﻿408 
  L. 
  V. 
  Pirsson 
  — 
  Mineralogical 
  Notes. 
  

  

  the 
  twinning 
  axis 
  a 
  normal 
  to 
  100 
  and 
  the 
  following 
  simple 
  

   forms 
  are 
  present, 
  m, 
  7", 
  110; 
  b, 
  i\ 
  010; 
  

   Z, 
  -1, 
  111; 
  and 
  e, 
  -J-£, 
  103. 
  Since 
  the 
  or- 
  

   thodome 
  %-i, 
  lacks 
  only 
  about 
  two 
  degrees 
  

   of 
  forming 
  a 
  right 
  angle 
  with 
  the 
  orthopin- 
  

   acoid, 
  the 
  two 
  domes 
  in 
  twin 
  position 
  prac- 
  

   tically 
  present 
  the 
  appearance 
  of 
  a 
  basal 
  

   plane 
  and 
  the 
  whole 
  crystal 
  that 
  of 
  hemi- 
  

   morphic 
  orthorhombic 
  rather 
  than 
  of 
  mon- 
  

   oclinic 
  symmetry. 
  This 
  pseudo-basal 
  plane 
  is 
  rough 
  and 
  oscil- 
  

   latory 
  and 
  the 
  very 
  slight 
  salient 
  angle 
  cannot 
  be 
  detected. 
  

   The 
  crystals 
  are 
  of 
  good 
  size 
  and 
  very 
  symmetrical 
  except 
  at 
  

   the 
  end 
  where 
  the 
  twin 
  pyramids 
  are 
  ; 
  they 
  are 
  attached 
  by 
  

   this 
  point 
  and 
  are 
  as 
  a 
  consequence 
  broken 
  and 
  disturbed 
  at 
  

   this 
  place. 
  

  

  4. 
  Pennine. 
  — 
  The 
  crystal 
  form 
  and 
  optical 
  properties 
  of 
  the 
  

   violet 
  chrome 
  pennine 
  or 
  kammererite 
  from 
  Texas, 
  Penn., 
  

   were 
  originally 
  described 
  by 
  Cooke* 
  from 
  specimens 
  from 
  the 
  

   cabinet 
  of 
  Prof. 
  Brush. 
  At 
  the 
  request 
  of 
  Prof. 
  E. 
  S. 
  Dana 
  I 
  

   have 
  recently 
  studied 
  the 
  suite 
  of 
  specimens 
  in 
  Prof. 
  Brush's 
  

   collection 
  from 
  this 
  locality 
  and 
  thanks 
  to 
  the 
  present 
  perfec- 
  

   tion 
  of 
  apparatus 
  for 
  cry 
  stall 
  ographic 
  investigation, 
  I 
  have 
  

   been 
  able 
  to 
  make 
  out 
  several 
  forms 
  observed 
  by 
  Prof. 
  Cooke 
  

   but 
  which 
  he 
  was 
  not 
  then 
  able 
  to 
  determine. 
  The 
  forms 
  ob- 
  

   served 
  on 
  these 
  crystals 
  are 
  as 
  follows 
  : 
  

  

  O, 
  0001: 
  R, 
  1011; 
  y, 
  \, 
  2025; 
  <p, 
  f 
  3 
  , 
  4*0'4'13 
  ; 
  z, 
  £, 
  1013; 
  p, 
  £-2, 
  1124 
  

   X, 
  1-2, 
  1122. 
  

  

  The 
  last 
  three 
  are 
  new. 
  The 
  habit 
  is 
  shown 
  in 
  figs. 
  6 
  and 
  7. 
  

   Fig. 
  6 
  is 
  very 
  similar 
  to 
  that 
  given 
  by 
  Cooke, 
  omitting 
  the 
  

   pyramids 
  of 
  the 
  second 
  order. 
  As 
  observed 
  by 
  him 
  the 
  crys- 
  

   tals 
  are 
  generally 
  twins. 
  The 
  planes 
  forming 
  the 
  re-entrant 
  

   angle 
  are 
  nearly 
  always 
  more 
  or 
  less 
  striated, 
  moreover 
  this 
  re- 
  

   entrant 
  angle 
  is, 
  so 
  far 
  as 
  observed, 
  invariably 
  formed 
  by 
  the 
  

   unit 
  rhombohedron 
  R 
  (1011). 
  Fig. 
  7 
  shows 
  a 
  case 
  where 
  there 
  

   was 
  practically 
  no 
  striation 
  and 
  the 
  angle 
  could 
  be 
  measured. 
  

   The 
  presence 
  of 
  pyramids 
  of 
  the 
  second 
  order 
  is 
  a 
  noteworthy 
  

   characteristic, 
  on 
  no 
  crystal 
  out 
  of 
  a 
  large 
  number 
  was 
  it 
  ever 
  

   wanting. 
  With 
  one 
  or 
  two 
  exceptions, 
  on 
  very 
  small 
  crystals, 
  

   they 
  were 
  invariably 
  striated 
  as 
  shown 
  in 
  fig. 
  7. 
  These 
  stria- 
  

   tions 
  all 
  lie 
  in 
  one 
  zone, 
  and 
  this 
  having 
  been 
  determined, 
  it 
  

   was 
  possible 
  to 
  measure 
  from 
  the 
  base 
  along 
  this 
  zone, 
  the 
  re- 
  

   flections 
  of 
  various 
  pyramids 
  which 
  stood 
  out 
  in 
  the 
  band 
  of 
  

   light 
  connecting 
  them. 
  

  

  'ln__this 
  way 
  the 
  presence 
  of 
  f2 
  (1126), 
  f-2 
  (2245), 
  T 
  %-2 
  

   (9-9-18-20) 
  and 
  f 
  2 
  (7'7*14-8) 
  was 
  determined 
  by 
  moderately 
  

  

  * 
  This 
  Journal, 
  vol. 
  xliv, 
  pp. 
  201, 
  1867. 
  

  

  