﻿326 
  E. 
  V. 
  Shannon 
  — 
  Crystals 
  of 
  Pyromorjphite. 
  

  

  Description. 
  — 
  The 
  mineral 
  occurs 
  commonly 
  in 
  crusts 
  of 
  

   minute 
  crystals 
  coating 
  cracks 
  in 
  galena 
  or 
  as 
  larger 
  individuals 
  

   in 
  cracks 
  in 
  quartzite. 
  The 
  color 
  ranges 
  from 
  faintly 
  pink 
  to 
  

   colorless 
  in 
  the 
  smallest 
  crystals 
  to 
  quite 
  deep 
  grayish 
  violet 
  in 
  

   some 
  of 
  the 
  larger 
  ones. 
  In 
  size 
  they 
  range 
  from 
  microscopic 
  

   to 
  an 
  occasional 
  length 
  of 
  l*5 
  cm 
  , 
  the 
  larger 
  being 
  those 
  in 
  the 
  

   wall-rocks. 
  Those 
  over 
  5 
  mm 
  in 
  length 
  are 
  commonly 
  nearly 
  

   opaque 
  with 
  curved 
  prism 
  faces 
  and 
  brush-like 
  terminations. 
  

   The 
  luster 
  in 
  the 
  smaller 
  crystals 
  is 
  adamantine 
  while 
  that 
  of 
  

   the 
  larger 
  opaque 
  crystals 
  is 
  resinous. 
  Quite 
  commonly 
  the 
  

   crystals 
  are 
  attached 
  by 
  a 
  prism 
  face 
  and 
  are 
  then 
  doubly 
  

   terminated, 
  the 
  form 
  being 
  essentially 
  like 
  the 
  accompanying 
  

   figure 
  1 
  with 
  the 
  length 
  several 
  times 
  the 
  diameter. 
  At 
  times 
  

  

  Fig. 
  1. 
  

  

  Fig. 
  2. 
  

  

  x 
  *< 
  

  

  ■■tu 
  

  

  To, 
  

  

  Til 
  

  

  a. 
  

  

  -m- 
  

  

  m 
  

  

  & 
  

  

  these 
  small 
  prisms 
  greatly 
  resemble 
  quartz 
  crystals, 
  the 
  resem- 
  

   blance 
  being 
  heightened 
  by 
  an 
  unequal 
  development 
  of 
  the 
  

   pyramid 
  faces 
  which 
  gives 
  them 
  a 
  rhombic 
  aspect. 
  As 
  no 
  

   suitable 
  material 
  was 
  at 
  hand 
  when 
  it 
  was 
  decided 
  to 
  describe 
  

   the 
  occurrence, 
  a 
  specimen 
  of 
  the 
  type 
  material 
  was 
  borrowed 
  

   from 
  Col. 
  W. 
  A. 
  Koebling. 
  The 
  crystals 
  measured 
  were 
  taken 
  

   from 
  this 
  specimen. 
  While 
  promising 
  in 
  appearance 
  these 
  

   crystals 
  are 
  somewhat 
  dull 
  and 
  give 
  very 
  poor 
  signals. 
  The 
  

   forms 
  noted 
  were 
  the 
  pyramid 
  x 
  (1011) 
  and 
  the 
  prism 
  in 
  (1010). 
  

   JSfo 
  other 
  planes 
  have 
  been 
  observed. 
  The 
  best 
  crystal, 
  

   measured 
  on 
  the 
  reflecting 
  goniometer, 
  gave 
  the 
  value 
  x^x"'= 
  

   80°50'. 
  This 
  is 
  sufficiently 
  close 
  to 
  the 
  calculated 
  angle 
  (80°44') 
  

   to 
  identify 
  the 
  form. 
  

  

  The 
  presence 
  of 
  lead, 
  chlorine, 
  and 
  phosphoric 
  acid 
  were 
  

   proven 
  by 
  qualitative 
  methods, 
  as 
  were 
  the 
  absence 
  of 
  vanadium, 
  

   calcium 
  and 
  arsenic. 
  Col. 
  Roebling 
  reports 
  that 
  a 
  preliminary 
  

  

  