﻿MAY 
  19, 
  1922 
  WHERRY 
  AND 
  SHANNON 
  : 
  CROCIDOLITE 
  243 
  

  

  anomalous 
  interference 
  colors 
  due 
  to 
  high 
  dispersion 
  in 
  some 
  inde- 
  

   terminate 
  direction 
  are 
  shown. 
  One 
  of 
  the 
  best 
  samples 
  for 
  optical 
  

   study 
  came 
  from 
  a 
  road 
  metal 
  quarry 
  southwest 
  of 
  the 
  town 
  of 
  Mohn- 
  

   ton, 
  Berks 
  County, 
  the 
  rock 
  being 
  a 
  highly 
  metamorphosed 
  Triassic 
  

   sandstone. 
  Other 
  noteworthy 
  localities 
  in 
  similar 
  rock, 
  as 
  well 
  as 
  in 
  

   the 
  Triassic 
  diabase 
  causing 
  the 
  alteration, 
  lie 
  three 
  miles 
  — 
  5 
  kilometers 
  

   — 
  south 
  of 
  the 
  city 
  of 
  Reading, 
  and 
  just 
  east 
  of 
  Little 
  Oley, 
  south 
  of 
  

   Boyertown, 
  Berks 
  County. 
  In 
  addition 
  to 
  the 
  pre-Cambrian 
  gneiss 
  

   occurrences 
  listed 
  by 
  Mrs. 
  Knopf, 
  it 
  is 
  abundant 
  in 
  these 
  rocks 
  north 
  

   of 
  Oley 
  Line, 
  Berks 
  County, 
  and 
  northeast 
  of 
  Dillingerville, 
  Lehigh 
  

   County. 
  It 
  also 
  occurs 
  for 
  some 
  miles 
  northeastward 
  from 
  Riegels- 
  

   ville, 
  Pa., 
  in 
  the 
  state 
  of 
  New 
  Jersey. 
  In 
  all 
  perhaps 
  fifty 
  localities 
  

   are 
  known. 
  ^ 
  

  

  TABLE 
  1. 
  — 
  Analysis 
  and 
  Ratios 
  of 
  Crocidolite 
  from 
  Oley 
  Line, 
  Pa. 
  

  

  Becoming 
  interested 
  in 
  the 
  identity 
  of 
  the 
  mineral, 
  the 
  junior 
  author 
  

   analyzed 
  a 
  sample 
  from 
  the 
  locality 
  north 
  of 
  Oley 
  Line, 
  which 
  was 
  

   kindly 
  selected 
  and 
  purified 
  by 
  Mr. 
  C. 
  S. 
  Ross 
  of 
  the 
  U. 
  S. 
  Geological 
  

   Survey, 
  and 
  proved 
  to 
  be 
  cryptocrystalline 
  and 
  homogeneous 
  on 
  micro- 
  

   scopic 
  examination. 
  The 
  analysis, 
  the 
  first 
  made 
  on 
  pure 
  material, 
  

   showed 
  the 
  mineral 
  to 
  be 
  a 
  semimagnesium 
  crocidolite, 
  with 
  the 
  

   formula 
  H2O 
  . 
  NaoO 
  . 
  MgO 
  . 
  FeO 
  . 
  FcsOg 
  . 
  GSiOs. 
  

  

  The 
  high 
  percentage 
  of 
  titanium 
  present 
  suggests 
  that 
  this 
  element, 
  

   in 
  its 
  lower 
  state 
  of 
  oxidation, 
  may 
  partially 
  account 
  for 
  the 
  extremely 
  

   intense 
  color 
  of 
  the 
  mineral, 
  although 
  admittedly 
  part 
  of 
  the 
  color 
  is 
  

   due 
  to 
  iron. 
  Titanium 
  has 
  therefore 
  been 
  regarded 
  as 
  replacing 
  

   aluminium 
  and 
  iron, 
  rather 
  than 
  silicon. 
  The 
  low 
  content 
  of 
  alkalies 
  

  

  * 
  Professor 
  A. 
  H. 
  Phillips 
  reports 
  it 
  also 
  in 
  the 
  highlands 
  of 
  New 
  York 
  State. 
  It 
  is 
  rep- 
  

   resented 
  in 
  some 
  mineral 
  collections 
  under 
  the 
  name 
  vivianite. 
  

  

  