﻿196 
  JOURNAIv 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO, 
  8 
  

  

  contains 
  scattered 
  cavities 
  varying 
  up 
  to 
  several 
  inches 
  in 
  diameter, 
  

   the 
  first 
  lining 
  of 
  which 
  consists 
  of 
  small 
  blade-like 
  crystals 
  of 
  a 
  plagio- 
  

   clase 
  identified 
  by 
  its 
  optical 
  properties 
  as 
  oligoclase-andesine. 
  Upon 
  

   this 
  crust 
  rest 
  the 
  disseminated 
  white 
  crystals 
  of 
  cristobalite 
  and 
  mi- 
  

   nute 
  octahedrons 
  of 
  magnetite 
  following 
  which 
  was 
  deposited 
  siderite 
  

   ("sphaerosiderite") 
  in 
  small 
  spherical 
  masses. 
  Later 
  successive 
  

   deposits 
  include, 
  in 
  the 
  order 
  named, 
  pyrite, 
  iron 
  opal, 
  second 
  genera- 
  

   tion 
  sphaerosiderite, 
  calcite, 
  white 
  opal, 
  and 
  hyalite. 
  Weathering 
  has 
  

   converted 
  some 
  of 
  the 
  nodules 
  of 
  siderite 
  to 
  secondary 
  pseudomorphs 
  

   of 
  limonite 
  and 
  goethite. 
  

  

  The 
  cristobalite 
  forms 
  sub-translucent 
  white 
  crystals 
  0.5 
  mm. 
  or 
  less 
  

   in 
  diameter 
  irregularly 
  scattered 
  over 
  the 
  interior 
  of 
  the 
  cavities. 
  

   These 
  have 
  a 
  feeble 
  luster 
  and 
  a 
  white 
  porcelain-like 
  appearance. 
  

   It 
  was 
  possible 
  to 
  detach 
  several 
  of 
  the 
  cristobalites 
  from 
  the 
  matrix 
  

   and 
  to 
  measure 
  them 
  on 
  the 
  2-circle 
  goniometer 
  with 
  sufficient 
  accuracy 
  

   to 
  identify 
  the 
  forms 
  and 
  to 
  indicate 
  isometric 
  symmetry. 
  Most 
  of 
  

   the 
  crystals 
  are 
  cuboctahedrons 
  with 
  the 
  faces 
  of 
  the 
  cube 
  and 
  octahe- 
  

   dron 
  equally 
  developed. 
  The 
  faces 
  are 
  commonly 
  concave 
  or 
  divided 
  

   by 
  sutures 
  so 
  as 
  to 
  give 
  several 
  signals 
  while 
  the 
  cube 
  faces 
  often 
  

   show 
  a 
  confusion 
  of 
  slightly 
  re-entrant 
  angles 
  suggesting 
  complex 
  

   twinning 
  and 
  grading 
  toward 
  the 
  spherulitic 
  forms 
  characteristic 
  of 
  the 
  

   mineral. 
  Rarely 
  a 
  crystal 
  is 
  observed 
  which 
  shows 
  no 
  indication 
  of 
  

   this 
  twinning 
  and 
  which 
  has 
  the 
  exterior 
  form 
  of 
  a 
  simple 
  isometric 
  

   crystal. 
  The 
  best 
  of 
  these 
  measured 
  was 
  a 
  cuboctahedron 
  with 
  its 
  

   edges 
  beveled 
  by 
  narrow 
  faces 
  of 
  the 
  trapezohedron. 
  The 
  latter 
  form 
  

   has 
  not 
  previously 
  been 
  observed 
  on 
  crystals 
  of 
  this 
  mineral. 
  

  

  Under 
  the 
  microscope 
  the 
  material 
  has 
  a 
  feeble 
  birefringence 
  and 
  

   has 
  a 
  refractive 
  index 
  of 
  1.485=*= 
  .003. 
  The 
  crystals 
  are 
  unchanged 
  

   by 
  boiling 
  in 
  hydrochloric 
  acid 
  and 
  are 
  volatilized 
  without 
  leaving 
  

   any 
  residue 
  by 
  evaporation 
  with 
  hydrofluoric 
  and 
  sulphuric 
  acids. 
  

   Although 
  cristobalite 
  has 
  recently 
  been 
  described 
  from 
  several 
  locali- 
  

   ties 
  in 
  the 
  United 
  States 
  this 
  is 
  the 
  first 
  locality 
  in 
  this 
  country 
  to 
  

   furnish 
  measurable 
  crystals 
  of 
  this 
  mineral. 
  

  

  CRYSTALLOGRAPHY. 
  — 
  Review 
  of 
  the 
  optical-crystallographic 
  prop- 
  

   erties 
  of 
  calcium 
  oxalate 
  monohydrate} 
  Edgar 
  T. 
  Wherry, 
  

   Bureau 
  of 
  Chemistry. 
  

   The 
  mineral 
  whewellite, 
  calcium 
  oxalate 
  monohydrate, 
  was 
  dis- 
  

   covered 
  in 
  1840, 
  and 
  has 
  subsequently 
  been 
  the 
  subject 
  of 
  considerable 
  

   * 
  Received 
  Dec. 
  3, 
  1921. 
  

  

  