﻿482 
  F. 
  W. 
  Clarke 
  — 
  Constitution 
  of 
  Mel 
  i 
  lite 
  and 
  Gehlenite. 
  

  

  These 
  analyses 
  correspond 
  to 
  the 
  following 
  formulae 
  : 
  

  

  1. 
  8Al,(SiO 
  i 
  ).Ca. 
  + 
  lAl,(Si0 
  4 
  ),Ca, 
  + 
  2Al 
  a 
  (Si0 
  4 
  ) 
  6 
  Ca 
  6 
  (A10,Ca) 
  6 
  . 
  

  

  2. 
  4Al,(SiO.).Oa. 
  + 
  lAl 
  t 
  (SiO,).Oa 
  b 
  + 
  4Al 
  ! 
  (Si0 
  4 
  ),Ca,(A10 
  ! 
  Ca) 
  6 
  . 
  

  

  3. 
  lAI 
  4 
  (Si0 
  4 
  ) 
  6 
  Ca 
  6 
  + 
  lAI,(Si0 
  4 
  ).Ca, 
  + 
  2Al 
  s 
  (Si0 
  1 
  ) 
  6 
  Ca 
  6 
  (A10 
  a 
  Ca)„. 
  

  

  4. 
  lAl 
  4 
  (SiO 
  4 
  ) 
  6 
  Ca 
  + 
  9Al,(SiO 
  4 
  ).Cta 
  i 
  +llAl,(SiOJ.0a 
  i 
  (AlO.Ca) 
  r 
  

  

  5. 
  lAl,(Si0 
  4 
  ) 
  6 
  Ca, 
  + 
  4Al 
  a 
  (Si0 
  4 
  ),Ca,(A10 
  3 
  Ca), 
  approximately. 
  

  

  6. 
  17Al 
  4 
  (Si0 
  4 
  )„Ca, 
  +16Al 
  4 
  (Si0 
  4 
  ) 
  e 
  Ca 
  4 
  Na 
  4 
  + 
  36Al,(Si0 
  4 
  ),Ca„ 
  

  

  + 
  25Al,(Si0 
  4 
  ),Ca 
  6 
  (A10,Ca)„. 
  

  

  To 
  these 
  formulae 
  the 
  following 
  calculated 
  analyses 
  corre- 
  

   spond 
  : 
  

  

  Calculated 
  analyses 
  of 
  gehlenite. 
  

  

  

  l 
  

  

  2 
  

  

  3 
  

  

  4 
  

  

  

  5 
  

  

  6 
  

  

  Si0 
  2 
  

  

  33-00 
  

  

  31-37 
  

  

  30-32 
  

  

  29-72 
  

  

  27 
  

  

  •03 
  

  

  33-51 
  

  

  AiA 
  

  

  23-37 
  

  

  24-70 
  

  

  23*62 
  

  

  22-06 
  

  

  27 
  

  

  •57 
  

  

  20*40 
  

  

  CaO 
  

  

  43-63 
  

  

  43-93 
  

  

  46-06 
  

  

  48-22 
  

  

  45 
  

  

  •40 
  

  

  44*13 
  

  

  Na 
  2 
  

  

  

  

  

  

  

  

  

  

  -- 
  

  

  -- 
  

  

  1-96 
  

  

  100-00 
  100-00 
  100-00 
  100-00 
  100-00 
  10000 
  

  

  The 
  agreement 
  between 
  the 
  reduced 
  and 
  the 
  calculated 
  

   analyses 
  is 
  satisfactory, 
  except 
  in 
  the 
  case 
  of 
  the 
  Mexican 
  

   mineral, 
  which 
  seems 
  to 
  have 
  a 
  small 
  excess 
  of 
  alumina. 
  

  

  It 
  has 
  now 
  been 
  shown 
  that 
  melilite 
  and 
  gehlenite 
  can 
  be 
  

   represented 
  as 
  mixed 
  crystals 
  of 
  a 
  few 
  compounds 
  of 
  precisely 
  

   similar 
  chemical 
  type. 
  Sarcolite 
  and 
  the 
  melilite 
  silicate 
  are 
  

   known 
  compounds; 
  the 
  basic 
  gehlenite 
  silicate 
  is 
  hypothetical, 
  

   and 
  not 
  yet 
  found 
  in 
  the 
  free 
  state. 
  So 
  far 
  the 
  argument 
  is 
  

   weak, 
  but 
  it 
  is 
  strengthened 
  by 
  other 
  evidence 
  of 
  the 
  most 
  

   valid 
  kind. 
  The 
  garnets 
  and 
  prehnite 
  have, 
  as 
  we 
  have 
  seen, 
  

   the 
  same 
  type 
  of 
  structure, 
  and 
  several 
  other 
  lime-alumina 
  sili- 
  

   cates 
  can 
  be 
  compared 
  with 
  these. 
  The 
  following 
  formulae 
  

   may 
  be 
  taken 
  as 
  illustrative 
  of 
  this 
  fact 
  : 
  

  

  / 
  Si0 
  4 
  = 
  Al, 
  = 
  Si0 
  4 
  \ 
  

  

  Al 
  — 
  Si0 
  4 
  = 
  Ca 
  3 
  = 
  SiO, 
  — 
  Al 
  

  

  \ 
  Si0 
  4 
  - 
  Ca 
  - 
  Si0 
  4 
  / 
  

  

  II 
  II 
  

  

  AlOH 
  AlOH 
  

  

  Al 
  

  

  

  /Si0 
  4 
  EE 
  

  

  = 
  A1 
  S 
  : 
  

  

  E 
  SiO. 
  

  

  \ 
  

  

  A] 
  

  

  — 
  SiO 
  - 
  

  

  4 
  

  

  ;AI,= 
  

  

  = 
  SiO, 
  

  

  4 
  

  

  — 
  Al 
  

  

  

  \ 
  SiO, 
  = 
  

  

  = 
  Ca 
  3 
  = 
  

  

  = 
  Si0 
  4 
  

  

  4 
  

  

  / 
  

  

  

  Anorthite 
  

  

  

  Ai 
  

  

  /Si0 
  4 
  EE 
  

   l-Sl0 
  4 
  EE 
  

  

  :Ca 
  s 
  

   ECa 
  s 
  ; 
  

  

  = 
  Si0 
  4 
  

   = 
  Si0 
  4 
  

  

  \ 
  

  

  — 
  Al 
  

  

  

  \ 
  Si0 
  4 
  - 
  

  

  II 
  

   AlOH 
  

  

  - 
  Ca 
  

  

  -Si0 
  4 
  / 
  

  

  II 
  

  

  AlOH 
  

  

  

  Vesuviar, 
  

  

  ite 
  

  

  

  

  Zoisite 
  

  

  

  

  

  Si0 
  4 
  

  

  = 
  A1,= 
  

  

  :Si0 
  4 
  

  

  \ 
  

  

  

  Si0 
  4 
  

  

  = 
  A1,= 
  

  

  Si0 
  4 
  

  

  

  

  Al 
  

  

  Si0 
  4 
  

  

  1 
  

  

  = 
  Oa,= 
  

  

  :Si0 
  4 
  

  

  4 
  

  

  / 
  

  

  

  I 
  

   Ca 
  

  

  - 
  O 
  - 
  

  

  Meionite 
  

  

  Ca 
  

  

  

  

  