﻿Iwasaki 
  — 
  Orthoclase 
  Crystals 
  from 
  Shinano, 
  Japan. 
  157 
  

  

  Akt. 
  XYII. 
  — 
  On 
  the 
  Orthoclase 
  Crystals 
  from 
  Shinano^ 
  

   Japan 
  ; 
  by 
  C. 
  Iwasaki, 
  Kyoto, 
  Japan. 
  

  

  The 
  crystals 
  of 
  orthoclase 
  described 
  in 
  this 
  paper 
  were 
  

   obtained 
  by 
  me 
  from 
  Mr. 
  K. 
  Okiibo, 
  a 
  schoolmaster 
  in 
  Nozawa, 
  

   Minamisakiigori, 
  Shinano, 
  who 
  has 
  had 
  the 
  kindness 
  to 
  place 
  

   in 
  my 
  hands 
  some 
  fifty 
  specimens 
  from 
  a 
  locality 
  recently 
  dis- 
  

   covered 
  by 
  him 
  in 
  Moraiyama 
  of 
  the 
  same 
  district. 
  

  

  In 
  the 
  western 
  margin 
  of 
  the 
  geological 
  block 
  known 
  as 
  the 
  

   Chichibu 
  region, 
  where 
  the 
  geology 
  of 
  the 
  Japanese 
  Paleozoic 
  

   formation 
  has 
  been 
  studied 
  and 
  the 
  name 
  " 
  Chichibu 
  Group 
  " 
  

   has 
  been 
  given, 
  there 
  are 
  several 
  occurrences 
  of 
  quartz-diorite 
  

   as 
  dikes. 
  Through 
  some 
  of 
  them, 
  there 
  are 
  mineral 
  veins 
  a 
  

   footr 
  in 
  width 
  formed, 
  and 
  the 
  orthoclase 
  crystals 
  are 
  found 
  in 
  

   them 
  mixed 
  with 
  quartz. 
  

  

  The 
  orthoclase 
  crystals 
  are 
  all 
  elongated 
  in 
  the 
  direction 
  of 
  

   the 
  clino-axis; 
  one 
  end 
  being 
  always 
  broken. 
  They 
  are 
  of 
  

   moderate 
  size, 
  and 
  measure 
  one 
  and 
  a 
  half 
  inches 
  in 
  the 
  longest 
  

   diameter. 
  They 
  are 
  brownish 
  white 
  in 
  color, 
  often 
  with 
  thin 
  

   coating 
  of 
  the 
  brown 
  earth. 
  Tlie 
  clinopinacoid 
  (010) 
  is 
  com- 
  

   paratively 
  clean 
  and 
  lustrous, 
  and 
  striations 
  parallel 
  to 
  the 
  

   vertical 
  axis 
  are 
  seen 
  on 
  it. 
  The 
  basal 
  face 
  (001) 
  is 
  usually 
  dis- 
  

   colored 
  and 
  the 
  cleavage 
  along 
  it 
  is 
  most 
  perfect. 
  All 
  faces 
  

   are 
  so 
  dull 
  that 
  the 
  facial 
  angles 
  can 
  only 
  be 
  measured 
  approxi- 
  

   mately 
  by 
  the 
  contact 
  o-oniometer. 
  Six 
  crystal 
  faces, 
  (010), 
  

   (001),\llO), 
  (130), 
  (I01),"i>01), 
  have 
  been 
  identified. 
  

  

  The 
  crystals 
  are 
  nearly 
  always 
  twinned 
  after 
  the 
  Baveno 
  

   type 
  but 
  of 
  different 
  types. 
  They 
  may 
  be 
  divided 
  into 
  the 
  

   four 
  classes 
  mentioned 
  below. 
  

  

  (1) 
  Simple 
  crystals 
  (tig. 
  1). 
  — 
  The 
  simple 
  crystals 
  are 
  most 
  

   rarely 
  met 
  with. 
  Only 
  two 
  were 
  found 
  among 
  fifty 
  specimens, 
  

   and, 
  even 
  in 
  them, 
  the 
  twinning 
  traces 
  are 
  seen 
  in 
  their 
  margin. 
  

   The 
  crystal 
  habitus 
  is 
  as 
  usual. 
  

  

  (2) 
  Tvnn 
  crystals 
  of 
  the 
  Baveno 
  tyj)& 
  (figs. 
  2 
  and 
  3). 
  — 
  

   All 
  crystals 
  are 
  drawn 
  in 
  the 
  orthographic 
  projection 
  toward 
  

   the 
  clino 
  axis. 
  Fig. 
  1. 
  Simple 
  crystal 
  ; 
  figs. 
  2, 
  3, 
  twin 
  crys- 
  

   tals 
  of 
  the 
  Baveno 
  type 
  (110) 
  and 
  (130) 
  are 
  more 
  developed 
  in 
  

   3. 
  Figs. 
  4-8, 
  Baveno 
  trillings 
  : 
  4, 
  normal 
  case 
  ; 
  in 
  5 
  and 
  6, 
  

   the 
  groove 
  between 
  A 
  and 
  C, 
  proceeds 
  into 
  B 
  ; 
  in 
  7 
  the 
  prism 
  

   is 
  absent 
  ; 
  in 
  8, 
  the 
  faces 
  are 
  unequally 
  developed 
  on 
  both 
  

   sides 
  of 
  the 
  groove. 
  Fig. 
  9. 
  Baveno 
  fourling. 
  The 
  simple 
  

   crystals 
  are 
  frequently 
  twinned 
  after 
  the 
  Baveno 
  type, 
  a 
  diago- 
  

   nally 
  truncated 
  prism 
  being 
  the 
  result. 
  Among 
  the_terminal 
  

   faces 
  (110) 
  plays 
  the 
  most 
  important 
  role, 
  (101), 
  (201) 
  and 
  

   sometimes 
  (_130) 
  being 
  only 
  seen 
  in 
  a 
  corner 
  or 
  on 
  the 
  edges, 
  

   but 
  rarely 
  (101) 
  and 
  (501) 
  "^are 
  highly 
  developed 
  and 
  (110) 
  is 
  

   depressed 
  in 
  one 
  side 
  as 
  shown 
  in 
  fig. 
  3. 
  

  

  