﻿114 
  F. 
  W. 
  Clarke 
  — 
  Constitution 
  of 
  Tourmaline. 
  

  

  The 
  result 
  is 
  evidently 
  satisfactory. 
  In 
  dealing 
  with 
  titanium 
  

   I 
  have 
  followed 
  Penfield, 
  regarding 
  it 
  as 
  really 
  Ti^Og 
  and 
  

   equivalent 
  to 
  alumina. 
  The 
  fluorine 
  is 
  treated 
  as 
  replacing 
  

   hydroxjl 
  and 
  is, 
  therefore, 
  united 
  with 
  the 
  water. 
  It 
  is 
  pos- 
  

   sible, 
  however, 
  that 
  fluorine 
  may 
  sometimes 
  replace 
  the 
  group 
  

   BO2, 
  an 
  equivalency 
  which 
  is 
  strongly 
  indicated 
  in 
  the 
  cap- 
  

   pelenite 
  group 
  of 
  minerals. 
  

  

  The 
  brown 
  tourmaline 
  from 
  Gouverneur, 
  X. 
  Y., 
  as 
  analyzed 
  

   by 
  Riggs, 
  also 
  reduces 
  to 
  a 
  similar 
  mixture 
  of 
  molecules, 
  and 
  

   its 
  composition 
  may 
  be 
  written 
  thus 
  : 
  

  

  5. 
  Al,(SiOJ,(BOJ,.B03Ca.Mg,H,, 
  

   3. 
  Al,(SiOJ,(BOJ,.B03Mg.Mg,H, 
  

   2. 
  Al,(SiO 
  J,(BO 
  J, 
  . 
  B03NaH 
  . 
  Al,Na,H, 
  ; 
  

  

  and 
  the 
  comparison 
  between 
  analysis 
  and 
  theory 
  is 
  as 
  follows 
  : 
  

  

  Found. 
  Reduced. 
  Calculated. 
  

  

  SiO, 
  .37-39 
  3'7-54 
  37-32 
  

  

  B2O3 
  ._ 
  10-73 
  10-76 
  10-88 
  

  

  AI2O3 
  __- 
  27-79) 
  28-72 
  28-53 
  

  

  FeA 
  -10 
  

  

  TiO, 
  1-19 
  

  

  FeO 
  -64 
  ) 
  

  

  MgO 
  14-09 
  i" 
  14-51 
  14-52 
  

  

  CaO 
  2-78 
  2-79 
  2*90 
  

  

  Na^O 
  1-72) 
  1-83 
  1-93 
  

  

  K,0 
  -16 
  \ 
  

  

  H^O-- 
  _ 
  3-83 
  3-85 
  3-92 
  

  

  100-42 
  100-00 
  100-00 
  

  

  By 
  consolidating 
  lime 
  with 
  magnesia 
  the 
  expressions 
  for 
  both 
  

   tourmalines 
  might 
  be 
  simplified 
  ; 
  but 
  in 
  other 
  cases 
  this 
  would 
  

   not 
  be 
  warranted. 
  In 
  some 
  tourmalines 
  calcium 
  seems 
  rather 
  

   to 
  replace 
  sodium, 
  or 
  else 
  the 
  group 
  I^aH 
  ; 
  a 
  probability 
  which 
  

   will 
  appear 
  later. 
  

  

  In 
  these 
  two 
  tourmalines 
  the 
  theoretical 
  silicon-oxygen 
  ratio 
  

   SigOg, 
  is 
  assumed, 
  in 
  accordance 
  with 
  my 
  original 
  formula. 
  We 
  

   may 
  now 
  consider 
  the 
  cases 
  in 
  which 
  that 
  ratio 
  is 
  exceeded, 
  

   with 
  more 
  or 
  less 
  approach 
  to 
  the 
  formula 
  proposed 
  by 
  Penfield 
  

   and 
  Foote. 
  This 
  condition 
  is 
  easily 
  satisfied 
  by 
  regarding 
  one 
  

   of 
  the 
  component 
  salts 
  of 
  tourmaline 
  as 
  slightly 
  basic 
  ; 
  contain- 
  

   ing 
  the 
  bivalent 
  group 
  =Al--0 
  — 
  H 
  or 
  =A1 
  — 
  F 
  as 
  an 
  essential 
  

   factor. 
  With 
  this 
  assumption, 
  which 
  recognizes 
  the 
  equiva- 
  

   lency 
  of 
  hydroxyl 
  and 
  fluorine, 
  the 
  analyses 
  reduce 
  to 
  the 
  

   general 
  type 
  indicated 
  in 
  the 
  two 
  preceding 
  examples. 
  For 
  

   instance, 
  the 
  white 
  tourmaline 
  from 
  DeKalb, 
  N. 
  Y., 
  has 
  the 
  

   following 
  composition 
  : 
  

  

  