﻿344: 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  Pseudomorph 
  after 
  pyrite, 
  Louisa 
  County, 
  Virginia 
  

   (from 
  Prof. 
  Holden). 
  — 
  Felted 
  fibers 
  of 
  goethite 
  having 
  y 
  

   near 
  2-27, 
  and 
  a 
  near 
  2-20. 
  Small 
  amounts 
  of 
  felted 
  

   grains 
  of 
  turgite 
  are 
  scattered 
  irregularly 
  through 
  the 
  

   brown 
  ore. 
  

  

  Fibrous 
  goethite 
  on 
  and 
  under 
  lepidocrocite, 
  Rossbach, 
  

   Germany. 
  — 
  Small 
  hemispherical 
  radial-fibrous 
  aggre- 
  

   gates 
  on 
  lepidocrocite 
  scales, 
  y 
  = 
  2-26 
  - 
  2-28, 
  a 
  = 
  2-18 
  — 
  

   2-20. 
  The 
  scales 
  grew 
  upon 
  fibrous 
  goethite 
  having 
  y 
  and 
  

   p 
  = 
  2-32 
  - 
  2-29, 
  a 
  = 
  2-18 
  - 
  2-19. 
  

  

  Fibrous 
  goethite 
  under 
  lepidocrocite, 
  Miisen, 
  Ger- 
  

   many. 
  — 
  Two 
  structures 
  are 
  apparent: 
  (1) 
  the 
  fibrous 
  

   form 
  cigar-shaped 
  bundles; 
  (2) 
  these 
  bundles 
  are 
  

   arranged 
  in 
  sub-parallel 
  to 
  radiating 
  groups 
  which 
  do 
  not 
  

   extinguish 
  well 
  ; 
  y 
  about 
  2-28, 
  a 
  = 
  2-16 
  - 
  2-18. 
  

  

  Fibrous 
  goethite, 
  R. 
  C. 
  1489. 
  Iron 
  Mountain 
  Mine, 
  

   California. 
  (From 
  Prof. 
  Graton.) 
  — 
  Fibrous, 
  yellowish 
  

   layers 
  in 
  the 
  walls 
  of 
  a 
  vug 
  containing 
  residual 
  sulphides. 
  

   This 
  is 
  remarkable 
  because 
  microscopic 
  splinters 
  have 
  

   (1) 
  what 
  appears 
  to 
  be 
  very 
  different 
  absorption 
  for 
  light 
  

   in 
  the 
  two 
  principal 
  directions 
  and 
  the 
  character 
  of 
  the 
  

   absorption 
  is 
  the 
  reverse 
  of 
  that 
  in 
  all 
  other 
  specimens 
  

   observed, 
  that 
  is, 
  is 
  greatest 
  across 
  the 
  fibers; 
  (2) 
  great 
  

   porosity; 
  (3) 
  when 
  pores 
  are 
  filled 
  with 
  liquid 
  having 
  n 
  

   about 
  2-0, 
  apparent 
  homogeneity 
  when 
  seen 
  in 
  light 
  

   vibrating 
  parallel 
  to 
  the 
  length 
  of 
  the 
  fibers 
  and 
  non- 
  

   homogeneity 
  across 
  the 
  fibers. 
  In 
  the 
  latter 
  position 
  the 
  

   structure 
  appears 
  fibrous, 
  with 
  the 
  diameter 
  of 
  the 
  fibers 
  

   about 
  lfi. 
  All 
  three 
  characteristics 
  would 
  appear 
  in 
  struc- 
  

   tures 
  somewhat 
  coarser 
  than 
  those 
  described 
  under 
  goe- 
  

   thite 
  above. 
  The 
  anomalous 
  absorption 
  would 
  then 
  be 
  

   explained 
  by 
  the 
  lateral 
  diffusion 
  of 
  light 
  at 
  the 
  compara- 
  

   tively 
  large 
  surfaces 
  between 
  differently 
  oriented 
  goethite 
  

   fibers. 
  The 
  apparent 
  refractive 
  indices 
  of 
  this 
  material 
  

   are 
  decidedly 
  lower 
  than 
  for 
  any 
  other 
  fibrous 
  goethite 
  

   examined; 
  y 
  = 
  2-ll, 
  a 
  (which 
  could 
  not 
  be 
  determined 
  

   accurately) 
  is 
  about 
  2-05. 
  

  

  LIMONITE. 
  57 
  

  

  1206 
  Cananea, 
  New 
  Mexico. 
  58 
  — 
  Transported 
  ore 
  in 
  vug, 
  

   outside 
  hard. 
  The 
  earthy 
  ore 
  within 
  and 
  the 
  hard 
  crust 
  

  

  07 
  See 
  general 
  description, 
  p. 
  321. 
  The 
  first 
  five 
  of 
  these 
  specimens 
  were 
  

   collected 
  by 
  Prof. 
  L. 
  C. 
  Graton, 
  1914, 
  and 
  the 
  occurrences 
  are 
  given 
  as 
  

   described 
  by 
  him. 
  

  

  "Analyzed, 
  Table 
  III. 
  

  

  