﻿40 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  The 
  whole 
  range 
  in 
  mineralogical 
  composition 
  is 
  brought 
  out 
  in 
  

   the 
  following 
  table 
  : 
  

  

  Table 
  9 
  

   Mineralogical 
  composition 
  of 
  the 
  diabase 
  

  

  

  Slide 
  

  

  no. 
  

  

  Andesine 
  

  

  to 
  labra- 
  

  

  dorite 
  

  

  Augite 
  

  

  Biotite 
  

  

  Ilmenite 
  

  

  

  Glassy 
  

  

  ground 
  

  

  mass 
  

  

  Quartz 
  

  

  Apa- 
  

   tite 
  

  

  I 
  

  

  8 
  

  

  48 
  

  

  7 
  

  

  10 
  

   9 
  

  

  47 
  

  

  55 
  

  

  55 
  

  

  5 
  

   55 
  

  

  25 
  22.5 
  

  

  37 
  

  

  4 
  

   6 
  

  

  5 
  

  

  many 
  

  

  specks 
  

  

  5 
  

  

  1 
  

  

  little 
  

   little 
  

  

  85 
  

   25 
  

  

  little 
  

   2 
  

  

  little 
  

  

  little 
  

  

  little 
  

  

  little 
  

  

  2 
  

  

  Mostly 
  chlorite 
  

   40 
  

  

  3 
  

  

  4 
  

   5 
  

  

  Mostly 
  

  

  5 
  

   14 
  

  

  chlorite. 
  

  

  The 
  remarkable 
  similarity 
  in 
  composition 
  is 
  a 
  striking 
  feature. 
  

   Nos. 
  1, 
  2, 
  and 
  3 
  are 
  typical 
  noncrystalline 
  diabases 
  from 
  widely 
  

   separated 
  dikes. 
  Nos. 
  4 
  and 
  5 
  represent 
  finer 
  grained 
  or 
  border 
  

   phases 
  and 
  have 
  more 
  or 
  less 
  glassy 
  ground 
  mass. 
  No. 
  5 
  presents 
  

   a 
  striking 
  appearance 
  under 
  the 
  microscope 
  because 
  the 
  feldspar 
  

   crystals 
  which 
  are 
  incipient 
  and 
  almost 
  indeterminate 
  tend 
  toward 
  

   sheaf 
  like 
  bundles 
  (see 
  plate 
  6, 
  lower 
  figure). 
  

  

  Number 
  1 
  of 
  table 
  9, 
  which 
  may 
  be 
  regarded 
  as 
  typical 
  of 
  all 
  the 
  

   diabases, 
  is 
  from 
  the 
  large 
  dike 
  (above 
  described) 
  at 
  the 
  base 
  of 
  

   Heath 
  mountain. 
  The 
  fine 
  to 
  medium 
  grained 
  rock 
  shows 
  an 
  excel- 
  

   lent 
  diabasic 
  texture 
  visible 
  even 
  to 
  the 
  naked 
  eye. 
  Judging 
  by 
  the 
  

   extinction 
  angles, 
  the 
  broad 
  laths 
  .of 
  somewhat 
  decomposed 
  plagio- 
  

   clase 
  range 
  from 
  andesine 
  to 
  labradorite 
  in 
  composition. 
  Pale 
  red- 
  

   dish 
  brown 
  augite, 
  in 
  stout 
  prisms, 
  shows 
  a 
  very 
  faint 
  pleochroism. 
  

   It 
  exhibits 
  good 
  cleavage 
  and 
  sometimes 
  good 
  crystal 
  boundaries. 
  

   The 
  biotite 
  is 
  much 
  changed 
  to 
  chlorite 
  and 
  stained 
  with 
  black 
  iron 
  

   oxid. 
  The 
  ilmenite 
  often 
  shows 
  transition 
  to 
  leucoxene. 
  Apatite 
  

   occurs 
  in 
  tiny 
  needles, 
  and 
  pyrite 
  and 
  quartz 
  in 
  small 
  irregular 
  

   grains, 
  the 
  latter 
  being 
  probably 
  of 
  secondary 
  origin. 
  

  

  Chemical 
  composition, 
  norm, 
  and 
  mode 
  

   The 
  diabase 
  from 
  the 
  dike 
  at 
  the 
  western 
  base 
  of 
  Heath 
  moun- 
  

   tain 
  has 
  been 
  analyzed 
  for 
  the 
  writer 
  by 
  Prof. 
  E. 
  W. 
  Morley. 
  

  

  