﻿certain 
  Micas, 
  Vermiculites 
  and 
  Chlorites. 
  243 
  

  

  The 
  analysis 
  of 
  protovermiculite 
  agrees 
  with 
  that 
  of 
  Konig 
  

   as 
  well 
  as 
  could 
  be 
  expected, 
  but 
  is 
  carried 
  out 
  somewhat 
  more 
  

   in 
  detail. 
  In 
  its 
  appearance 
  the 
  mineral 
  was 
  dark 
  brown, 
  broadly 
  

   foliated, 
  much 
  decomposed, 
  and 
  very 
  brittle. 
  Before 
  the 
  blow- 
  

   pipe 
  it 
  exfoliates 
  and 
  fuses 
  easily. 
  The 
  Henderson 
  County 
  

   mica 
  was 
  also 
  brown, 
  brittle 
  and 
  decomposed, 
  exfoliating 
  when 
  

   heated 
  and 
  fusing 
  at 
  the 
  edges. 
  Both 
  minerals 
  were 
  examined 
  

   optically 
  by 
  Mr. 
  Waldemar 
  Lindgren. 
  The 
  protovermiculite 
  

   he 
  describes 
  as 
  " 
  yellowish, 
  containing 
  in 
  arborescent 
  forms 
  

   between 
  the 
  plates 
  a 
  great 
  deal 
  of 
  a 
  deep 
  yellow 
  or 
  reddish 
  

   substance, 
  probably 
  hydroxide 
  of 
  iron. 
  Angle 
  of 
  optical 
  

   axes 
  larger 
  than 
  usual. 
  Slight 
  pleochroism 
  ; 
  thicker 
  plates 
  

   remain 
  light 
  between 
  crossed 
  nicols." 
  Of 
  the 
  Henderson 
  

   County 
  mica 
  he 
  says 
  — 
  "contains 
  no 
  titanium 
  mineral. 
  Con- 
  

   tains 
  a 
  few 
  grains 
  of 
  a 
  colorless, 
  strongly 
  double-refracting 
  

   mineral 
  of 
  uncertain 
  nature, 
  possibly 
  zircon. 
  Plates 
  nearly 
  

   dark 
  between 
  crossed 
  nicols. 
  Angle 
  of 
  optical 
  axes 
  small, 
  but 
  

   distinctly 
  observed." 
  In 
  the 
  material 
  selected 
  for 
  analysis 
  the 
  

   impurities 
  noted 
  by 
  Lindgren 
  were 
  so 
  far 
  as 
  possible 
  removed. 
  

  

  The 
  composition 
  of 
  each 
  mineral 
  reduces 
  quite 
  easily, 
  in 
  

   accordance 
  with 
  the 
  methods 
  followed 
  in 
  our 
  former 
  work, 
  to 
  

   a 
  mixture 
  of 
  simple 
  isomorphous 
  types. 
  The 
  only 
  uncertain- 
  

   ties 
  appear 
  to 
  be 
  in 
  connection 
  with 
  the 
  loosely 
  combined 
  

   water, 
  which 
  is 
  driven 
  off 
  below 
  300°. 
  In 
  the 
  Henderson 
  

   County 
  mica 
  we 
  have 
  the 
  molecules 
  

  

  /Si0 
  4 
  =MgK 
  /SiO=H 
  3 
  /SiO=MgH 
  /<K 
  M 
  

   Al— 
  SiO=MgH 
  Al— 
  Si0 
  4 
  =H 
  3 
  Fe— 
  SiO^MgH 
  Fe— 
  0^ 
  m 
  ^ 
  

   \ 
  Si0 
  4 
  =Al 
  \ 
  SiO=H 
  3 
  \ 
  SiO 
  =EFe 
  \ 
  Si0 
  4 
  =H 
  3 
  

  

  in 
  the 
  ratio 
  8 
  : 
  1 
  : 
  3 
  J 
  : 
  3. 
  The 
  loosely 
  combined 
  water 
  is 
  in 
  the 
  

   proper 
  amount 
  to 
  monohydrate 
  the 
  four 
  molecules 
  ; 
  but 
  its 
  

   actual 
  distribution 
  is 
  uncertain. 
  In 
  the 
  subjoined 
  table 
  mono- 
  

   hydration 
  is 
  provisionally 
  assumed. 
  In 
  the 
  protovermiculite 
  

   we 
  have 
  the 
  three 
  molecules 
  

  

  /SiO=H 
  3 
  /°->M^ 
  /( 
  SM<r 
  

  

  Al— 
  SiO=H 
  3 
  Al— 
  >M 
  S 
  Fe— 
  >M 
  ^ 
  

  

  \Si0 
  4 
  =H 
  3 
  \Si0 
  4 
  =H 
  3 
  \SiO=Al 
  

  

  each 
  plus 
  three 
  molecules 
  of 
  water, 
  in 
  the 
  ratio 
  14 
  : 
  6 
  : 
  9. 
  As 
  

   in 
  the 
  case 
  of 
  jeiferisite 
  and 
  kerrite, 
  the 
  three 
  molecules 
  of 
  

   loosely 
  combined 
  water 
  are 
  unlike 
  ; 
  two 
  being 
  given 
  off 
  over 
  

   sulphuric 
  acid, 
  and 
  the 
  third 
  retained 
  rather 
  more 
  tenaciously. 
  

   Reducing 
  the 
  original 
  analyses 
  to 
  100 
  per 
  cent, 
  uniting 
  all 
  

   similar 
  oxides 
  to 
  similar 
  type, 
  reckoning 
  FeO 
  as 
  MgO, 
  Ea 
  Q 
  

   as 
  K 
  2 
  0, 
  Ti0 
  2 
  as 
  Si0 
  2 
  , 
  etc., 
  we 
  get 
  the 
  following 
  comparison 
  

   between 
  observation 
  and 
  theory 
  : 
  

  

  