﻿500 
  Lane 
  and 
  Keller 
  — 
  Notes 
  on 
  Michigan 
  Minerals. 
  

  

  plates 
  several 
  centimeters 
  broad 
  and 
  up 
  to 
  4 
  mm 
  thick 
  at 
  the 
  

   Champion 
  Iron 
  Mine. 
  As 
  it 
  was 
  so 
  very 
  large, 
  not 
  very 
  im- 
  

   pure, 
  and 
  extremely 
  like 
  the 
  masonite 
  from 
  Natick 
  village, 
  

   Warwick 
  township, 
  R. 
  I., 
  it 
  seemed 
  worth 
  while 
  to 
  examine 
  it 
  

   both 
  chemically 
  and 
  optically. 
  The 
  results 
  have 
  brought 
  out 
  

   some 
  new 
  facts, 
  which 
  we 
  feel 
  justified 
  in 
  giving 
  now, 
  since 
  

   previous 
  data 
  have 
  been 
  neither 
  complete 
  nor 
  accordant, 
  even 
  

   though 
  we 
  hope 
  to 
  continue 
  our 
  investigations 
  into 
  the 
  chlori- 
  

   toid 
  group. 
  

  

  § 
  2. 
  We 
  may 
  summarize 
  our 
  results 
  as 
  follows. 
  All 
  the 
  

   Michigan 
  chloritoids, 
  as 
  well 
  as 
  the 
  masonite, 
  a 
  chloritoid 
  from 
  

   Pregratten, 
  one 
  from 
  Leeds, 
  Canada, 
  and 
  one 
  from 
  the 
  Apen- 
  

   nines, 
  appear 
  to 
  be 
  optically 
  the 
  same. 
  They 
  have 
  the 
  usual 
  

   trichroism 
  and 
  are 
  pronouncedly 
  triclinic. 
  The 
  axis 
  of 
  mean 
  

   elasticity 
  (/3) 
  is 
  inclined 
  some 
  20° 
  to 
  the 
  basis 
  (00V), 
  so 
  that 
  of 
  

   the 
  twin 
  lamellae 
  parallel 
  to 
  the 
  basis, 
  which 
  commonly 
  occur 
  

   in 
  three 
  sets, 
  that 
  one 
  has 
  the 
  greatest 
  angle 
  of 
  extinction 
  

   w 
  T 
  hich 
  is 
  most 
  blue 
  in 
  color. 
  The 
  horizontal 
  dispersion 
  is 
  

   strong. 
  Fig. 
  1 
  shows 
  the 
  lateral 
  cleavages, 
  and 
  a 
  stereographic 
  

   projection 
  on 
  the 
  basis 
  of 
  the 
  orientation 
  of 
  the 
  optical 
  axes. 
  

  

  All 
  the 
  chloritoids 
  that 
  we 
  have 
  tested, 
  i. 
  e. 
  those 
  from 
  

   Champion, 
  Pregratten 
  and 
  Natick 
  contain 
  constitutional 
  alkali. 
  

   In 
  this 
  respect, 
  as 
  otherwise 
  in 
  qualitative 
  composition 
  they 
  

   resemble 
  hornblendes 
  of 
  like 
  pleochroism. 
  Ottrelite 
  from 
  

   Gttrez 
  seems 
  to 
  be 
  optically 
  as 
  well 
  as 
  chemically 
  different, 
  

   and 
  less 
  pleochroic. 
  

  

  § 
  3. 
  The 
  detailed 
  description 
  of 
  

   the 
  Champion 
  chloritoid 
  is 
  as 
  fol- 
  

   lows 
  : 
  II. 
  6-5. 
  Sp. 
  G. 
  8-552. 
  Cleav- 
  

   age 
  basal, 
  perfect, 
  but 
  often 
  warped. 
  

   One 
  lateral 
  cleavage 
  if) 
  and 
  traces 
  

   of 
  two 
  or 
  three 
  others 
  can 
  be 
  seen. 
  

   The 
  color 
  is 
  dark 
  green, 
  almost 
  

   black 
  to 
  the 
  naked 
  eye. 
  It 
  is 
  

   decidedly 
  brittle. 
  

  

  The 
  measurements 
  given 
  below, 
  

   used 
  in 
  constructing 
  fig. 
  1, 
  were 
  

   mainly 
  made 
  with 
  the 
  microscope. 
  

   To 
  a 
  few 
  of 
  the 
  better 
  determined 
  

   ones 
  we 
  append 
  the 
  probable 
  error 
  

   [P. 
  E.]. 
  The 
  material 
  is 
  not 
  suited 
  

   for 
  exact 
  determinations. 
  

  

  The 
  / 
  bpt 
  = 
  the 
  /_ 
  between 
  the 
  

   traces 
  on 
  the 
  basis 
  of 
  the 
  two 
  lat- 
  

   eral 
  cleavages 
  nearest 
  to 
  the 
  two 
  directions 
  of 
  extinction. 
  

  

  