﻿Larsen 
  and 
  Hunt 
  — 
  T 
  anadiferous 
  jEgirites. 
  289 
  

  

  Aet. 
  XXYIII. 
  — 
  Two 
  Vanadiferous 
  ^Egirites 
  from 
  Libby 
  , 
  

   Montana 
  /* 
  by 
  Espee 
  S. 
  Laesen 
  and 
  W. 
  F. 
  Hunt. 
  

  

  InTEODECTION. 
  

  

  The 
  two 
  pyroxenes 
  described 
  in 
  this 
  paper 
  were 
  collected 
  by 
  

   Mr. 
  J. 
  T. 
  Pardee 
  of 
  the 
  United 
  States 
  Geological 
  Survey 
  in 
  

   the 
  Rainy 
  Creek 
  mining 
  district, 
  about 
  7 
  miles 
  northeast 
  

   of 
  Libby, 
  Lincoln 
  County, 
  Montana. 
  Later 
  Mr. 
  Ben. 
  M. 
  

   Thomas, 
  of 
  Libby, 
  Montana, 
  sent 
  the 
  authors 
  more 
  material. 
  

   ^Ve 
  are 
  indebted 
  to 
  these 
  gentlemen 
  for 
  the 
  excellent 
  specimens 
  

   and 
  for 
  information 
  about 
  the 
  occurrence 
  of 
  the 
  minerals. 
  

  

  The 
  two 
  minerals, 
  one 
  of 
  which 
  is 
  an 
  aegirite 
  and 
  the 
  other 
  

   an 
  aegirite-augite, 
  occur 
  in 
  veins 
  associated 
  with 
  quartz, 
  calcite, 
  

   microcline, 
  sulphides, 
  and 
  other 
  minerals. 
  The 
  aegirite 
  carries 
  

   nearly 
  -1 
  per 
  cent 
  of 
  Y 
  2 
  O 
  a 
  , 
  but 
  otherwise 
  its 
  chemical 
  composi- 
  

   tion 
  is 
  that 
  of 
  ordinary 
  aegirite. 
  The 
  crystal 
  measurements 
  are 
  

   also 
  in 
  close 
  agreement 
  with 
  those 
  of 
  aegirite; 
  the 
  form 
  i 
  [130] 
  

   is 
  new 
  for 
  aegirite. 
  The 
  mineral 
  is 
  deep 
  brown 
  in 
  color 
  and 
  its 
  

   optical 
  properties 
  differ 
  from 
  the 
  aegirite 
  generally 
  described 
  

   in 
  the 
  lower 
  index 
  of 
  refraction, 
  weaker 
  birefringence, 
  smaller 
  

   extinction 
  angle, 
  and 
  larger 
  axial 
  angle. 
  The 
  segirite-augite 
  

   was 
  found 
  only 
  in 
  fibrous 
  aggregates. 
  It 
  carries 
  nearly 
  3 
  per 
  

   cent 
  of 
  YX), 
  and 
  its 
  optical 
  properties 
  are 
  not 
  greatly 
  different 
  

   from 
  those 
  of 
  ordinary 
  aegirite-augite. 
  

  

  Occurrence 
  and 
  associations. 
  — 
  The 
  two 
  pyroxenes 
  occur 
  

   together 
  in 
  veins 
  which 
  were 
  probably 
  formed 
  under 
  deep- 
  

   seated 
  conditions 
  and 
  at 
  a 
  high 
  temperature. 
  Indeed, 
  they 
  

   have 
  some 
  resemblance 
  to 
  pegmatites. 
  White 
  to 
  milky, 
  

   granular 
  quartz 
  is 
  the 
  most 
  abundant 
  mineral 
  of 
  the 
  veins 
  ; 
  

   calcite, 
  the 
  pyroxene 
  and 
  microcline 
  feldspar 
  are 
  abundant 
  ; 
  

   pyrite, 
  pyrrhotite, 
  chalcopyrite, 
  galena, 
  sphalerite, 
  and 
  other 
  

   sulphides, 
  are 
  less 
  abundant 
  ; 
  fLuorite 
  is 
  present 
  ; 
  and 
  barite 
  

   was 
  recognized 
  in 
  one 
  specimen. 
  The 
  veins 
  show 
  rather 
  

   prominent 
  banding, 
  as 
  the 
  pyroxene 
  and 
  microcline 
  are 
  largely 
  

   confined 
  to 
  their 
  borders. 
  The 
  parts 
  of 
  the 
  vein 
  which 
  are 
  

   rich 
  in 
  either 
  pyroxene 
  are 
  commonly 
  also 
  rich 
  in 
  microcline 
  

   and 
  sulphides. 
  

  

  The 
  veins 
  occur 
  in 
  a 
  rather 
  coarse-grained 
  apatite-pyroxenite 
  

   which 
  is 
  chiefly 
  diopside 
  with 
  about 
  10 
  per 
  cent 
  of 
  apatite, 
  

   nearly 
  as 
  much 
  titaniferous 
  magnetite, 
  and 
  less 
  biotite. 
  This 
  

   rock 
  carries 
  0*12 
  per 
  cent 
  Y 
  2 
  3 
  . 
  Associated 
  with 
  it 
  are 
  soda- 
  

   syenites 
  and 
  nepheline-syenites. 
  On 
  each 
  side 
  of 
  the 
  veins 
  

   the 
  pvroxenite 
  is 
  altered 
  for 
  a 
  distance 
  of 
  from 
  an 
  inch 
  to 
  a 
  

  

  * 
  Published 
  by 
  permission 
  of 
  the 
  Director 
  of 
  the 
  United 
  States 
  Geological 
  

   Survey. 
  

  

  