﻿638 
  i?. 
  0. 
  Wells 
  — 
  New 
  Occurrence 
  of 
  Cuprodescloizite. 
  

  

  requirements 
  of 
  the 
  formula 
  2Pb0.2CuO.Y 
  2 
  5 
  .H 
  2 
  and 
  a 
  

   deficiency 
  of 
  copper, 
  as 
  shown 
  by 
  the 
  following 
  comparison 
  : 
  

  

  PbO 
  

  

  CuO 
  

  

  ZnO 
  ._ 
  

  

  vo 
  

  

  Theory 
  for 
  

   PbV0 
  4 
  .CuOH 
  

  

  -_ 
  55*4 
  

  

  19-8 
  

  

  22-6 
  

  

  Found 
  

  

  55-6 
  

  

  17-0 
  

  

  •3 
  

  

  21-2 
  

  

  AsO 
  

  

  

  1-3 
  

  

  2^5 
  

  

  PO 
  

  

  

  "2 
  

  

  2 
  6 
  

  

  H 
  

  

  2'2 
  

  

  3-6 
  

  

  a 
  

  

  

  

  100-0 
  99-2 
  

  

  The 
  lead 
  content, 
  however, 
  agrees 
  very 
  well 
  with 
  that 
  

   required 
  for 
  cuprodescloizite. 
  It 
  is 
  evident 
  that 
  the 
  elements 
  

   of 
  the 
  minerals 
  of 
  the 
  olivinite 
  group 
  often 
  suffer 
  extensive 
  

   replacement. 
  Here 
  we 
  have 
  copper 
  appearing 
  almost 
  wholly 
  

   in 
  place 
  of 
  the 
  zinc 
  of 
  descloizite, 
  the 
  intermediate 
  members 
  

   being 
  already 
  known. 
  The 
  present 
  mineral, 
  then, 
  represents 
  

   the 
  copper 
  end 
  of 
  the 
  cuprodescloizite 
  series. 
  It 
  may 
  be 
  that 
  

   the 
  entrance 
  of 
  the 
  copper 
  favors 
  the 
  addition 
  of 
  another 
  

   molecule 
  of 
  water. 
  Several 
  investigators 
  have 
  commented 
  on 
  

   the 
  tendency 
  of 
  the 
  minerals 
  of 
  this 
  series 
  to 
  carry 
  a 
  slight 
  

   excess 
  of 
  water 
  which 
  is 
  certainly 
  not 
  hygroscopic* 
  Chro- 
  

   mium 
  lias 
  not 
  been 
  reported 
  in 
  any 
  descloizite 
  heretofore. 
  It 
  

   suggests 
  a 
  slight 
  admixture 
  of 
  a 
  compound 
  analogous 
  to 
  

   vauquelinite. 
  

  

  Genesis. 
  — 
  The 
  constituents 
  of 
  this 
  mineral, 
  lead, 
  copper, 
  

   vanadium, 
  arsenic, 
  etc., 
  in 
  combination 
  yield 
  " 
  insoluble 
  " 
  com- 
  

   pounds 
  and 
  were, 
  therefore, 
  probably 
  assembled 
  in 
  very 
  dilute 
  

   solutions. 
  

  

  The 
  stalactitic 
  form 
  of 
  the 
  mineral 
  indicates 
  that 
  it 
  crystal- 
  

   lized 
  by 
  the 
  evaporation 
  of 
  downward 
  migrating 
  solutions 
  and 
  

   its 
  chemical 
  character 
  shows 
  that 
  the 
  solutions 
  were 
  products 
  

   of 
  oxidation. 
  With 
  the 
  data 
  at 
  hand 
  it 
  is 
  impossible 
  to 
  ascribe 
  

   any 
  special 
  geologic 
  significance 
  to 
  its 
  origin. 
  Its 
  chemical 
  

   composition, 
  however, 
  is 
  significant. 
  Since 
  the 
  chromate 
  of 
  

   lead 
  is 
  very 
  insoluble 
  like 
  the 
  vanadate, 
  it 
  is 
  evident 
  that 
  vana- 
  

   dium 
  was 
  present 
  in 
  the 
  solution 
  in 
  excess 
  of 
  chromium. 
  

   Some 
  tentative 
  experiments 
  have 
  shown 
  that 
  when 
  lead 
  and 
  

   copper 
  compete 
  for 
  a 
  soluble 
  vanadate, 
  lead 
  vanadate 
  is 
  the 
  prin- 
  

   cipal 
  product. 
  Hence 
  it 
  seems 
  reasonable 
  to 
  assume 
  that 
  lead 
  

   was 
  scarcer 
  than 
  copper 
  in 
  the 
  solution 
  from 
  which 
  the 
  mineral 
  

   formed. 
  With 
  present 
  data 
  it 
  is 
  impossible 
  to 
  make 
  any 
  defi- 
  

   nite 
  statement, 
  however, 
  about 
  the 
  proportion 
  of 
  vanadium 
  

   with 
  respect 
  to 
  the 
  copper 
  in 
  the 
  mother 
  solution. 
  

  

  * 
  Cf. 
  Penfield, 
  this 
  Journal, 
  xxvi, 
  364, 
  1883. 
  

  

  