﻿PARX 
  3. 
  

  

  ECONOMIC 
  GEOLOGY 
  

   Building 
  Stone 
  " 
  

  

  GRANITIC 
  ROCKS 
  

   Granite, 
  Gneiss, 
  Syenite, 
  Trap 
  and 
  Norite 
  

  

  Granite. 
  Typical 
  granite 
  is 
  a 
  crystalline, 
  granular 
  mixture 
  of 
  

   a 
  feldspar, 
  quartz 
  and 
  hornblende. 
  In 
  addition 
  to 
  these 
  essential 
  

   constituents, 
  one 
  or 
  more 
  accessory 
  minerals 
  may 
  be 
  present. 
  

   The 
  more 
  common 
  are 
  the 
  micas, 
  muscovite 
  and 
  biotite, 
  garnet, 
  

   tourmaline, 
  magnetite 
  and 
  pyrite. 
  The 
  character 
  of 
  the 
  rock 
  is 
  

   often 
  determined 
  by 
  the 
  presence 
  of 
  these 
  accessory 
  constituents 
  

   in 
  quantity, 
  as 
  in 
  some 
  cases 
  the 
  hornblende 
  is 
  entirely 
  replaced 
  

   by 
  mica. 
  '^ 
  

  

  The 
  chemical 
  composition 
  also 
  varies 
  from 
  that 
  of 
  the 
  average 
  

   or 
  typical 
  kind. 
  The 
  mineralogical 
  differences 
  mark 
  the 
  varie- 
  

   ties, 
  thus 
  there 
  are: 
  hornblende 
  granite, 
  biotite 
  granite, 
  tourma- 
  

   line 
  granite, 
  etc. 
  

  

  The 
  texture 
  of 
  granites 
  is 
  determined 
  by 
  the 
  aggregated 
  miner- 
  

   als 
  entering 
  into 
  their 
  composition. 
  It 
  varies 
  from 
  coarse-crystal- 
  

   line, 
  in 
  which 
  the 
  individual 
  crystals 
  may 
  be 
  an 
  inch 
  or 
  more 
  in 
  

   length, 
  to 
  fine-crystalline 
  and 
  aphanitic, 
  w^herein 
  the 
  minerals 
  

   are 
  hardly 
  visible 
  to 
  the 
  eye. 
  In 
  consequence 
  of 
  the 
  wide 
  varia- 
  

   tion 
  due 
  to 
  the 
  mode 
  of 
  arrangement 
  of 
  the 
  mineral 
  constituents, 
  

   there 
  is 
  an 
  equally 
  great 
  variety 
  noticeable 
  in 
  the 
  texture. 
  

  

  The 
  color 
  also 
  is 
  dependent 
  upon 
  the 
  minerals. 
  As 
  feldspar 
  

   is 
  the 
  predominant 
  constituent 
  it 
  gives 
  character 
  to 
  the 
  mass, 
  

   and 
  the 
  red 
  varieties 
  owe 
  their 
  color 
  to 
  the 
  red 
  or 
  pink 
  feldspars 
  

   in 
  them, 
  as 
  in 
  the 
  case 
  of 
  the 
  granite 
  of 
  Grindstone 
  Island 
  in 
  

   the 
  St 
  Lawrence. 
  The 
  shades 
  of 
  gray 
  are 
  due 
  to 
  the 
  varying 
  

  

  a 
  This 
  chapter 
  on 
  building 
  stone 
  is 
  abridged 
  with 
  alterations 
  and 
  additions 
  from 
  

   Bulletin 
  No. 
  10 
  of 
  the 
  New 
  York 
  State 
  Museum, 
  by 
  John 
  C. 
  Smock. 
  

  

  