﻿116 
  F. 
  ^¥. 
  Clarke— 
  Constitution 
  of 
  Tourmaline. 
  

  

  Here 
  the 
  divergence 
  between 
  the 
  composition 
  as 
  found 
  and 
  as 
  

   calculated 
  is 
  evidently 
  due 
  to 
  the 
  low 
  determinations 
  of 
  boric 
  

   acid 
  in 
  the 
  analyses. 
  Still, 
  the 
  comparison 
  is 
  close. 
  

  

  Between 
  the 
  magnesium 
  tourmalines 
  and 
  the 
  iron 
  tourma- 
  

   lines 
  the 
  closest 
  analogy 
  exists, 
  and 
  the 
  identity 
  of 
  type 
  is 
  abso- 
  

   lute. 
  Taking, 
  except 
  when 
  otherwise 
  specified, 
  the 
  analyses 
  

   by 
  Riggs, 
  all 
  the 
  iron 
  tourmalines 
  reduce 
  to 
  mixtures 
  of 
  the 
  

   following 
  isomorphous 
  molecules 
  : 
  

  

  A. 
  Al,(SiOJ,(BOJ,.B03(A10H).Fe,H,, 
  ) 
  

  

  B. 
  Al,(SiOJ,(BOJ,.B03Ca.Fe,H,, 
  f 
  

  

  C. 
  Al^(SiO 
  J^(B0J.^ 
  . 
  B03NaH 
  . 
  Al3NaH,, 
  

  

  D. 
  Al,(SiOJ,(BO;), 
  . 
  B03NaH 
  . 
  Al3Na,H, 
  

  

  E. 
  Al,(SiOJ,(BO 
  J, 
  . 
  B03NaU 
  . 
  Al3Na3. 
  

  

  Molecules 
  C, 
  D, 
  and 
  E 
  are 
  evidently 
  identical, 
  except 
  in 
  the 
  

   varying 
  replacements 
  of 
  sodium 
  by 
  hydrogen. 
  A 
  and 
  B 
  are 
  

   similarly 
  alike, 
  so 
  that 
  actually 
  only 
  two 
  fundamental 
  com- 
  

   pounds 
  are 
  assumed. 
  From 
  the 
  commoner 
  iron 
  tourmalines 
  

   lime 
  is 
  practically, 
  if 
  not 
  quite 
  absent 
  ; 
  and 
  these 
  may 
  be 
  inter- 
  

   preted 
  very 
  nearly 
  as 
  mixtures 
  of 
  A 
  and 
  C, 
  such 
  as 
  AgC^, 
  A^C^, 
  

   etc. 
  If 
  we 
  take 
  the 
  minute 
  quantities 
  of 
  lime 
  into 
  account, 
  

   the 
  black 
  tourmalines 
  from 
  Brazil 
  and 
  from 
  Stony 
  Point, 
  N. 
  C, 
  

   correspond 
  to 
  A,3B2C9 
  ; 
  that 
  from 
  Auburn, 
  Me., 
  to 
  Ag^B^C^, 
  ; 
  

   and 
  that 
  from 
  Paris, 
  Me., 
  to 
  AjoB^Cg. 
  It 
  will 
  be 
  noticed 
  that 
  

   the 
  molecule 
  A 
  is 
  in 
  excess 
  of 
  the 
  other 
  two 
  ; 
  a 
  condition 
  

   which 
  fits 
  the 
  analyses, 
  but 
  which 
  is 
  incompatible 
  with 
  the 
  

   formula 
  proposed 
  by 
  Penfield 
  and 
  Foote. 
  To 
  satisfy 
  the 
  latter 
  

   the 
  number 
  of 
  A 
  molecules 
  should 
  be 
  exactly 
  equal 
  to 
  B-f 
  C, 
  

   giving 
  the 
  ratio 
  '^\}d^^ 
  or 
  SigOgij^. 
  The 
  analyses 
  in 
  question 
  

   are 
  as 
  follows 
  : 
  

  

  Brazil. 
  Stony 
  Point. 
  Auburn. 
  Paris. 
  

  

  SiO, 
  34-63 
  35-56 
  34-99 
  35-03 
  

  

  B^Og.-.- 
  9-63 
  10-40 
  9-63 
  9-02 
  

  

  TiO, 
  ) 
  -55 
  

  

  A1„0„ 
  \ 
  32-70 
  33-38 
  33*96 
  34-44 
  

  

  Fe^O, 
  ) 
  _ 
  -31 
  .... 
  .... 
  1-13 
  

  

  FeO 
  ) 
  13-69 
  8-49 
  14-23 
  12-10 
  

  

  MnO 
  V 
  ._ 
  -12 
  -04 
  -06 
  '08 
  

  

  MgO 
  ) 
  2-13 
  5-44 
  1-01 
  1-81 
  

  

  CaO 
  -- 
  -33 
  -53 
  -15 
  -24 
  

  

  Li,0 
  ) 
  -08 
  trace 
  -07 
  

  

  NaO.^ 
  - 
  2-11 
  2-16 
  2-01 
  2-03 
  

  

  K^O 
  ) 
  -24 
  -24 
  -34 
  '25 
  

  

  HO) 
  3-49 
  3-63 
  3-62 
  3*69 
  

  

  f' 
  \ 
  ._-_ 
  -06 
  

  

  99-52 
  100-42 
  lOO'OO 
  99-89 
  

  

  