﻿W. 
  F. 
  Hillebrand 
  — 
  Analyses 
  of 
  Uraninite. 
  393 
  

  

  obtained. 
  It 
  is 
  not 
  known 
  wherein 
  the 
  loss 
  is 
  to 
  be 
  sought. 
  

   Like 
  the 
  great 
  mass 
  of 
  the 
  Bohemian 
  mineral 
  this 
  showed 
  no 
  

   evidence 
  of 
  ever 
  having 
  been 
  crystallized, 
  and 
  as 
  in 
  that 
  also 
  

   rare 
  earths 
  are 
  absent, 
  and 
  also 
  nitrogen 
  except 
  for 
  an 
  uncertain 
  

   trace. 
  

  

  From 
  the 
  analyses 
  of 
  uraninite 
  thus 
  far 
  made 
  it 
  appears 
  

   that 
  the 
  species 
  may 
  be 
  broadly 
  divided 
  into 
  two 
  groups, 
  the 
  

   one 
  of 
  which 
  is 
  characterized 
  by 
  the 
  presence 
  of 
  rare 
  earths, 
  

   the 
  other 
  by 
  their 
  absence. 
  With 
  the 
  former 
  group 
  nitrogen 
  

   appears 
  to 
  be 
  invariably 
  associated, 
  while 
  in 
  the 
  latter 
  it 
  is 
  

   present, 
  if 
  at 
  all, 
  only 
  in 
  minute 
  quantity. 
  Besides 
  these 
  

   chemical 
  differences 
  there 
  is 
  one 
  of 
  another 
  kind, 
  for 
  probably 
  

   all 
  varieties 
  of 
  the 
  first 
  group 
  occur 
  in 
  more 
  or 
  less 
  well 
  defined 
  

   crystals, 
  while 
  the 
  members 
  of 
  the 
  second 
  group 
  are 
  generally, 
  

   if 
  not 
  altogether, 
  massive 
  and 
  free 
  from 
  crystalline 
  form. 
  These 
  

   differences 
  suggest 
  naturally 
  a 
  dissimilarity 
  of 
  origin 
  and 
  envi- 
  

   ronment. 
  Examination 
  shows 
  that 
  the 
  manner 
  of 
  occurrence 
  

   and 
  the 
  association 
  of 
  other 
  minerals 
  is 
  different 
  and 
  in 
  such 
  a 
  

   way 
  as 
  to 
  render 
  an 
  unlike 
  immediate 
  origin 
  probable. 
  All 
  of 
  

   the 
  rare 
  earth 
  uraninites, 
  with 
  exception 
  of 
  the 
  zirconiferous 
  

   variety 
  from 
  Black 
  Hawk, 
  Colorado, 
  occur 
  as 
  an 
  apparently 
  

   original 
  constituent 
  of 
  coarse 
  granites 
  (chiefly 
  pegmatitic), 
  

   while 
  the 
  others 
  are 
  evidently 
  of 
  secondary 
  formation, 
  as 
  evi- 
  

   denced 
  by 
  their 
  presence 
  in 
  metalliferous 
  veins 
  in 
  more 
  or 
  less 
  

   intimate 
  association 
  with 
  numerous 
  sulphides 
  of 
  silver, 
  lead, 
  

   cobalt, 
  nickel, 
  iron, 
  zinc, 
  copper, 
  etc. 
  The 
  Colorado 
  variety 
  

   occupies 
  an 
  anomalous 
  position 
  as 
  regards 
  the 
  two 
  groups. 
  I 
  

   prefer 
  to 
  regard 
  it 
  provisionally 
  as 
  a 
  member 
  of 
  the 
  second 
  

   group, 
  where 
  its 
  mode 
  of 
  occurrence 
  and 
  want 
  of 
  crystalline 
  

   form 
  as 
  well 
  as 
  small 
  percentage 
  of 
  nitrogen 
  seem 
  to 
  place 
  it, 
  

   although 
  its 
  zirconia 
  and 
  traces 
  of 
  other 
  earths 
  would 
  admit 
  

   it 
  to 
  the 
  first. 
  

  

  Attention 
  is 
  called 
  to 
  the 
  above 
  points 
  merely 
  to 
  show 
  that 
  

   the 
  chemical 
  and 
  physical 
  differences 
  of 
  the 
  two 
  groups 
  may 
  

   be 
  susceptible 
  of 
  more 
  simple 
  explanation 
  than 
  would 
  appear 
  

   from 
  the 
  face 
  of 
  the 
  analyses. 
  

  

  Laboratory 
  U. 
  S. 
  Geological 
  Survey, 
  Washinton, 
  D. 
  C, 
  June. 
  

  

  