﻿90 
  Thirtieth 
  Report 
  on 
  the 
  State 
  Museum. 
  

  

  There 
  are 
  several 
  varieties 
  of 
  labradorite 
  rock, 
  occurring 
  in 
  

   the 
  Norian 
  System 
  of 
  the 
  Adirondacks, 
  which 
  are 
  not 
  porphy- 
  

   ritic, 
  as 
  in 
  specimen 
  33, 
  which 
  is 
  apparently 
  massive 
  though 
  

   in 
  reality 
  crypto-crystalline. 
  On 
  a 
  fresh 
  surface 
  of 
  fracture 
  it 
  

   is 
  green, 
  no 
  diallage 
  in 
  separate 
  masses 
  being 
  visible, 
  but 
  on 
  a 
  

   weathered 
  surface 
  it 
  is 
  white 
  with 
  green 
  spots, 
  showing 
  that 
  in 
  

   fact 
  the 
  constituent 
  minerals 
  are 
  partially 
  segregated. 
  A 
  very 
  

   common 
  variety 
  in 
  certain 
  localities, 
  as 
  on 
  the 
  East 
  Branch 
  of 
  

   the 
  Ausable 
  River, 
  where 
  it 
  forms 
  hemlock- 
  covered 
  cliffs, 
  is 
  a 
  

   greasy 
  green 
  compact 
  labradorite, 
  with 
  some 
  admixed 
  diallage 
  

   and 
  garnet. 
  In 
  some 
  of 
  the 
  norian 
  porphyries, 
  the 
  smoky-grey 
  

   crystalline 
  portion 
  predominates 
  to 
  the 
  almost 
  entire 
  exclusion 
  

   of 
  the 
  feldspathic 
  matrix. 
  There 
  are 
  also 
  Pyroxenites, 
  with 
  

   but 
  little 
  feldspar 
  admixed, 
  and 
  in 
  which 
  the 
  pyroxene 
  is 
  

   sometimes 
  the 
  broadly 
  foliated 
  deep 
  green 
  variety 
  of 
  diallage, 
  

   and 
  at 
  others 
  is 
  faintly 
  or 
  strikingly 
  metallic 
  in 
  appearance. 
  

  

  In 
  a 
  few 
  localities, 
  rocks 
  composed 
  mostly 
  of 
  iron-garnet 
  

   with 
  some 
  hornblende, 
  have 
  been 
  encountered, 
  showing 
  a 
  pass- 
  

   age, 
  by 
  diminution 
  of 
  the 
  feldspathide, 
  of 
  norite 
  into 
  grenatite. 
  

  

  Besides 
  these 
  norites 
  proper, 
  there 
  are 
  many 
  intrusive 
  masses 
  

   composed 
  of 
  similar 
  materials, 
  but 
  in 
  which 
  the 
  constituents 
  

   are 
  not 
  stratified, 
  and 
  are 
  too 
  finely 
  divided 
  to 
  be 
  visible 
  to 
  the 
  

   naked 
  eye. 
  They 
  consist 
  chiefly 
  of 
  labradorite, 
  quartz, 
  pyrox- 
  

   ene 
  and 
  to 
  some 
  extent 
  hornblende, 
  magnetite 
  and 
  menaccanite. 
  

   Their 
  specific 
  gravity 
  is 
  about 
  2.9, 
  in 
  which 
  respect 
  they 
  stand 
  

   midway 
  between 
  the 
  extremes 
  of 
  the 
  Norian 
  series. 
  They 
  have 
  

   a 
  dark 
  grey 
  or 
  black 
  color, 
  with 
  a 
  smooth 
  and 
  sometimes 
  large 
  

   conchoidal 
  fracture, 
  and 
  in 
  some 
  localities, 
  as 
  in 
  specimen 
  66, 
  

   obtained 
  from 
  the 
  summit 
  of 
  Mt. 
  Marcy, 
  weather 
  unequally 
  

   into 
  a 
  pitted 
  surface 
  stained 
  by 
  yellow 
  oxide 
  of 
  iron. 
  

  

  The 
  pyroxenic 
  constituent 
  in 
  these 
  norites 
  contains 
  so 
  large 
  a 
  

   percentage 
  of 
  iron, 
  that 
  fusion 
  takes 
  place 
  very 
  readily 
  (F=3 
  

   to. 
  3) 
  with 
  a 
  production 
  of 
  a 
  black 
  globule, 
  generally 
  very 
  

   magnetic. 
  In 
  some 
  cases, 
  it 
  is 
  itself 
  magnetic, 
  from 
  included 
  

   magnetite. 
  

  

  