﻿Lane 
  and 
  Skarpless 
  — 
  Notes 
  on 
  Michigan 
  Minerals. 
  505 
  

  

  schist 
  famous 
  for 
  its 
  large 
  pseudomorphs 
  of 
  chlorite 
  after 
  

   garnet. 
  The 
  most 
  abundant 
  impurities 
  are 
  ilmenite 
  and 
  mag- 
  

   netite. 
  Rutile, 
  quartz 
  and 
  sericite 
  are 
  much 
  less 
  common. 
  The 
  

   analyzed 
  material 
  was 
  examined 
  under 
  the 
  microscope 
  and, 
  

   though 
  not 
  absolutely 
  pure, 
  was 
  but 
  slightly 
  contaminated. 
  

   The 
  chloritoid 
  is 
  evidently 
  averse 
  to 
  enclosing 
  the 
  brown 
  mica 
  

   and 
  chlorite 
  which 
  also 
  occur 
  in 
  the 
  rock 
  and 
  they 
  occur 
  only 
  

   at 
  its 
  very 
  margins. 
  All 
  the 
  Michigan 
  chloritoids, 
  so 
  far 
  as 
  

   yet 
  known, 
  occur 
  in 
  altered 
  arkoses 
  or 
  similar 
  rocks, 
  in 
  one 
  

   case 
  both 
  in 
  the 
  cement 
  and 
  in 
  the 
  basic 
  and 
  acid 
  pebbles 
  of 
  a 
  

   conglomerate. 
  

  

  2. 
  Grunbeite 
  [L. 
  and 
  S.] 
  

  

  § 
  1. 
  There 
  is 
  a 
  peculiar 
  amphibole, 
  associated 
  with 
  certain 
  

   iron 
  ores 
  of 
  Lake 
  Superior, 
  which 
  has 
  been 
  called 
  both 
  actino- 
  

   lite 
  and 
  anthophyllite. 
  The 
  latter 
  name 
  is 
  due 
  to 
  Brush* 
  who 
  

   rightly 
  recognized 
  that 
  it 
  was 
  essentially 
  a 
  silicate 
  of 
  Fe 
  and 
  

   Mg. 
  He 
  was 
  followed 
  by 
  Brooks 
  and 
  Julien.f 
  On 
  the 
  other 
  

   hand 
  WichmanJ 
  and 
  Wadsworthg 
  rightly 
  recognized 
  that 
  

   it 
  was 
  not 
  orthorhombic, 
  and 
  referred 
  it 
  to 
  actinolite. 
  t 
  They 
  

   were 
  followed 
  by 
  Van 
  Hise,|| 
  while 
  C. 
  F. 
  Wright 
  in 
  some 
  of 
  

   his 
  work 
  called 
  the 
  rock 
  in 
  which 
  the 
  amphibole 
  occurs 
  an 
  

   anthophyllo-actinolite 
  schist. 
  

  

  § 
  2. 
  It 
  is 
  in 
  reality 
  a 
  ferro 
  magnesian 
  monoclinic 
  amphibole, 
  

   corresponding 
  closely 
  to 
  the 
  description 
  of 
  grunerite 
  given 
  by 
  

   LacroixT". 
  The 
  strong 
  refraction, 
  like 
  that 
  of 
  epidote, 
  is 
  no- 
  

   ticeable, 
  not 
  only 
  in 
  the 
  thin 
  section 
  but 
  in 
  the 
  hand 
  specimen, 
  

   which 
  has 
  in 
  consequence 
  a 
  peculiarly 
  high 
  silky 
  luster. 
  It 
  is 
  

   much 
  greater 
  than 
  that 
  of 
  common 
  blue 
  green 
  hornblende 
  or 
  

   actinolite, 
  but 
  less 
  than 
  that 
  of 
  garnet, 
  and 
  by 
  de 
  Chaulnes' 
  

   method 
  is 
  1*7. 
  The 
  bi-refraction 
  is 
  also 
  strong. 
  It 
  varies 
  in 
  

   specimens 
  from 
  different 
  localities, 
  but 
  is 
  always 
  stronger 
  than 
  

   that 
  of 
  actinolite 
  and 
  does 
  not 
  differ 
  markedly 
  from 
  that 
  of 
  

   the 
  talc 
  into 
  which 
  the 
  mineral 
  readily 
  changes, 
  so 
  that 
  y-a 
  is 
  

   always 
  >0*030. 
  

  

  The 
  polysynthetic 
  twinning 
  parallel 
  to 
  (100) 
  is 
  commonly 
  

   well 
  marked, 
  and 
  with 
  the 
  strong 
  optical 
  powers 
  distinguishes 
  

   it 
  at 
  a 
  glance 
  from 
  actinolite. 
  A 
  striation 
  parallel 
  to 
  (101), 
  

   which 
  should 
  be 
  more 
  properly 
  (001)*"*, 
  is 
  in 
  one 
  case 
  developed. 
  

   The 
  mineral 
  is 
  colorless 
  or 
  slightly 
  greenish 
  or 
  brownish, 
  but 
  

  

  * 
  Rep. 
  Mich. 
  Geol. 
  Survey, 
  I, 
  p. 
  114. 
  f 
  Idem, 
  11, 
  p. 
  24. 
  

  

  % 
  Report 
  Wis. 
  Geol. 
  Survey, 
  III, 
  p. 
  604. 
  

  

  § 
  Notes 
  on 
  the 
  Geol. 
  of 
  the 
  Iron 
  and 
  Copper 
  Districts 
  of 
  Lake 
  Superior, 
  p. 
  47, 
  

   et 
  passim. 
  

  

  || 
  This 
  Journal, 
  xli, 
  1891, 
  pp. 
  119 
  and 
  131. 
  

   ■jfLevy 
  et 
  Lacroix, 
  '• 
  Mineraux 
  des 
  Roches," 
  1889. 
  

   **G. 
  H. 
  Williams, 
  this 
  Journal, 
  xxxix, 
  1890, 
  p. 
  352. 
  

  

  