﻿OCT. 
  19, 
  1922 
  WASHINGTON 
  : 
  JADE 
  PEBBUE 
  FROM 
  COP 
  AN 
  389 
  

  

  which 
  was 
  analysed) 
  is 
  of 
  a 
  nearly 
  uniform, 
  pale 
  gray 
  green, 
  between 
  

   Ridgway's 
  pea- 
  and 
  sage-green. 
  The 
  larger 
  is 
  decidedly 
  whitish 
  on 
  

   the 
  natural 
  surface, 
  which 
  shows 
  slight 
  pitting; 
  and 
  this 
  has 
  evidently 
  

   been 
  somewhat 
  weathered, 
  as 
  is 
  also 
  shown 
  by 
  its 
  lower 
  density. 
  

   On 
  the 
  sawn 
  face 
  it 
  is 
  of 
  about 
  the 
  same 
  color 
  as 
  the 
  other. 
  The 
  tex- 
  

   ture 
  of 
  both 
  pieces 
  is 
  very 
  fine-grained, 
  indeed 
  quite 
  aphanitic. 
  The 
  

   material 
  shows 
  the 
  lack 
  of 
  toughness 
  which 
  is 
  characteristic 
  of 
  the 
  

   Middle 
  American 
  jades. 
  

  

  The 
  specific 
  gravity 
  of 
  the 
  smaller 
  piece 
  was 
  determined 
  by 
  me 
  as 
  

   2.934 
  at 
  19.4°, 
  giving 
  a 
  density 
  of 
  2.929; 
  while 
  Dr. 
  L. 
  H. 
  Adams 
  

   obtained 
  the 
  density 
  value 
  2.932 
  for 
  the 
  same 
  piece. 
  The 
  true 
  den- 
  

   sity 
  may 
  be 
  taken 
  as 
  2.930. 
  Adams 
  found 
  that 
  the 
  density 
  of 
  the 
  

   larger, 
  whitish 
  piece 
  is 
  2.756. 
  

  

  In 
  thin 
  section 
  the 
  jade 
  (of 
  piece 
  A) 
  is 
  seen 
  to 
  be 
  composed 
  largely 
  

   of 
  clear 
  albite 
  in 
  irregular 
  poikilitic 
  patches, 
  not 
  as 
  the 
  sharp 
  anhedral 
  

   grains 
  or 
  angular 
  interstitial 
  areas 
  which 
  are 
  most 
  commonly 
  seen 
  

   in 
  other 
  Middle 
  American 
  jades. 
  Through 
  this 
  albite 
  matrix 
  is 
  in- 
  

   terspersed, 
  not 
  uniformly, 
  considerable 
  pyroxene, 
  of 
  an 
  extremely 
  

   faint 
  brownish 
  color, 
  not 
  pleochroic. 
  Some 
  of 
  the 
  pyroxene 
  forms 
  

   rather 
  large 
  (0.5 
  mm. 
  long), 
  roughly 
  prismatic 
  grains; 
  much 
  of 
  it 
  

   is 
  in 
  small 
  (up 
  to 
  0.3 
  mm. 
  long), 
  sharp 
  prisms; 
  but 
  most 
  of 
  it 
  is 
  in 
  

   small 
  irregular 
  grains, 
  which 
  appear 
  to 
  be 
  due 
  to 
  crushing. 
  There 
  is 
  

   no 
  definite 
  general 
  orientation 
  of 
  the 
  pyroxene 
  crystals, 
  and 
  they 
  tend 
  

   to 
  be 
  felted 
  where 
  they 
  are 
  most 
  thickly 
  crowded. 
  No 
  other 
  minerals 
  

   were 
  seen 
  in 
  the 
  section. 
  

  

  Dr. 
  H. 
  E. 
  Merwin 
  kindly 
  determined 
  the 
  refractive 
  indices 
  of 
  the 
  

   pyroxene 
  and 
  found 
  the 
  values 
  : 
  a 
  = 
  1 
  . 
  665, 
  7 
  = 
  1- 
  693, 
  y 
  — 
  a 
  = 
  . 
  028 
  

   These 
  values 
  are 
  close 
  to 
  those 
  of 
  artificial 
  diopside 
  (CaMgSi^Oe): 
  

   a 
  = 
  1 
  .664, 
  7 
  = 
  1 
  .694, 
  7 
  — 
  a 
  = 
  0.030. 
  As 
  will 
  be 
  shown 
  presently 
  

   this 
  Copan 
  pyroxene 
  is 
  composed 
  of 
  about 
  71.5 
  per 
  cent 
  of 
  diopside 
  

   and 
  28.5 
  of 
  jadeite, 
  leaving 
  out 
  of 
  account 
  the 
  probable 
  presence 
  of 
  

   some 
  albite 
  in 
  solid 
  solution. 
  This 
  is 
  more 
  fully 
  discussed 
  in 
  the 
  forth- 
  

   coming 
  paper 
  mentioned 
  above. 
  

  

  A 
  chemical 
  analysis 
  was 
  made 
  of 
  a 
  portion 
  of 
  a 
  small 
  wedge 
  (weigh- 
  

   ing 
  about 
  3 
  grams) 
  which 
  was 
  sawn 
  out 
  of 
  the 
  end 
  of 
  (A) 
  the 
  smaller 
  

   and 
  fresher 
  piece. 
  The 
  analysis, 
  made 
  on 
  material 
  dried 
  at 
  110°, 
  

   gave 
  the 
  results 
  in 
  table 
  I. 
  

  

  The 
  analysis 
  of 
  the 
  Copan 
  jade 
  differs 
  widely 
  from 
  those 
  of 
  other 
  

   jades, 
  from 
  Chichen 
  Itza, 
  and 
  other 
  localities 
  in 
  Mexico, 
  and 
  Central 
  

  

  