﻿168 
  E. 
  V. 
  Shannon 
  — 
  Bismutoplagionite. 
  

  

  The 
  new 
  mineral 
  thus 
  agrees 
  almost 
  exactly 
  with 
  the 
  

   formula 
  5Pb$.4Bi 
  2 
  S 
  3 
  , 
  a 
  small 
  proportion 
  of 
  the 
  bismuth 
  

   being 
  replaced 
  by 
  antimony. 
  Although 
  but 
  a 
  single 
  analy- 
  

   sis 
  was 
  made 
  it 
  is 
  considered 
  improbable 
  that 
  the 
  mineral 
  

   can 
  be 
  regarded 
  as 
  a 
  variety 
  of 
  galenobismutite. 
  The 
  

   sample 
  analyzed 
  was 
  selected 
  with 
  extreme 
  care 
  by 
  hand 
  

   picking, 
  each 
  fragment 
  being 
  examined 
  under 
  the 
  micro- 
  

   scope 
  and 
  chunks 
  of 
  the 
  sulphide 
  aggregate 
  which 
  showed 
  

   any 
  minerals 
  other 
  than 
  pyrite 
  and 
  the 
  fibrous 
  bismuth 
  

   mineral 
  were 
  not 
  crushed 
  in 
  the 
  lot 
  from 
  which 
  material 
  

   for 
  analysis 
  was 
  picked. 
  It 
  was 
  necessary 
  to 
  determine 
  

   sulphur 
  by 
  difference 
  but 
  the 
  value 
  thus 
  obtained 
  is 
  al- 
  

   most 
  exactly 
  that 
  required 
  to 
  convert 
  the 
  metals 
  to 
  their 
  

   respective 
  sulphides. 
  The 
  iron 
  found 
  in 
  solution 
  is 
  de- 
  

   ducted 
  as 
  pyrite. 
  It 
  is 
  surprising 
  that 
  the 
  pyrite 
  was 
  

   not 
  more 
  completely 
  attacked 
  by 
  the 
  long 
  treatment 
  with 
  

   hot 
  hydrochloric 
  acid 
  to 
  which 
  it 
  was 
  subjected. 
  

  

  Plagionite, 
  despite 
  its 
  unusual 
  ratios, 
  is 
  a 
  mineral 
  of 
  

   definite 
  composition 
  and 
  form 
  and 
  that 
  it 
  should 
  have 
  a 
  

   bismuth 
  analogue 
  is 
  to 
  be 
  expected. 
  The 
  two 
  minerals 
  

   are 
  isomorphous 
  as 
  indicated 
  by 
  the 
  small 
  antimony 
  

   content 
  in 
  the 
  present 
  mineral. 
  Liveingite 
  2 
  also 
  seems 
  to 
  

   be 
  a 
  well-defined 
  member 
  of 
  the 
  same 
  group. 
  The 
  for- 
  

   mulae 
  of 
  the 
  three 
  members 
  of 
  this 
  immediate 
  group 
  are 
  

   then: 
  

  

  Plagionite 
  5PbS 
  4Sb 
  2 
  ^ 
  

  

  Bismutoplagionite 
  5PbS 
  4Bi 
  2 
  S 
  3 
  

  

  Liveingite 
  5PbS 
  4As 
  2 
  S 
  3 
  

  

  The 
  composition 
  given 
  in 
  the 
  analysis 
  with 
  the 
  anti- 
  

   mony 
  recalculated 
  to 
  bismuth 
  is 
  compared 
  with 
  the 
  theo- 
  

   retical 
  composition 
  of 
  the 
  bismuth 
  compound 
  and 
  with 
  

   galenobismutite 
  in 
  the 
  following 
  table 
  : 
  

  

  I 
  II 
  III 
  

  

  per 
  cent 
  per 
  cent 
  per 
  cent 
  

  

  PbS 
  37-34 
  36-87 
  31-83 
  

  

  Bi 
  2 
  S 
  3 
  62-66 
  63-13 
  68-17 
  

  

  I. 
  Analysis 
  of 
  bismutoplagionite, 
  Sb 
  calculated 
  to 
  Bi 
  and 
  the 
  

   whole 
  reduced 
  to 
  100% 
  

  

  II. 
  Composition 
  to 
  satisfy 
  formula 
  5PbS 
  4Bi 
  2 
  S 
  3 
  . 
  

   III. 
  Galenobismutite, 
  composition 
  to 
  satisfy 
  formula 
  PbS,Bi 
  2 
  S 
  3 
  . 
  

  

  2 
  Min. 
  Mag. 
  13, 
  160. 
  

  

  