﻿F. 
  W. 
  ClarTie 
  — 
  Constitution 
  of 
  Tourmaline. 
  Ill 
  

  

  Akt. 
  XI. 
  — 
  The 
  Constitution 
  of 
  Tourmaline 
  \ 
  bj 
  F. 
  W. 
  

  

  Claeke. 
  

  

  Some 
  years 
  ago, 
  in 
  an 
  extended 
  paper 
  upon 
  the 
  constitution 
  

   ■of 
  the 
  silicates,^ 
  I 
  proposed 
  a 
  formula 
  for 
  tourmaline 
  which 
  

   seemed 
  to 
  satisfy 
  all 
  known 
  conditions. 
  Recently, 
  in 
  the 
  

   February 
  number 
  of 
  this 
  Journal, 
  Penfield 
  and 
  Footef 
  have 
  

   offered 
  still 
  another 
  interpretation 
  of 
  the 
  analyses, 
  and 
  support 
  

   their 
  views 
  with 
  a 
  considerable 
  weight 
  of 
  argument. 
  The 
  

   appearance 
  of 
  their 
  paper 
  has 
  led 
  me 
  to 
  rescrutinize 
  the 
  evi- 
  

   dence 
  more 
  in 
  detail 
  than 
  previously 
  ; 
  and 
  the 
  result 
  has 
  been 
  

   to 
  modify 
  my 
  formulae 
  in 
  some 
  particulars, 
  while 
  retaining 
  

   them 
  in 
  their 
  general 
  form. 
  

  

  According 
  to 
  Penfield 
  and 
  Foote 
  all 
  tourmaline 
  may 
  be 
  rep- 
  

   resented 
  as 
  salts 
  of 
  the 
  alumino-borosilicic 
  acid 
  Hj^AlgB.Si^O^,, 
  

   in 
  which 
  two 
  hydroxyls 
  are 
  permanently 
  linked 
  to 
  boron, 
  leav- 
  

   ing 
  an 
  available 
  valency 
  or 
  basicity 
  of 
  nine. 
  In 
  my 
  formulae 
  

   all 
  tourmalines 
  are 
  derived 
  from 
  the 
  similar 
  acid 
  Hi^AIgEgSigOgi, 
  

   with 
  all 
  of 
  the 
  hydrogen 
  atoms 
  replaceable 
  by 
  bases.' 
  Upon 
  

   bringing 
  the 
  two 
  acids 
  to 
  the 
  common 
  basis 
  of 
  six 
  silicon 
  

   atoms, 
  they 
  compare 
  as 
  follows 
  : 
  

  

  Penfield 
  and 
  Foote 
  _ 
  . 
  H^^^^Al^^EgSi^g,^ 
  

  

  Clarke 
  _.. 
  H, 
  Al 
  HSi.O„, 
  

  

  Replacing 
  aluminum 
  by 
  hydrogen 
  in 
  order 
  to 
  show 
  the 
  ulti- 
  

   mate 
  acids, 
  these 
  expressions 
  become 
  

  

  Penfield 
  and 
  Foote 
  Hg^BgSiPg,^ 
  

  

  Clarke 
  H^A^iA/ 
  

  

  The 
  small 
  difference 
  between 
  the 
  empirical 
  formulae 
  is 
  thus 
  

   made 
  evident, 
  and 
  it 
  hardly 
  amounts 
  to 
  more 
  than 
  the 
  uncer- 
  

   tainties 
  in 
  the 
  analyses. 
  In 
  fact, 
  the 
  trustworthy 
  analyses 
  of 
  

   tourmaline 
  give 
  ratios 
  lying 
  between 
  and 
  beyond 
  both 
  extremes, 
  

   as 
  the 
  following 
  formulae, 
  computed 
  from 
  Riggs' 
  data, 
  show 
  : 
  

   In 
  these 
  expressions 
  fluorine 
  has 
  been 
  assumed 
  equivalent 
  to 
  

   hydroxy 
  1. 
  

  

  Pierrepont, 
  black 
  H28.87'^2.93^i6C>30.83 
  

  

  Paris, 
  - 
  ..,- 
  H3„.,3B_SiA.3. 
  

  

  Stony 
  Point, 
  " 
  H^B^S.^.e. 
  

  

  Auburn, 
  colorless 
  H^^.^^B^.^^Si^Og^.,, 
  

  

  Brazil, 
  red 
  _ 
  ^,,.,,K..^\fi,,.,, 
  

  

  Gouverneur, 
  brown 
  H.^.g^B^.^^Si^g^.,^ 
  

  

  Hamburgh, 
  " 
  H3„.,gBg.„,SiA... 
  

  

  -'•Bulletin 
  U. 
  S. 
  Geological 
  Survey, 
  No. 
  125, 
  1895. 
  

   f 
  This 
  Journal, 
  vol. 
  vii, 
  p. 
  97, 
  1899. 
  

  

  