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  den 
  cooling 
  from 
  contact 
  with 
  the 
  rock, 
  assumed 
  the 
  more 
  vitreous 
  form 
  

   of 
  obsidian." 
  Report 
  on 
  the 
  Geol. 
  2d 
  JDist., 
  p. 
  184. 
  

  

  An 
  analysis 
  of 
  a 
  specimen 
  of 
  this 
  substance 
  gave, 
  silica, 
  55.50 
  ; 
  

   oxide 
  of 
  iron, 
  32.00 
  ; 
  lime, 
  with 
  a 
  minute 
  portion 
  of 
  alumina, 
  6.90 
  ; 
  

   magnesia, 
  4.62. 
  If 
  this 
  is 
  a 
  correct 
  view 
  of 
  its 
  composition, 
  it 
  differs 
  

   considerably 
  from 
  the 
  varieties 
  of 
  obsidian 
  heretofore 
  examined. 
  But 
  

   I 
  apprehend 
  that 
  its 
  chemical 
  character 
  will 
  be 
  found 
  liable 
  to 
  great 
  

   variations. 
  

  

  PYROPHYLLITE. 
  

   (Mineralogy 
  of 
  New- 
  York, 
  page 
  368.) 
  

   Well 
  characterized 
  specimens 
  of 
  this 
  beautiful 
  mineral 
  have 
  been 
  

   found 
  in 
  Phillipstown, 
  Putnam 
  county. 
  It 
  is 
  supposed 
  to 
  be 
  a 
  mechan- 
  

   ical 
  mixture, 
  consisting 
  of 
  greyish 
  green 
  foliated 
  scales, 
  looking 
  like 
  

   talc 
  or 
  mica 
  in 
  a 
  greyish 
  white, 
  mealy 
  base. 
  It 
  is, 
  however, 
  very 
  dis- 
  

   tinct 
  in 
  composition. 
  Mr. 
  J. 
  E. 
  Teschemacher 
  thinks 
  it 
  identical 
  with 
  

   vermiculite. 
  Proceed. 
  Bosl. 
  Nat. 
  Hist. 
  Soc'y, 
  1843. 
  

  

  (Mineralogy 
  of 
  New- 
  York, 
  page 
  369.) 
  

  

  This 
  mineral 
  is 
  exceedingly 
  abundant, 
  and 
  fine 
  specimens 
  have 
  been 
  

   found 
  in 
  various 
  parts 
  of 
  New-York, 
  many 
  of 
  them 
  of 
  great 
  beauty. 
  

   Attempts 
  have 
  been 
  made 
  to 
  arrange 
  the 
  multiplied 
  varieties 
  under 
  

   classes 
  or 
  groups, 
  but 
  these 
  have 
  not 
  been 
  entirely 
  successful. 
  They 
  

   differ 
  principally 
  in 
  their 
  optical 
  characters; 
  but 
  the 
  difficulty 
  which 
  at- 
  

   tends 
  their 
  division 
  founded 
  on 
  these 
  is, 
  that 
  the 
  chemical 
  composition 
  

   does 
  not 
  always 
  accord 
  with 
  them. 
  

  

  Since 
  the 
  publication 
  of 
  my 
  Mineralogy, 
  I 
  have 
  examined 
  several 
  of 
  

   the 
  New- 
  York 
  specimens 
  and 
  introduce 
  the 
  following 
  notices, 
  Avhich, 
  

   although 
  incomplete, 
  may 
  be 
  of 
  some 
  use 
  to 
  those 
  who 
  shall 
  hereafter 
  

   be 
  induced 
  to 
  take 
  up 
  the 
  investigation. 
  

  

  MARGAEITE. 
  

  

  Some 
  of 
  the 
  specimens 
  from 
  Orange 
  county, 
  often 
  ticketed 
  talc, 
  be- 
  

   long 
  to 
  this 
  species. 
  The 
  mineral 
  has 
  a 
  vitreous 
  lustre, 
  a 
  pale, 
  pearly 
  

   gray 
  color, 
  rather 
  brittle, 
  translucent 
  to 
  subtranslucent. 
  It 
  is 
  associated 
  

   with 
  chondrodite 
  and 
  pseudomorphs 
  of 
  hornblende. 
  It 
  exhibits 
  only 
  

   one 
  axis 
  of 
  double 
  refraction 
  and 
  fuses 
  per 
  se 
  into 
  a 
  white 
  enamel. 
  

   Similar 
  specimens 
  occur 
  in 
  the 
  town 
  of 
  Rossie, 
  St. 
  Lawrence 
  county. 
  

   I 
  have 
  not 
  analyzed 
  these 
  specimens. 
  

  

  