﻿38 
  Eahins 
  — 
  Analyses 
  of 
  Astrophyllite 
  and 
  Tscheffhinite. 
  

  

  of 
  reddish 
  -brown 
  color, 
  it 
  is 
  doubly 
  refracting, 
  but 
  not 
  strongly 
  

   pleochroic, 
  and 
  cannot 
  be 
  identified 
  with 
  any 
  of 
  the 
  substances 
  

   already 
  mentioned. 
  Adjacent 
  to 
  these 
  bands, 
  and 
  replacing 
  

   the 
  amorphous 
  material 
  to 
  varying 
  distances 
  is 
  still 
  another 
  

   substance, 
  in 
  general 
  appearance 
  similar 
  to 
  the 
  prismatic 
  min- 
  

   eral, 
  but 
  evidently 
  different 
  as 
  it 
  shows 
  no 
  very 
  marked 
  absorp- 
  

   tion. 
  This 
  mineral 
  is 
  also 
  strongly 
  pleochroic, 
  varying 
  from 
  

   yellow-brown 
  to 
  chestnut 
  -brown. 
  All 
  of 
  it 
  in 
  the 
  sections 
  

   seems 
  to 
  have 
  a 
  uniform 
  crystallographic 
  orientation, 
  the 
  cause 
  

   of 
  this 
  uniformity 
  not 
  being 
  apparent. 
  Its 
  relations 
  to 
  the 
  

   amorphous 
  substance 
  are 
  similar 
  to 
  those 
  which 
  I 
  have 
  observed 
  

   in 
  several 
  instances 
  between 
  crystalline 
  allanite 
  and 
  the 
  amorph- 
  

   ous 
  variety." 
  

  

  The 
  microscopical 
  examination 
  having 
  shown 
  this 
  tscheff- 
  

   kinite 
  to 
  be 
  such 
  a 
  mixture, 
  it 
  became 
  desirable 
  to 
  examine 
  

   others 
  in 
  the 
  same 
  way. 
  

  

  The 
  only 
  one 
  available 
  for 
  this 
  purpose 
  was 
  that 
  analyzed 
  

   by 
  Price, 
  a 
  specimen 
  of 
  which 
  is 
  in 
  the 
  National 
  Museum 
  col- 
  

   lection. 
  This 
  specimen 
  has 
  the 
  same 
  general 
  appearance 
  

   and 
  banded 
  structure 
  as 
  my 
  own. 
  Chips 
  were 
  taken 
  from 
  it 
  

   for 
  sections 
  which 
  Mr. 
  Cross 
  examined 
  and 
  found 
  to 
  be 
  in 
  

   every 
  respect 
  similar 
  to 
  the 
  other, 
  about 
  the 
  only 
  noticeable 
  

   difference 
  being 
  in 
  Price's 
  material 
  a 
  somewhat 
  greater 
  devel- 
  

   opment 
  of 
  the 
  opaque 
  ochreous 
  decomposition 
  product 
  of 
  the 
  

   transparent 
  amorphous 
  substance 
  than 
  in 
  mine, 
  and 
  a 
  lesser 
  

   development 
  of 
  the 
  colorless 
  minerals. 
  

  

  Taking 
  into 
  consideration 
  the 
  results 
  of 
  this 
  work, 
  and 
  the 
  

   manifest 
  contradictions 
  of 
  most 
  of 
  the 
  earlier 
  analyses, 
  it 
  seems 
  

   reasonable 
  to 
  conclude 
  that, 
  unless 
  one 
  of 
  the 
  earlier 
  analyses 
  

   can 
  be 
  shown 
  to 
  have 
  been 
  made 
  on 
  pure 
  material, 
  the 
  so-called 
  

   tscheffkinite 
  is 
  not 
  a 
  mineral 
  in 
  any 
  strict 
  construction 
  of 
  the 
  

   word, 
  but 
  merely 
  a 
  mixture 
  ; 
  the 
  structure 
  of 
  the 
  chemically 
  

   complex 
  body 
  or 
  bodies 
  evidently 
  its 
  basis 
  being 
  a 
  problem 
  to 
  

   be 
  elucidated 
  in 
  the 
  future 
  when 
  purer 
  material 
  may 
  be 
  found. 
  

  

  Laboratory, 
  U. 
  S. 
  Geological 
  Survey, 
  

   Washington, 
  D. 
  C, 
  March, 
  1891. 
  

  

  