﻿300 
  Palache 
  — 
  Ejndote 
  and 
  Garnet 
  from 
  Idaho. 
  

  

  to 
  h, 
  and 
  are 
  generally 
  flattened 
  parallel 
  to 
  the 
  basal 
  plane 
  so 
  

   that 
  lense-shaped 
  cross-sections 
  are 
  common 
  ; 
  they 
  are 
  invari- 
  

   ably 
  implanted 
  on 
  an 
  end 
  of 
  the 
  orthoaxis, 
  b. 
  The 
  majority 
  of 
  

   the 
  crystals 
  are 
  terminated 
  simply 
  by 
  n 
  (111), 
  sometimes 
  

   together 
  wjth 
  h 
  (010), 
  and 
  in 
  the 
  orthodome 
  zone 
  show 
  c(OOl), 
  

   ^'(102), 
  r 
  (101), 
  and 
  a{lOO). 
  . 
  A 
  few 
  crystals, 
  however, 
  showed 
  

   a 
  much 
  richer 
  series 
  of 
  forms 
  as 
  seen 
  in 
  figs. 
  1 
  and 
  2, 
  which 
  

   are 
  orthographic 
  projections 
  on 
  the 
  clinopinacoid 
  and 
  repro- 
  

   duce 
  the 
  distortion 
  of 
  the 
  crystals. 
  

  

  Twinning 
  was 
  observed 
  on 
  several 
  crystals 
  according 
  to 
  the 
  

   usual 
  law: 
  twin 
  plane 
  a 
  {100). 
  In 
  one 
  crystal 
  the 
  twinning 
  

   was 
  repeated, 
  two 
  narrow 
  lamellae 
  intervening 
  between 
  the 
  

   two 
  principal 
  individuals. 
  

  

  Many 
  of 
  the 
  crystals 
  exhibit 
  a 
  strong 
  tendency 
  to 
  scale 
  off 
  in 
  

   concentric 
  shells 
  parallel 
  to 
  all 
  the 
  crystal 
  faces. 
  This 
  was 
  par- 
  

   ticularly 
  noticeable 
  in 
  the 
  crystals 
  figured 
  above, 
  even 
  the 
  smallest 
  

   faces 
  preserving 
  their 
  luster 
  and 
  permitting 
  good 
  measure- 
  

   ments 
  after 
  the 
  surface 
  layers 
  had 
  been 
  removed. 
  The 
  shelly 
  

   structure 
  sometimes 
  gives 
  rise 
  to 
  a 
  brilliant 
  iridescence 
  on 
  the 
  

   faces 
  of 
  the 
  crystal 
  and 
  is 
  generally 
  associated 
  with 
  a 
  bleaching 
  

   of 
  the 
  color, 
  presumably 
  due 
  to 
  surface 
  alteration. 
  

  

  Some 
  of 
  the 
  epidote 
  crystals 
  are 
  imbedded 
  in 
  quartz 
  of 
  later 
  

   growth, 
  the 
  latest 
  deposit 
  in 
  the 
  cavities. 
  A 
  single 
  specimen 
  

   from 
  the 
  Decorah 
  Mine 
  showed 
  such 
  imbedded 
  crystals 
  of 
  a 
  

   pale 
  green 
  epidote 
  which 
  were 
  exceptional 
  in 
  being 
  doubly 
  

   terminated. 
  

  

  The 
  epidote 
  is 
  in 
  places 
  largely 
  changed 
  to 
  a 
  scaly 
  chloritic 
  

   material 
  which 
  was 
  not 
  further 
  examined. 
  

  

  Garnet. 
  — 
  The 
  garnet 
  from 
  the 
  Peacock 
  Mine 
  is 
  almandite, 
  

   probably 
  the 
  same 
  as 
  that 
  analyzed 
  by 
  Melville^ 
  from 
  the 
  same 
  

   locality. 
  It 
  is 
  in 
  light 
  to 
  dark 
  brown, 
  completely 
  developed, 
  

   and 
  very 
  symmetrical 
  crystals 
  showing 
  the 
  forms 
  f/(101), 
  

   ^(211), 
  and 
  sometimes 
  5(321). 
  They 
  are 
  imbedded 
  in 
  glassy 
  

   copper-stained 
  quartz 
  from 
  which 
  they 
  easily 
  separate, 
  leaving 
  

   beautifully 
  sharp 
  casts. 
  

  

  A 
  second 
  type 
  of 
  garnet 
  is 
  found 
  in 
  the 
  Peacock 
  Mine 
  

   specimens. 
  Rough 
  crystals 
  an 
  inch 
  or 
  less 
  in 
  diameter 
  show 
  a 
  

   pronounced 
  dodecahedral 
  form, 
  the 
  edges 
  slightly 
  truncated 
  by 
  

   the 
  icositetrahedron 
  (211). 
  The 
  centers 
  of 
  the 
  crystals 
  are 
  of 
  a 
  

   dark 
  brown 
  garnet 
  substance; 
  but 
  the 
  exterior 
  is 
  unifonnly 
  

   coated 
  with 
  a 
  shell 
  of 
  clear 
  quartz 
  t}'"'" 
  in 
  thickness 
  conforming 
  

   in 
  minutest 
  detail 
  to 
  the 
  form 
  of 
  the 
  garnet 
  crystal. 
  A 
  thin 
  

   section 
  through 
  such 
  a 
  crystal 
  showed 
  that 
  the 
  quartz 
  in 
  one 
  of 
  

   these 
  shells 
  formed 
  but 
  a 
  single 
  crystal, 
  and 
  it 
  appears 
  to 
  repre- 
  

   sent 
  an 
  original 
  crystallization 
  controlled 
  in 
  the 
  disposition 
  of 
  

  

  * 
  Loc. 
  cit., 
  p. 
  138. 
  

  

  