﻿L. 
  V. 
  Pirsson 
  — 
  Gmelinite 
  from 
  Nova 
  Scotia. 
  63 
  

  

  the 
  first 
  a 
  hydrated 
  albite 
  molecule, 
  the 
  second 
  a 
  hydrated 
  soda 
  

   anorthite. 
  If, 
  according 
  to 
  this, 
  we 
  deduce 
  the 
  composition 
  

   indicated 
  by 
  the 
  analyses 
  of 
  the 
  three 
  gmelinites, 
  replacing 
  

   soda 
  by 
  lime 
  to 
  the 
  extent 
  observed, 
  we 
  have 
  

  

  Two 
  Islands 
  =to 
  + 
  y 
  in 
  which 
  Na 
  : 
  Ca 
  

   Bergen 
  Hill 
  =3a3 
  + 
  y 
  " 
  Na 
  : 
  Ca 
  

   Five 
  Islands 
  =4x-\-y 
  " 
  Na 
  : 
  Ca 
  

  

  : 
  2 
  : 
  3 
  

   : 
  3-2: 
  1 
  

   : 
  8 
  : 
  1 
  

  

  The 
  theoretical 
  composition 
  for 
  these 
  formulas 
  is 
  given, 
  for 
  

   convenience, 
  in 
  the 
  table 
  after 
  each 
  analysis. 
  The 
  very 
  close 
  

   agreement 
  of 
  the 
  theory, 
  calculated 
  for 
  these 
  simple 
  relations, 
  

   with 
  the 
  analyses 
  themselves 
  is 
  very 
  striking 
  and 
  a 
  strong 
  

   proof 
  of 
  the 
  correctness 
  of 
  Streng's 
  theory. 
  In 
  chemical 
  com- 
  

   position 
  we 
  may 
  consider 
  typical 
  gmelinite 
  as 
  a 
  soda 
  chaba- 
  

   zite, 
  whose 
  relation 
  to 
  the 
  normal 
  lime 
  chabazite 
  is 
  the 
  same 
  as 
  

   that 
  for 
  instance 
  of 
  lithiophilite 
  to 
  triphylite. 
  

  

  Conclusion. 
  — 
  In 
  considering 
  the 
  bearing 
  of 
  the 
  foregoing 
  

   facts 
  upon 
  the 
  identity 
  of 
  this 
  mineral 
  with 
  chabazite 
  there 
  is 
  

   an 
  apparent 
  discordance. 
  The 
  result 
  of 
  the 
  crystallographic 
  

   work, 
  points 
  to 
  a 
  distinct 
  difference 
  in 
  axial 
  ratios 
  and 
  there 
  is 
  

   also 
  a 
  different 
  habit 
  and 
  cleavage. 
  On 
  the 
  other 
  hand 
  the 
  

   twinning 
  and 
  the 
  chemical 
  constitution, 
  both 
  following 
  that 
  of 
  

   chabazite 
  present 
  the 
  strongest 
  possible 
  arguments 
  for 
  the 
  

   identity 
  of 
  the 
  species. 
  To 
  explain 
  these 
  apparent 
  discrepan- 
  

   cies 
  the 
  following 
  hypothesis 
  is 
  offered. 
  The 
  analyses 
  of 
  

   chabazite 
  and 
  gmelinite, 
  made 
  by 
  various 
  chemists, 
  show 
  that 
  

   soda 
  and 
  lime 
  may 
  replace 
  each 
  other 
  to 
  any 
  extent, 
  but 
  that 
  

   in 
  gmelinite 
  the 
  soda 
  is 
  in 
  excess, 
  while 
  in 
  chabazite 
  the 
  reverse 
  

   is 
  true. 
  If 
  we 
  consider 
  then 
  that 
  the 
  effect 
  of 
  the 
  soda 
  is 
  to 
  

   lengthen 
  somewhat 
  the 
  vertical 
  axis, 
  the 
  difference 
  in 
  angles 
  

   and 
  ratios 
  would 
  be 
  accounted 
  for 
  and 
  we 
  might 
  expect 
  it 
  to 
  

   change 
  also 
  the 
  habit 
  and 
  cleavage. 
  While 
  this 
  cannot 
  be 
  

   considered 
  otherwise 
  than 
  a 
  hypothesis, 
  the 
  fact 
  that 
  in 
  

   the 
  Five 
  Island 
  material 
  under 
  examination 
  these 
  differences 
  

   are 
  greater 
  than 
  noted 
  by 
  any 
  former 
  observer, 
  while 
  at 
  the 
  

   same 
  time 
  the 
  percentage 
  of 
  soda 
  is 
  also 
  greater, 
  points 
  dis- 
  

   tinctly 
  towards 
  it. 
  According 
  to 
  this 
  view 
  gmelinite 
  would 
  

   bear 
  much 
  the 
  same 
  relation 
  to 
  chabazite 
  that 
  enstatite 
  does 
  to 
  

   hypersthene, 
  whether 
  it 
  should 
  be 
  considered 
  a 
  distinct 
  species 
  

   would 
  be 
  largely 
  a 
  matter 
  of 
  choice 
  or 
  convenience. 
  

  

  In 
  closing 
  the 
  author 
  desires 
  to 
  express 
  his 
  thanks 
  for 
  the 
  

   liberal 
  use 
  of 
  valuable 
  material 
  to 
  Professor 
  G-. 
  J. 
  Brush 
  and 
  

   to 
  Professor 
  S. 
  L. 
  Pentield, 
  to 
  the 
  latter 
  also 
  for 
  valuable 
  

   advice 
  during 
  the 
  progress 
  of 
  this 
  examination. 
  

  

  Mineralogical 
  Laboratory, 
  Sheffield 
  Scientific 
  School, 
  

   New 
  Haven, 
  Feb., 
  1891. 
  

  

  Am. 
  Jour. 
  Sci 
  — 
  Third 
  Series, 
  Yol. 
  XLII, 
  No. 
  247.— 
  July, 
  1891. 
  

  

  