﻿Penfield 
  and 
  Warren 
  — 
  Minerals 
  from 
  FranMin^ 
  N. 
  J. 
  341 
  

  

  grading 
  to 
  pale, 
  somewhat 
  greenish-yellow 
  at 
  the 
  terminated 
  

   end. 
  On 
  some 
  very 
  small 
  individuals 
  the 
  delicate 
  rose 
  color 
  

   was 
  observed 
  throughout 
  the 
  whole 
  length 
  of 
  the 
  crystals. 
  

   With 
  crossed 
  nicols 
  the 
  crystals 
  show 
  an 
  extinction 
  when 
  their 
  

   longer 
  or 
  symmetry 
  axis 
  is 
  parallel 
  to 
  the 
  plane 
  of 
  the 
  polar- 
  

   izer. 
  In 
  convergent 
  light 
  something 
  of 
  the 
  outer 
  rings 
  of 
  the 
  

   biaxial 
  interference 
  figure 
  could 
  be 
  seen, 
  accompanied 
  by 
  a 
  

   dark 
  bar, 
  indicating 
  plainly 
  that 
  the 
  optical 
  axes 
  are 
  in 
  the 
  

   symmetry 
  plane. 
  By 
  rotating 
  a 
  crystal, 
  when 
  immersed 
  in 
  

   the 
  potassium 
  mercuric-iodide 
  solution, 
  the 
  optical 
  axes 
  could 
  be 
  

   brought 
  separately 
  to 
  the 
  center 
  of 
  the 
  field 
  and 
  their 
  diver- 
  

   gence 
  2 
  Y 
  was 
  found 
  to 
  be 
  approximately 
  50°. 
  

  

  The 
  luster 
  of 
  the 
  hancockite 
  crystals 
  is 
  vitreous, 
  and 
  the 
  

   hardness 
  is 
  about 
  6*5-7. 
  Owing 
  to 
  the 
  small 
  size 
  of 
  the 
  crys- 
  

   tals 
  and 
  their 
  intimate 
  association 
  with 
  garnet, 
  axinite 
  and 
  

   willemite, 
  considerable 
  difficulty 
  was 
  experienced 
  in 
  finding 
  a 
  

   specimen 
  from 
  which 
  a 
  sufficient 
  quantity 
  of 
  pure 
  material 
  

   could 
  be 
  obtained 
  for 
  analysis. 
  A 
  specimen, 
  however, 
  finally 
  

   came 
  to 
  us 
  through 
  Mr. 
  Hancock, 
  consisting 
  of 
  a 
  cellular 
  mass 
  

   in 
  which 
  the 
  walls 
  and 
  the 
  drusy 
  lining 
  consisted 
  chiefly 
  of 
  

   hancockite. 
  By 
  crushing 
  this 
  specimen, 
  picking 
  out 
  the 
  small 
  

   fragments 
  and 
  examining 
  them 
  with 
  a 
  lens, 
  it 
  was 
  possible 
  to 
  

   obtain 
  the 
  mineral 
  almost 
  absolutely 
  free 
  from 
  the 
  associated 
  

   garnet 
  and 
  axinite, 
  which 
  could 
  be 
  distinguished 
  by 
  their 
  

   lighter 
  color. 
  An 
  attempt 
  to 
  separate 
  the 
  minerals 
  by 
  dif- 
  

   ferences 
  in 
  their 
  specific 
  gravity 
  was 
  not 
  successful. 
  The 
  

   specific 
  gravity 
  of 
  the 
  carefully 
  selected 
  material 
  was 
  found 
  to 
  

   be 
  4-030. 
  

  

  Concerning 
  the 
  method 
  of 
  analysis 
  the 
  only 
  points 
  which 
  

   need 
  to 
  be 
  specially 
  commented 
  upon 
  are 
  the 
  following 
  : 
  After 
  

   separation 
  of 
  the 
  silica, 
  the 
  lead 
  was 
  precipitated 
  with 
  hydrogen 
  

   sulphide 
  and 
  subsequently 
  converted 
  into 
  sulphate 
  and 
  weighed. 
  

   The 
  iron 
  and 
  alumina 
  were 
  separated 
  from 
  the 
  bivalent 
  metals 
  

   by 
  a 
  basic 
  acetate 
  precipitation, 
  reprecipitated 
  by 
  ammonia 
  and 
  

   weighed 
  as 
  oxides, 
  the 
  iron 
  being 
  estimated 
  subsequently 
  by 
  

   means 
  of 
  potassium 
  permanganate. 
  The 
  calcium 
  and 
  strontium 
  

   were 
  converted 
  into 
  nitrates 
  and 
  separated 
  by 
  means 
  of 
  amyl 
  

   alcohol 
  as 
  directed 
  by 
  Browning."^ 
  Water 
  was 
  estimated 
  by 
  

   loss 
  on 
  ignition. 
  Careful 
  tests 
  failed 
  to 
  reveal 
  the 
  presence 
  of 
  

   any 
  ferrous 
  iron. 
  The 
  deep 
  color 
  of 
  the 
  crystals 
  at 
  first 
  sug- 
  

   gested 
  the 
  idea 
  that 
  the 
  mineral 
  would 
  be 
  rich 
  in 
  manganese, 
  

   which 
  is 
  by 
  no 
  means 
  the 
  case. 
  The 
  color, 
  however, 
  is 
  prob- 
  

   ably 
  due 
  to 
  the 
  presence 
  of 
  some 
  higher 
  oxide 
  of 
  manganese 
  

   which 
  is 
  known 
  to 
  impart 
  an 
  intense 
  color 
  to 
  silicates 
  and 
  was 
  

   estimated 
  by 
  the 
  method 
  described 
  by 
  Penfield.f 
  

  

  *This 
  Journal, 
  xliii, 
  p. 
  50, 
  1892. 
  f 
  Ibid 
  , 
  xlvi, 
  p. 
  291, 
  1893. 
  

  

  