﻿170 
  

  

  Ford 
  and 
  Bradley 
  — 
  Pyroxmangite. 
  

  

  is 
  amber, 
  yellowish 
  brown, 
  reddish 
  brown 
  to 
  dark 
  brown, 
  the 
  

   darker 
  colors 
  predominating. 
  It 
  is 
  translucent 
  to 
  opaque. 
  It 
  

   fuses 
  quietly 
  about 
  3 
  to 
  a 
  black 
  and 
  magnetic 
  globule. 
  It 
  gives 
  

   the 
  manganese 
  color 
  reactions 
  with 
  the 
  fluxes. 
  It 
  is 
  insoluble 
  

   in 
  acids. 
  

  

  The 
  mineral 
  was 
  poorly 
  adapted 
  for 
  optical 
  observations 
  and 
  

   measurements, 
  but 
  the 
  following 
  facts 
  were 
  established. 
  It 
  is 
  

   biaxial 
  and 
  optically 
  positive. 
  A 
  section 
  cut 
  in 
  the 
  prism 
  zone 
  

   and 
  making 
  an 
  angle 
  of 
  44° 
  5' 
  with 
  each 
  of 
  the 
  cleavages 
  

  

  Fig. 
  1. 
  

  

  qi°50 
  

  

  vv°s 
  

  

  Artificial 
  

   T/o7?e 
  

  

  Artificial 
  

   Thne 
  

  

  (i. 
  e., 
  a 
  section 
  near 
  the 
  position 
  of 
  the 
  parting 
  plane, 
  b 
  (010)), 
  

   showed 
  an 
  extinction 
  angle 
  measured 
  to 
  the 
  trace 
  of 
  the 
  pris- 
  

   matic 
  cleavage 
  of 
  about 
  5°. 
  A 
  section 
  cut 
  parallel 
  to 
  the 
  

   parting 
  plane 
  showed 
  an 
  extinction 
  practically 
  parallel 
  to 
  the 
  

   lines 
  of 
  cleavage. 
  The 
  axial 
  plane 
  is 
  normal 
  to 
  the 
  parting 
  

   plane, 
  b 
  (010). 
  A 
  section 
  cut 
  in 
  the 
  prism 
  zone 
  at 
  right 
  angles 
  

   to 
  the 
  first 
  section 
  mentioned 
  above 
  and 
  making 
  an 
  angle 
  of 
  

   45° 
  55' 
  with 
  both 
  cleavage 
  planes, 
  showed 
  an 
  extinction 
  angle 
  

   of 
  approximately 
  45° 
  with. 
  the 
  trace 
  of 
  the 
  cleavage. 
  The 
  

   refractive 
  index 
  was 
  measured 
  by 
  immersion 
  of 
  fragments 
  of 
  

   the 
  mineral 
  in 
  high 
  refracting 
  liquids 
  and 
  by 
  applying 
  the 
  

   Becke 
  test 
  to 
  them 
  it 
  was 
  found 
  to 
  range 
  between 
  1*75 
  and 
  

   1*76. 
  The 
  optical 
  angle 
  was 
  measured 
  under 
  the 
  microscop 
  

  

  