﻿242 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  10 
  

  

  MINERALOGY. 
  — 
  Crocidolite 
  from 
  eastern 
  Pennsylvania} 
  Edgar 
  

   T. 
  Wherry 
  and 
  Earl 
  V. 
  Shannon, 
  U. 
  S. 
  National 
  Museum. 
  

   The 
  occurrence 
  of 
  a 
  glaucamphibole 
  in 
  the 
  Highland 
  belt 
  of 
  pre- 
  

   Cambrian 
  rocks 
  of 
  eastern 
  Pennsylvania 
  was 
  noted 
  by 
  D'Invilliers 
  

   in 
  1883.- 
  He 
  classed 
  the 
  mineral 
  as 
  an 
  amphibole 
  on 
  the 
  basis 
  of 
  a 
  

   "rough 
  analysis" 
  by 
  State 
  Chemist 
  McCreath 
  made 
  on 
  "a 
  portion 
  of 
  

   the 
  mass 
  more 
  or 
  less 
  mixed 
  with 
  feldspar" 
  which 
  yielded, 
  when 
  the 
  

   meaningless 
  decimals 
  are 
  omitted: 
  Si02 
  51.7, 
  AI2O3 
  17.5, 
  "FeO" 
  

   (probably 
  at 
  least 
  half 
  FcaOs) 
  9.2, 
  MgO 
  8.8, 
  CaO 
  5.1, 
  and 
  "undeter- 
  

   mined" 
  (no 
  doubt 
  NaoO 
  + 
  HoO) 
  7.7%. 
  This 
  corresponds 
  more 
  or 
  

   less 
  to 
  a 
  mixture 
  of 
  labradorite 
  with 
  a 
  high 
  magnesium 
  glaucamphibole. 
  

   In 
  the 
  absence 
  of 
  optical 
  data, 
  however, 
  the 
  exact 
  identity 
  of 
  the 
  latter 
  

   could 
  not 
  be 
  established. 
  

  

  Another 
  occurrence 
  of 
  the 
  mineral 
  in 
  the 
  pre-Cambrian 
  was 
  studied 
  

   by 
  Mrs. 
  Eleonora 
  Bliss 
  Knopf 
  in 
  1913.^ 
  She 
  classed 
  the 
  mineral 
  

   as 
  glaucophane 
  on 
  the 
  basis 
  of 
  an 
  analysis 
  by 
  Dr. 
  Edwin 
  DeBarr, 
  but 
  

   judging 
  from 
  the 
  silica 
  percentage 
  of 
  83.3, 
  this 
  was 
  made 
  on 
  a 
  sample 
  

   containing 
  a 
  large 
  amount 
  of 
  quartz 
  in 
  addition 
  to 
  feldspar, 
  and 
  is 
  

   accordingly 
  unsuitable 
  for 
  establishing 
  the 
  exact 
  nature 
  of 
  the 
  min- 
  

   eral. 
  Mrs. 
  Knopf 
  obtained 
  in 
  addition 
  some 
  optical 
  measurements 
  

   agreeing 
  with 
  those 
  recorded 
  for 
  the 
  glaucamphibole 
  group, 
  but 
  not 
  

   characteristic 
  of 
  any 
  individual 
  member: 
  extinction 
  angle 
  X/c 
  = 
  3° 
  

   to 
  15°, 
  and 
  pleochroism 
  Z 
  blue 
  to 
  violet, 
  Y 
  pale 
  green, 
  and 
  X 
  colorless 
  

   to 
  pale 
  yellow. 
  

  

  While 
  the 
  senior 
  writer 
  was 
  connected 
  with 
  Lehigh 
  University, 
  

   Bethlehem, 
  Pa., 
  he 
  observed 
  glaucamphiboles 
  at 
  many 
  localities 
  in 
  the 
  

   region, 
  in 
  both 
  pre-Cambrian 
  and 
  Triassic 
  rocks. 
  On 
  removal 
  to 
  

   Washington, 
  he 
  presented 
  a 
  number 
  of 
  specimens 
  to 
  the 
  National 
  

   Museum, 
  and 
  made 
  a 
  study 
  of 
  their 
  optical 
  properties, 
  by 
  the 
  immer- 
  

   sion 
  method. 
  Much 
  of 
  the 
  material 
  proved 
  to 
  be 
  cryptocrystalline, 
  

   with 
  n 
  = 
  about 
  1.66 
  and 
  intense 
  blue 
  color. 
  At 
  some 
  localities, 
  

   however, 
  microscopically 
  fibrous 
  to 
  bladed 
  material 
  occurs, 
  and 
  this 
  

   gave 
  alpha 
  = 
  1.64 
  to 
  1.65, 
  beta 
  = 
  1.65, 
  gamma 
  = 
  1.66. 
  The 
  

   pleochroism 
  is 
  X 
  yellow, 
  Y 
  green, 
  Z 
  blue. 
  The 
  double 
  refraction 
  

   varies 
  from 
  one 
  specimen 
  to 
  another, 
  but 
  is 
  sometimes 
  so 
  low 
  that 
  

  

  1 
  Presented 
  at 
  the 
  meeting 
  of 
  the 
  Mineralogical 
  Society 
  of 
  America, 
  December 
  29, 
  192 
  L 
  

   PubHshed 
  by 
  permission 
  of 
  the 
  Secretary 
  of 
  the 
  vSmithsonian 
  Institution. 
  Received 
  

   Dec. 
  .31, 
  1921. 
  

  

  2 
  Second 
  Geol. 
  Survey 
  Penna. 
  Rept. 
  D 
  3, 
  II, 
  1: 
  93-94. 
  1883. 
  

  

  3 
  Bull. 
  Amer. 
  Muj;. 
  Nat. 
  Hist. 
  32: 
  517-526. 
  1913. 
  

  

  