﻿Eakins 
  — 
  Analyses 
  of 
  Astrophyllite 
  and 
  Tscheffkinite. 
  37 
  

  

  formula, 
  a 
  result 
  quite 
  in 
  accordance 
  with 
  the 
  evidence 
  furn- 
  

   ished 
  by 
  the 
  microscopical 
  examination 
  of 
  sections. 
  For 
  this 
  

   purpose 
  chips 
  were 
  taken 
  showing 
  both 
  bands, 
  but 
  as 
  in 
  the 
  

   case 
  of 
  the 
  chemical 
  analysis, 
  they 
  were 
  seen 
  to 
  be 
  practically 
  

   the 
  same. 
  

  

  I. 
  II. 
  

  

  

  Analysis. 
  

  

  Molecular 
  

   ratio. 
  

  

  Analysis. 
  

  

  Molecular 
  

   ratio. 
  

  

  Ta 
  2 
  6 
  

  

  0-08 
  

  

  

  0-08 
  

  

  

  Si0 
  2 
  

  

  20-21 
  

  

  •337 
  

  

  21-49 
  

  

  •358 
  

  

  Ti0 
  2 
  

  

  18-78 
  

  

  •235 
  

  

  1899 
  

  

  •237 
  

  

  Zr0 
  o 
  

  

  *■.(?) 
  

  

  

  tr.(?) 
  

  

  

  Tho; 
  

  

  0-85 
  

  

  •003 
  

  

  0-75 
  

  

  •003 
  

  

  (Y, 
  Er) 
  2 
  3 
  

  

  1-82* 
  

  

  •006 
  

  

  l-64f 
  

  

  •005 
  

  

  (La, 
  Di) 
  2 
  3 
  

  

  19-72 
  

  

  •059 
  

  

  17-16 
  

  

  •052 
  

  

  Ce 
  2 
  3 
  

  

  20-05 
  

  

  •061 
  

  

  19-08 
  

  

  •058 
  

  

  Al 
  2 
  O 
  s 
  

  

  3-60 
  

  

  •035 
  

  

  3-65 
  

  

  •036 
  

  

  Fe 
  2 
  3 
  

  

  1-88 
  

  

  •012 
  

  

  2-89 
  

  

  •018 
  

  

  FeO 
  

  

  6-91 
  

  

  •096 
  

  

  5-92 
  

  

  •082 
  

  

  CaO 
  

  

  4-05 
  

  

  •072 
  

  

  5-24 
  

  

  •094 
  

  

  MaO 
  

  

  0-55 
  

  

  •014 
  

  

  48 
  

  

  •012 
  

  

  Na„0 
  

  

  0-06 
  

  

  •001 
  

  

  0-04 
  

  

  •001 
  

  

  H,0 
  

  

  0-94 
  

  

  •052 
  

  

  2-06 
  

  

  •114 
  

  

  99-50 
  

   Specific 
  gravity, 
  4*33 
  at 
  27°. 
  

  

  • 
  99-47 
  

   Specific 
  gravity, 
  4/38 
  at 
  22°-2. 
  

  

  I 
  am 
  indebted 
  to 
  Mr. 
  Whitman 
  Cross, 
  of 
  the 
  IT. 
  S. 
  Geolog- 
  

   ical 
  Survey, 
  for 
  the 
  following 
  notes 
  on 
  the 
  thin 
  sections 
  : 
  " 
  The 
  

   sections 
  consist 
  mainly 
  of 
  reddish 
  and 
  yellowish 
  brown 
  trans- 
  

   parent 
  amorphous 
  substance, 
  apparently 
  the 
  original 
  material, 
  

   this 
  is 
  traversed 
  in 
  all 
  directions 
  by 
  cracks 
  from 
  which 
  there 
  

   has 
  proceeded 
  a 
  decomposition 
  producing 
  a 
  reddish 
  brown 
  

   opaque 
  ochreous 
  matter 
  which 
  fills 
  the 
  cracks 
  and 
  replaces 
  the 
  

   original 
  material 
  so 
  that 
  in 
  certain 
  spots 
  there 
  is 
  now 
  merely 
  

   a 
  network 
  of 
  the 
  two 
  substances. 
  In 
  each 
  section 
  there 
  are 
  two 
  

   parallel 
  bands 
  of 
  secondary 
  minerals 
  nothing 
  corresponding 
  to 
  

   which 
  was 
  detected 
  in 
  the 
  chips 
  before 
  the 
  sections 
  were 
  made. 
  

   These 
  bands 
  consist 
  chiefly 
  of 
  two 
  colorless 
  minerals, 
  the 
  more 
  

   abundant 
  occurring 
  in 
  irregular 
  grains 
  closely 
  resembling 
  calcite 
  

   in 
  strength 
  of 
  refraction 
  and 
  double 
  refraction 
  ; 
  the 
  other 
  occurs 
  

   in 
  rounded 
  grains 
  and 
  is 
  probably 
  sphene. 
  In 
  addition 
  to 
  the 
  two 
  

   colorless 
  minerals 
  in 
  these 
  bands, 
  there 
  also 
  appear 
  two 
  brownish 
  

   substances, 
  one 
  of 
  which 
  has 
  distinct 
  prisms 
  without 
  terminal 
  

   planes, 
  shows 
  strong 
  pleochroism 
  and 
  its 
  absorption 
  parallel 
  to 
  

   the 
  vertical 
  axis 
  is 
  so 
  strong 
  as 
  to 
  make 
  it 
  opaque, 
  while 
  at 
  

   right 
  angles 
  to 
  this 
  axis 
  it 
  is 
  yellow-brown. 
  More 
  abundant 
  

   than 
  this 
  prismatic 
  mineral 
  is 
  one 
  occurring 
  in 
  apparent 
  flakes 
  

  

  * 
  Molecular 
  weight 
  =308. 
  

  

  f 
  Molecular 
  weight=312. 
  

  

  