﻿58 
  L. 
  V. 
  Pirsson 
  — 
  G?nelinite 
  from 
  Nova 
  Scotia. 
  

  

  The 
  following 
  table 
  shows 
  the 
  forms 
  which 
  have 
  been 
  

   observed 
  on 
  these 
  crystals, 
  several 
  of 
  which 
  are 
  new. 
  In 
  the 
  

   first 
  column 
  the 
  symbols 
  are 
  those 
  of 
  gmelinite 
  as 
  a 
  distinct 
  

   species, 
  in 
  the 
  second 
  the 
  same 
  are 
  referred 
  to 
  the 
  axes 
  of 
  

   chabazite. 
  

  

  As 
  gmelinite. 
  

  

  As 
  chabazite. 
  

  

  As 
  gmelinite. 
  

  

  As 
  chabazite. 
  

  

  c, 
  0, 
  0001 
  

  

  0. 
  0001 
  

  

  r, 
  R, 
  1011 
  

  

  f, 
  2023 
  

  

  m, 
  I, 
  1010 
  

  

  I, 
  1010 
  

  

  p, 
  -1, 
  0111 
  

  

  -|, 
  0223 
  

  

  a, 
  i-2, 
  1120 
  

  

  i-2, 
  1120 
  

  

  q, 
  f, 
  3032 
  

  

  R, 
  1011 
  

  

  I, 
  i-\, 
  5270 
  

  

  i"4, 
  5270 
  

  

  <£, 
  f 
  7 
  , 
  4.377 
  

  

  - 
  2 
  \ 
  7 
  , 
  8 
  6 
  14 
  21 
  

  

  Of 
  these 
  forms 
  c, 
  a, 
  / 
  and 
  q 
  are 
  rare, 
  the 
  others 
  occur 
  on 
  all 
  

   crystals, 
  almost 
  without 
  exception, 
  from 
  American 
  localities. 
  

   The 
  basal 
  plane 
  c 
  occurs 
  only 
  on 
  a 
  few 
  crystals 
  from 
  Two 
  

   Islands 
  and 
  on 
  a 
  number 
  of 
  those 
  from 
  Bergen 
  Hill. 
  As 
  

   noted 
  by 
  others, 
  the 
  face 
  p 
  is 
  generally 
  characterized 
  by 
  the 
  

   vicinal 
  development 
  of 
  a 
  pair 
  of 
  low 
  scalenohedrons. 
  The 
  

   prism 
  m 
  is 
  not 
  generally 
  striated 
  in 
  a 
  horizontal 
  direction, 
  as 
  

   observed 
  on 
  European 
  forms. 
  The 
  scalenohedron 
  <p 
  is 
  invaria- 
  

   bly 
  striated, 
  oscillating 
  with 
  both 
  the 
  plus 
  and 
  minus 
  rhombo 
  

   hedrons 
  and 
  in 
  some 
  cases, 
  possibly, 
  with 
  a 
  pyramid 
  of 
  the 
  

   second 
  order 
  and 
  a 
  minus 
  form 
  of 
  the 
  same 
  scalenohedron. 
  

   Many 
  crystals 
  show 
  on 
  the 
  goniometer, 
  by 
  revolving 
  in 
  the 
  

   zone 
  r-p, 
  a 
  continuous 
  band 
  of 
  light 
  with 
  the 
  signals 
  of 
  these 
  

   faces 
  standing 
  out. 
  The 
  scalenohedron 
  mentioned 
  is, 
  however, 
  

   most 
  prominent. 
  The 
  presence 
  of 
  this 
  striated 
  scalenohedron 
  

   <p 
  is 
  the 
  most 
  characteristic 
  feature 
  of 
  the 
  American 
  forms, 
  it 
  is 
  

   almost 
  never 
  lacking 
  on 
  any 
  of 
  the 
  large 
  number 
  of 
  specimens 
  

   examined. 
  A 
  common 
  appearance 
  of 
  one 
  corner 
  of 
  the 
  Pin- 
  

   nacle 
  Island 
  crystals, 
  where 
  it 
  oscillates 
  with 
  the 
  rhombohedrons, 
  

   is 
  shown 
  in 
  fig. 
  3. 
  

  

  While 
  in 
  general 
  the 
  crystal 
  planes 
  gave 
  poor 
  reflections 
  of 
  

   the 
  signal, 
  a 
  number 
  from 
  Pinnacle 
  Island 
  were 
  well 
  suited, 
  by 
  

   the 
  brilliancy 
  and 
  luster 
  of 
  the 
  unit 
  rhombohedron, 
  for 
  measur- 
  

   ing 
  the 
  polar 
  angle 
  r 
  ^r. 
  This 
  was 
  done 
  on 
  a 
  series 
  of 
  ten 
  

   carefully 
  selected 
  crystals 
  and 
  the 
  results 
  are 
  given 
  in 
  the 
  fol- 
  

   lowing 
  table. 
  Each 
  measurement 
  is 
  the 
  mean 
  of 
  five 
  deter- 
  

   minations 
  and 
  the 
  greatest 
  variation 
  between 
  the 
  mean 
  and 
  any 
  

   one 
  determination 
  is 
  given 
  in 
  the 
  second 
  column. 
  

  

  0' 
  

  

  42" 
  

  

  0° 
  

  

  0' 
  

  

  48" 
  

  

  68° 
  

  

  8' 
  

  

  0" 
  

  

  0° 
  

  

  0' 
  

  

  

  

  10 
  

  

  24 
  

  

  

  

  

  

  36 
  

  

  67 
  

  

  56 
  

  

  54 
  

  

  

  

  

  

  54 
  

  

  6 
  

  

  12 
  

  

  

  

  

  

  18 
  

  

  68 
  

  

  77 
  

  

  24 
  

  

  

  

  

  

  36 
  

  

  3 
  

  

  40 
  

  

  

  

  

  

  40 
  

  

  68 
  

  

  

  

  18 
  

  

  

  

  1 
  

  

  12 
  

  

  4 
  

  

  18 
  

  

  

  

  

  

  18 
  

  

  68 
  

  

  

  

  45 
  

  

  

  

  

  

  55 
  

  

  Average 
  68 
  3 
  51 
  

  

  The 
  table 
  shows 
  the 
  degree 
  of 
  accuracy 
  with 
  which 
  the 
  

   angle 
  could 
  be 
  measured. 
  Of 
  the 
  above, 
  that 
  which 
  gave 
  

   68° 
  08 
  / 
  was 
  selected 
  as 
  a 
  fundamental. 
  The 
  reflections 
  of 
  the 
  

  

  