been 
  recognized 
  on 
  the 
  diopside-augite 
  series, 
  where 
  

   the 
  corresponding 
  angle 
  is 
  35° 
  12'. 
  This 
  is 
  of 
  some 
  interest 
  as 
  

   it 
  will 
  be 
  shown 
  that 
  chemically 
  the 
  composition 
  can 
  be 
  so 
  in- 
  

   terpreted 
  as 
  to 
  show 
  the 
  presence 
  of 
  a 
  considerable 
  amount 
  of 
  

   diopside. 
  

  

  Physical 
  properties. 
  — 
  The 
  prismatic 
  cleavages 
  are 
  very 
  per- 
  

   fect—more 
  perfect 
  than 
  is 
  usual 
  in 
  segirite. 
  The 
  hardness 
  is 
  

   about 
  equal 
  to 
  that 
  of 
  ordinary 
  a^girite, 
  6 
  — 
  6*5 
  ; 
  the 
  specific 
  

   gravity 
  as 
  determined 
  by 
  the 
  pycnometer 
  method 
  is 
  355. 
  The 
  

   mineral 
  is 
  rather 
  strongly 
  magnetic 
  as 
  small 
  fragments 
  of 
  it 
  

   are 
  sensibly 
  affected 
  by 
  an 
  ordinary 
  pocket 
  magnet. 
  The 
  

   crystals 
  are 
  bright 
  and 
  lustrous 
  ; 
  the 
  color 
  is 
  nearly 
  black 
  in 
  

   thick 
  crystals, 
  but 
  thin 
  splinters 
  are 
  brown 
  and 
  translucent. 
  

  

  Optical 
  properties. 
  — 
  The 
  optical 
  properties 
  of 
  this 
  segirite 
  

   closely 
  resemble 
  those 
  of 
  the 
  segirite 
  from 
  Langesund 
  

   described 
  by 
  Brogger. 
  The 
  brown 
  color 
  is 
  more 
  prominent. 
  

   It 
  differs 
  from 
  other 
  segirite 
  described 
  in 
  the 
  lower 
  index 
  of 
  

   refraction, 
  weaker 
  birefringence, 
  smaller 
  extinction 
  angle, 
  

   larger 
  axial 
  angle, 
  and 
  marked 
  brown 
  color. 
  In 
  the 
  following 
  

   table 
  the 
  principal 
  optical 
  properties 
  of 
  the 
  vanadiferous 
  

   segirite 
  from 
  Libby, 
  Montana, 
  are 
  given 
  in 
  column 
  1, 
  and 
  for 
  

   comparison 
  the 
  data 
  of 
  Broggor 
  on 
  segirite 
  from 
  Langesund, 
  

   and 
  that 
  of 
  Wulfing 
  on 
  segirite 
  from 
  Langesund 
  are 
  given 
  : 
  

  

  Table 
  II. 
  

  

  Optical 
  Properties 
  of 
  JEgirite. 
  

  

  Larsen 
  

   Libby, 
  Mont. 
  

  

  a 
  = 
  1*745 
  ± 
  0-005 
  

   (i— 
  1-770 
  ± 
  0*005 
  

   y 
  = 
  1-782 
  ± 
  0-005 
  

   y-a 
  — 
  0-034 
  ± 
  0-002 
  

  

  X 
  

  

  1 
  

  

  0-034 
  

   2V 
  = 
  69° 
  

   c 
  - 
  1-4°,, 
  

  

  3 
  U 
  

   0-3' 
  

  

  Brogger 
  

   Langesund 
  

  

  1-753, 
  

  

  63°28' 
  

  

  ol° 
  

   2^- 
  

  

  tO 
  3i° 
  3 
  

  

  Wiilfing 
  

   Langesund 
  

  

  l-7630 
  v 
  

  

  7990j 
  

   8126, 
  

  

  0-0496 
  

   62°13' 
  

   4° 
  to 
  4 
  

  

  15'. 
  

  

  