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  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Minerals 
  

  

  Minerals 
  are 
  classified 
  by 
  their 
  chemical 
  composition 
  and 
  by 
  

   the 
  geometric 
  forms 
  which 
  they 
  assume 
  in 
  crystallization, 
  each 
  

   mineral 
  having 
  a 
  certain 
  range 
  of 
  forms 
  from 
  which 
  it 
  cannot 
  

   depart.^* 
  

  

  These 
  forms 
  are 
  grouped 
  in 
  six 
  systems 
  named 
  as 
  follows: 
  

   Isometric, 
  Tetragonal, 
  Hexagonal, 
  Orthorhombic, 
  Monoclinic 
  and 
  

   Triclinic. 
  These 
  systems 
  are 
  characterized 
  by 
  and 
  named 
  in 
  ac- 
  

   cordance 
  with 
  the 
  number 
  and 
  relation 
  of 
  the 
  axes 
  about 
  which 
  

   the 
  external 
  geometric 
  faces 
  are 
  developed. 
  In 
  physical 
  relation 
  

   with 
  these 
  axes 
  are 
  distinct 
  optical 
  properties 
  which 
  can 
  be 
  

   determined 
  by 
  cutting 
  the 
  minerals 
  in 
  very 
  thin 
  slices 
  and 
  exam- 
  

   ining 
  these 
  by 
  means 
  of 
  optical 
  instruments. 
  While 
  there 
  are 
  

   over 
  700 
  recognized 
  mineral 
  species, 
  only 
  a 
  small 
  number 
  are 
  

   important 
  to 
  the 
  geologist 
  as 
  rock 
  making 
  minerals. 
  Of 
  these 
  a 
  

   few 
  are 
  sometimes 
  found 
  to 
  be 
  the 
  single 
  components 
  of 
  entire 
  

   rock 
  masses. 
  

  

  Quartz, 
  the 
  crystalline 
  form 
  of 
  silica, 
  is 
  frequently 
  found 
  In 
  

   large 
  masses 
  in 
  mineral 
  veins 
  and, 
  in 
  its 
  fragmental 
  form, 
  con- 
  

   stitutes 
  beds 
  of 
  gravel 
  and 
  sand 
  when 
  loose 
  and, 
  when 
  solidified 
  

   by 
  cementation, 
  forms 
  conglomerates, 
  sandstones 
  and 
  quartzites. 
  

  

  Calcite 
  and 
  aragonite 
  are 
  two 
  crystalline 
  forms 
  of 
  carbonate 
  

   of 
  lime, 
  the 
  former 
  of 
  which 
  is 
  the 
  chief 
  constituent 
  of 
  many 
  

   great 
  beds 
  of 
  limestone 
  ; 
  the 
  latter 
  is 
  usually 
  deposited 
  by 
  water 
  

   in 
  forms 
  called 
  stalactites, 
  calcareous 
  tufa, 
  travertine, 
  etc. 
  

  

  Dolomite, 
  the 
  double 
  carbonate 
  of 
  lime 
  and 
  magnesia 
  wholly 
  

   or 
  in 
  part 
  forms 
  extensive 
  strata 
  of 
  magnesian 
  limestone. 
  

  

  Kaolinite, 
  the 
  hydrous 
  silicate 
  of 
  alumina, 
  is 
  also 
  a 
  very 
  prom- 
  

   inent 
  mineral 
  in 
  rock 
  masses. 
  In 
  its 
  pure 
  condition 
  it 
  forms 
  

   beds 
  of 
  potter's 
  clay, 
  and 
  mingled 
  with 
  various 
  kinds 
  of 
  rock- 
  

   dust 
  it 
  constitutes 
  extensive 
  strata 
  of 
  clay 
  and 
  shale. 
  

  

  Of 
  the 
  minerals 
  which 
  mingle 
  in 
  the 
  formation 
  of 
  rocks, 
  the 
  

   most 
  important 
  are 
  quartz, 
  the 
  feldspars 
  and 
  the 
  magnesia-iron 
  

   silicates. 
  

  

  a 
  For 
  an 
  elementary 
  disenssiou 
  of 
  crystallography 
  as 
  well 
  as 
  of 
  mineralogy 
  the 
  

   reader 
  is 
  referred 
  to 
  Dana's 
  Manual 
  of 
  Lithology 
  and 
  Mineralogy. 
  

  

  