﻿MAY 
  19, 
  1922 
  SHANNON 
  AND 
  WHERRY: 
  WHITE 
  CHLORlTES 
  241 
  

  

  As 
  to 
  occurrence 
  and 
  origin, 
  the 
  Pennsylvania 
  specimens 
  are 
  reported 
  

   by 
  Mr. 
  Gordon 
  to 
  have 
  been 
  formed 
  by 
  the 
  action 
  on 
  albite-pegma- 
  

   tite 
  of 
  magnesium-bearing 
  waters 
  derived 
  from 
  the 
  weathering 
  of 
  

   serpentine 
  and 
  jefferisite.^ 
  The 
  original 
  colerainite 
  had 
  a 
  similar 
  ori- 
  

   gin/' 
  The 
  sheridanite 
  occurs 
  in 
  granitic 
  rocks, 
  and 
  may 
  have 
  also 
  arisen 
  

   through 
  alteration 
  of 
  feldspar, 
  but 
  details 
  of 
  its 
  occurrence 
  are 
  not 
  

   known. 
  

  

  Both 
  Pennsylvania 
  minerals 
  are 
  rather 
  different 
  from 
  colerainite 
  in 
  

   composition, 
  but 
  the 
  first 
  one 
  agrees 
  closely 
  with 
  sheridanite 
  in 
  this 
  

   respect, 
  although 
  entirely 
  different 
  from 
  it 
  in 
  physical 
  properties. 
  It 
  

   is 
  not 
  possible 
  at 
  present 
  to 
  interpret 
  the 
  analyses 
  of 
  any 
  of 
  these 
  in 
  

   terms 
  of 
  end-minerals, 
  so 
  it 
  seems 
  best 
  to 
  class 
  them 
  all 
  simply 
  as 
  

   white 
  chlorites. 
  

  

  A 
  crystallographic 
  confirmation 
  of 
  the 
  identity 
  of 
  these 
  minerals 
  

   seemed 
  desirable, 
  but 
  the 
  Brinton's 
  Quarry 
  and 
  Nottingham 
  material 
  

   proved 
  to 
  be 
  too 
  dull 
  on 
  the 
  surface 
  to 
  give 
  definite 
  results. 
  Optical 
  

   examination 
  of 
  the 
  so-called 
  secondary 
  albite 
  from 
  Sylmar, 
  Pa.'^ 
  

   showed, 
  however, 
  that 
  it 
  is 
  of 
  similar 
  character 
  although 
  too 
  exten- 
  

   sively 
  altered 
  to 
  kaolinite 
  to 
  be 
  suitable 
  for 
  analysis. 
  It 
  occurs 
  in 
  

   rosettes 
  of 
  subparallel 
  crystal 
  plates 
  on 
  compact 
  albite 
  rock, 
  averaging 
  

   5 
  b}^ 
  1 
  mm. 
  in 
  size, 
  with 
  perfect 
  basal 
  cleavage 
  on 
  which 
  the 
  luster 
  is 
  

   bronzy. 
  These 
  were 
  found 
  to 
  give 
  hazy 
  light 
  nodes 
  as 
  a 
  number 
  of 
  

   places 
  in 
  each 
  zone 
  of 
  faces, 
  yielding 
  the 
  results 
  shown 
  in 
  table 
  2. 
  

  

  TABLE 
  2.— 
  Angles 
  of 
  White 
  Chlorite 
  from 
  Sylmar, 
  Pa. 
  

   Crystallization 
  perihexagonal 
  ; 
  c 
  = 
  3.3890 
  ± 
  .0050 
  

  

  The 
  identification 
  of 
  the 
  material 
  as 
  a 
  white 
  chlorite 
  is 
  thus 
  complete. 
  

  

  5 
  Proc. 
  Acad. 
  Nat. 
  Sci. 
  Phila. 
  1921 
  ': 
  169-192. 
  1921. 
  

   « 
  Trans. 
  Royal 
  Soc. 
  Canada 
  III, 
  12: 
  37-39. 
  1918. 
  

   ' 
  Amer. 
  Min. 
  3: 
  47. 
  1918. 
  

  

  