﻿Ford 
  and 
  Bradley 
  — 
  Pyroxmangite. 
  169 
  

  

  Art. 
  XX. 
  — 
  Pyroxmangite, 
  a 
  New 
  Member 
  of 
  the 
  Pyroxene 
  

   Group 
  and 
  its 
  Alteration 
  Product, 
  Sleemmatite 
  ; 
  by 
  W. 
  E. 
  

   Ford 
  and 
  W. 
  M. 
  Bradley. 
  

  

  The 
  minerals 
  to 
  be 
  described 
  in 
  this 
  paper 
  were 
  found 
  four 
  

   and 
  one-half 
  miles 
  east 
  of 
  Iva, 
  Anderson 
  county, 
  South 
  Caro- 
  

   lina, 
  by 
  Mr. 
  George 
  Letchworth 
  English, 
  of 
  Shelby, 
  1ST. 
  C, 
  

   who 
  kindly 
  submitted 
  them 
  to 
  the 
  Mineralogical 
  Laboratory 
  of 
  

   the 
  Sheffield 
  Scientific 
  School 
  for 
  investigation. 
  

  

  On 
  preliminary 
  examination 
  one 
  of 
  them 
  proved 
  to 
  be 
  essen- 
  

   tially 
  a 
  silicate 
  of 
  manganese 
  and 
  ferrous 
  iron 
  with 
  the 
  general 
  

   characteristics 
  of 
  a 
  pyroxene. 
  It 
  was 
  at 
  first 
  thought 
  to 
  be 
  a 
  

   scheff 
  erite, 
  but 
  further 
  study 
  proved 
  it 
  to 
  be 
  quite 
  distinct 
  from 
  

   that 
  species. 
  It 
  differs 
  from 
  schefferite 
  in 
  that 
  it 
  contains 
  only 
  

   a 
  little 
  lime, 
  no 
  magnesia, 
  and 
  much 
  higher 
  percentages 
  of 
  iron 
  

   and 
  manganese 
  oxides. 
  Further, 
  the 
  crystallographic 
  and 
  opti- 
  

   cal 
  properties 
  show 
  that 
  it 
  is 
  triclinic. 
  As 
  far 
  as 
  the 
  analysis 
  

   goes 
  it 
  might 
  be 
  a 
  highly 
  ferriferous 
  rhodonite, 
  for 
  the 
  analysis 
  

   given 
  below 
  does 
  not 
  differ 
  materially 
  from 
  that 
  of 
  a 
  rhodonite 
  

   from 
  Vester 
  Silfberg 
  given 
  by 
  Weibull 
  and 
  quoted 
  by 
  Dana 
  

   as 
  analysis 
  9, 
  page 
  380, 
  of 
  the 
  System 
  of 
  Mineralogy. 
  The 
  

   crystallographic 
  and 
  optical 
  characters 
  of 
  the 
  two 
  minerals 
  do 
  

   not, 
  however, 
  agree 
  as 
  shown 
  below. 
  The 
  cleavage 
  angle 
  of 
  

   pyroxmangite 
  differs 
  from 
  that 
  of 
  rhodonite 
  by 
  about 
  half 
  a 
  

   degree. 
  The 
  extinction 
  directions 
  of 
  the 
  two 
  minerals 
  differ 
  by 
  

   angles 
  ranging 
  from 
  10 
  to 
  13 
  degrees. 
  The 
  axial 
  angle 
  of 
  

   pyroxmangite 
  is 
  small 
  and 
  its 
  optical 
  character 
  is 
  positive, 
  

   while 
  the 
  axial 
  angle 
  of 
  rhodonite 
  varies 
  between 
  72° 
  and 
  76° 
  

   and 
  it 
  is 
  optically 
  negative. 
  Pyroxmangite 
  differs 
  markedly 
  in 
  

   its 
  composition 
  from 
  that 
  of 
  babingtonite. 
  The 
  conclusion, 
  

   therefore, 
  is 
  that 
  it 
  is 
  a 
  new 
  member 
  of 
  the 
  Pyroxene 
  Group, 
  

   belonging 
  in 
  the 
  triclinic 
  section. 
  

  

  It 
  was 
  found 
  only 
  in 
  cleavable 
  masses, 
  no 
  indication 
  of 
  

   crystal 
  forms 
  being 
  observed. 
  It 
  is 
  triclinic 
  as 
  proved 
  by 
  the 
  

   character 
  of 
  its 
  cleavages 
  and 
  its 
  optical 
  structure. 
  It 
  shows 
  

   two 
  cleavages, 
  one 
  of 
  which 
  is 
  quite 
  good 
  while 
  the 
  other 
  is 
  

   rather 
  poor. 
  The 
  difference 
  in 
  the 
  quality 
  of 
  the 
  two 
  cleav- 
  

   ages 
  is 
  very 
  distinct. 
  The 
  average 
  of 
  a 
  number 
  of 
  measure- 
  

   ments 
  gave 
  the 
  angle 
  between 
  the 
  two 
  cleavage 
  planes 
  as 
  91° 
  

   50'. 
  A 
  parting 
  plane, 
  occupying 
  the 
  position 
  of 
  the 
  crystal 
  

   face 
  b 
  (010) 
  was 
  occasionally 
  to 
  be 
  observed. 
  The 
  angle 
  

   between 
  this 
  plane 
  and 
  the 
  better 
  cleavage 
  was 
  measured 
  as 
  

   45° 
  14', 
  giving 
  the 
  angle 
  between 
  it 
  and 
  the 
  poorer 
  cleavage 
  

   as 
  42° 
  56'. 
  

  

  The 
  hardness 
  is 
  5*5-6. 
  The 
  specific 
  gravity 
  was 
  determined 
  

   as 
  3*80. 
  The 
  1 
  Lister 
  is 
  vitreous, 
  inclining 
  to 
  resinous. 
  Its 
  color 
  

  

  