﻿94 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  They 
  are 
  expressed, 
  on 
  the 
  supposition 
  stated 
  above, 
  in 
  the 
  

   formula, 
  2 
  Ca 
  Al 
  Si 
  2 
  8 
  ) 
  or, 
  2 
  Mol. 
  Anorthite 
  ) 
  

  

  Na 
  2 
  Al 
  Si 
  6 
  16 
  ) 
  1 
  Mol. 
  Albite 
  f 
  

  

  In 
  A, 
  if 
  Na 
  : 
  Ca 
  = 
  1 
  : 
  1.5, 
  then 
  Al 
  : 
  Si 
  = 
  1 
  : 
  3, 
  instead 
  of 
  1 
  : 
  3.5, 
  

   as 
  obtained 
  by 
  the 
  analysis 
  ; 
  and 
  in 
  B, 
  if 
  Na 
  : 
  Ca 
  = 
  1 
  : 
  1, 
  then 
  

   Al 
  : 
  Si 
  = 
  1 
  : 
  1.33, 
  instead 
  of 
  1 
  : 
  1.52. 
  

  

  Much 
  of 
  the 
  ferric, 
  and 
  probably 
  all 
  of 
  the 
  ferrous, 
  oxide, 
  

   exists 
  in 
  both 
  these 
  varieties 
  of 
  labradorite 
  as 
  magnetite 
  and 
  

   menaccanite, 
  and 
  if 
  we 
  knew 
  with 
  exactness 
  the 
  composition 
  

   of 
  the 
  latter 
  mineral 
  as 
  it 
  exists 
  in 
  the 
  minerals, 
  might 
  with 
  

   advantage 
  be 
  excluded 
  from 
  the 
  computation 
  of 
  the 
  formulae. 
  

   The 
  silica 
  in 
  both 
  analyses 
  exceeds 
  that 
  which 
  the 
  formulae 
  

   require, 
  but 
  this 
  excess, 
  as 
  the 
  microscopic 
  examination 
  shows, 
  

   is 
  not 
  due 
  to 
  combined 
  silica, 
  but 
  to 
  free 
  quartz. 
  And 
  it 
  is 
  

   important 
  to 
  note, 
  that 
  while 
  quartzites 
  are 
  not 
  included 
  in 
  this 
  

   suite 
  of 
  Adirondacks 
  rocks 
  and 
  were 
  not 
  encountered 
  by 
  the 
  

   writer 
  in 
  the 
  limited 
  area 
  from 
  which 
  the 
  collections 
  were 
  made, 
  

   at 
  the 
  same 
  time, 
  in 
  every 
  microscopic 
  section 
  examined 
  and 
  

   every 
  analysis 
  which 
  has 
  been 
  performed, 
  a 
  notable 
  amount 
  of 
  

   uncombined 
  silicic 
  acid 
  is 
  present. 
  In 
  some 
  cases, 
  it 
  is 
  true, 
  

   veins 
  filled 
  with 
  quartz 
  and 
  amethyst 
  crystals 
  have 
  been 
  encoun- 
  

   tered, 
  but 
  these 
  appear 
  to 
  have 
  been 
  formed 
  by 
  infiltration 
  and 
  

   deposition. 
  

  

  If 
  the 
  density 
  of 
  Albite 
  be 
  2.62, 
  its 
  atomic 
  volume 
  is 
  400.4. 
  

   Moreover, 
  assuming 
  that 
  homoemorphous 
  species 
  have 
  similar 
  

   atomic 
  volumes, 
  the 
  formula 
  of 
  anorthite 
  will 
  be 
  Ca 
  2 
  Al 
  2 
  Si 
  4 
  O 
  16 
  , 
  

   and 
  its 
  atomic 
  volume, 
  with 
  density 
  2.76, 
  is 
  403.8. 
  The 
  relation- 
  

   ship 
  between 
  the 
  two 
  varieties 
  of 
  labradorite 
  would 
  then 
  be 
  : 
  — 
  

  

  Density. 
  Atomic 
  Vol. 
  

  

  | 
  Ca 
  2 
  Al 
  2 
  Si 
  4 
  16 
  | 
  272 
  4(X) 
  2 
  

  

  Q16 
  

  

  Ca 
  2 
  

  

  Al 
  2 
  

  

  Si 
  4 
  

  

  ISTa 
  2 
  

  

  Al 
  

  

  Si 
  6 
  

  

  Ca 
  2 
  

  

  Al 
  2 
  

  

  Si 
  4 
  

  

  ISTa 
  2 
  

  

  Al 
  

  

  Si 
  6 
  

  

  16 
  ) 
  

  

  u 
  } 
  2.70 
  400.6 
  

  

  B 
  ISTa 
  2 
  Al 
  Si 
  6 
  16 
  i 
  

  

  In 
  these 
  two 
  closely 
  related 
  minerals, 
  the 
  densities 
  as 
  deter- 
  

   mined 
  by 
  careful 
  trial, 
  vary 
  directly 
  with 
  the 
  atomic 
  weights 
  

   and 
  the 
  atomic 
  volumes 
  are 
  nearly 
  equal. 
  Upon 
  the 
  supposi- 
  

   tion 
  that 
  the 
  atomic 
  volumes 
  of 
  homoemorphous 
  species 
  are 
  

   identical, 
  and 
  that, 
  as 
  appears 
  to 
  be 
  the 
  case 
  with 
  the 
  two 
  lab- 
  

   radorites 
  and 
  the 
  albite, 
  the 
  atomic 
  volume 
  for 
  the 
  group 
  of 
  

  

  