﻿Penfield 
  and 
  Warren 
  — 
  Minerals 
  from 
  FranMin^ 
  N. 
  J. 
  315 
  

  

  tlie 
  character 
  of 
  the 
  double 
  refraction 
  of 
  glaucochroite 
  are 
  

   like 
  those 
  of 
  monticellite 
  as 
  determined 
  by 
  Penfield 
  and 
  Forbes."^ 
  

   The 
  indices 
  of 
  refraction 
  for 
  yellow 
  light 
  and 
  the 
  divergence 
  

   of 
  the 
  optical 
  axes, 
  2Y, 
  of 
  glaucochroite, 
  monticellite 
  and 
  

   chrysolite 
  are 
  given 
  below 
  for 
  comparison 
  : 
  

  

  a 
  

   Glaucochroite, 
  1-686 
  

   Monticellite, 
  1-6505 
  

   Chrysolite,! 
  1-661 
  

  

  Yery 
  pure 
  material 
  for 
  the 
  chemical 
  analysis 
  was 
  obtained 
  by 
  

   picking 
  out 
  the 
  small 
  prisma^tic 
  crystals 
  which 
  separated 
  readily 
  

   from 
  the 
  matrix. 
  The 
  results 
  of 
  the 
  analysis 
  by 
  Warren 
  are 
  

   as 
  follows 
  : 
  

  

  /5 
  

  

  y 
  

  

  y-a 
  

  

  2 
  Y 
  over 
  a 
  

  

  1-722 
  

  

  1-735 
  

  

  0-049 
  

  

  60° 
  51' 
  

  

  1-6616 
  

  

  1-6679 
  

  

  0-0174 
  

  

  75° 
  2' 
  

  

  1-678 
  

  

  1-697 
  

  

  0-036 
  

  

  92° 
  14' 
  

  

  SiO. 
  

   MnO 
  

   CaO 
  

   PbO 
  

   FeO 
  

  

  31-48 
  

   38-00 
  

   28-95 
  

   1-74 
  

   trace 
  

  

  Ratio. 
  

   •524 
  

   •535 
  

   •517 
  

  

  1-00 
  

  

  1-02 
  

  

  •99 
  

  

  Corrected 
  

   analysis. 
  

  

  31-98 
  

   38-60 
  

   29-42 
  

  

  Theory 
  for 
  

   CaMnSiO^ 
  

  

  32-08 
  

   37^97 
  

   29-95 
  

  

  100-00 
  

  

  100-00 
  

  

  100-17 
  

  

  Leaving 
  out 
  of 
  consideration 
  the 
  small 
  amount 
  of 
  PbO, 
  which, 
  

   owing 
  to 
  its 
  high 
  molecular 
  weiglit, 
  had 
  only 
  a 
  slight 
  effect 
  

   upon 
  the 
  ratio, 
  the 
  ratio 
  of 
  SiO^ 
  : 
  MnO: 
  CaO=l-00 
  : 
  1-02: 
  

   0-99, 
  or 
  a 
  very 
  close 
  approximation 
  to 
  1:1:1. 
  The 
  formula 
  

   of 
  glaucochroite 
  is 
  therefore 
  CaMnSiO^. 
  that 
  of 
  monticellite 
  

   being 
  CaMgSiO^. 
  With 
  the 
  above 
  analysis 
  we 
  have 
  given 
  the 
  

   corrected 
  analysis, 
  after 
  disregarding 
  1-74 
  per 
  cent 
  of 
  PbO 
  and 
  

   calculating 
  to 
  100 
  per 
  cent, 
  and 
  also 
  the 
  theoretical 
  composi- 
  

   tion 
  corresponding 
  to 
  the 
  formula 
  CaMnSiO^. 
  Glaucochroite 
  

   takes 
  therefore 
  a 
  place 
  in 
  the 
  system 
  of 
  mineralogy 
  next 
  to 
  

   monticellite 
  as 
  a 
  member 
  of 
  the 
  chrysolite 
  group. 
  

  

  Glaucochroite 
  fuses 
  quietly 
  before 
  the 
  blowpipe 
  at 
  about 
  3-5 
  

   to 
  a 
  brownish 
  black 
  globule, 
  and 
  imparts 
  no 
  color 
  to 
  the 
  flame. 
  

   The 
  powdered 
  mineral 
  dissolves 
  easily 
  in 
  hydrochloric 
  acid, 
  and 
  

   the 
  solution 
  yields 
  gelatinous 
  silica 
  upon 
  evaporation. 
  A 
  little 
  

   of 
  the 
  concentrated 
  solution, 
  when 
  brought 
  in 
  contact 
  with 
  a 
  

   drop 
  of 
  sulphuric 
  acid 
  on 
  a 
  watch 
  glass, 
  giv^es 
  a 
  precipitate 
  of 
  

   calcium 
  sulphate. 
  With 
  either 
  the 
  borax 
  or 
  sodium 
  carbonate 
  

   beads 
  a 
  strong 
  reaction 
  for 
  manganese 
  is 
  obtained. 
  

  

  So 
  far 
  as 
  known, 
  only 
  a 
  small 
  amount 
  of 
  glaucochroite 
  has 
  

   been 
  found. 
  Its 
  crystals 
  occur 
  imbedded 
  in 
  a 
  white 
  matrix, 
  

   nasonite 
  (see 
  beyond), 
  and 
  intimately 
  associated 
  with 
  brown 
  

  

  * 
  This 
  Journal, 
  1, 
  p. 
  135, 
  1896. 
  

  

  f 
  Des 
  Cloizeaux, 
  Memoirs 
  tie 
  ITnstitute 
  de 
  France, 
  T. 
  xviii, 
  p. 
  591. 
  

  

  