﻿Washington 
  — 
  Some 
  Lavas 
  of 
  Monte 
  Arci, 
  Sardinia. 
  589 
  

  

  brown 
  color 
  — 
  this 
  color 
  sometimes 
  extending 
  through 
  the 
  

   whole 
  crystal, 
  and 
  less 
  often 
  only 
  partially. 
  These 
  pyroxenes 
  

   look, 
  at 
  first 
  sight, 
  like 
  olivines 
  partly 
  altered 
  to 
  iddingsite. 
  

   A 
  little 
  alkali 
  feldspar 
  occurs 
  in 
  patches, 
  but 
  the 
  interstitial 
  

   material 
  is 
  mostly 
  a 
  black 
  dusty 
  substance, 
  which 
  high 
  powers 
  

   resolve 
  into 
  a 
  colorless 
  glass 
  thickly 
  crowded 
  with 
  minute, 
  

   black, 
  spherical 
  globulites. 
  As 
  the 
  usual 
  ore 
  grains 
  are 
  entirely 
  

   lacking, 
  these 
  are 
  probably 
  of 
  titaniferous 
  magnetite. 
  Only 
  a 
  

   few 
  of 
  the 
  feldspars 
  and 
  still 
  fewer 
  of 
  the 
  pyroxenes 
  are 
  of 
  

   such 
  size 
  as 
  to 
  be 
  called 
  phenocrysts. 
  

  

  Another 
  type, 
  represented 
  by 
  specimens 
  from 
  the 
  Kione 
  

   Muratta, 
  near 
  Canale 
  Perdiera, 
  and 
  from 
  Santa 
  Suina 
  chapel, 
  

   is 
  finer 
  grained 
  and 
  decidedly 
  andesitic 
  or 
  trachytic 
  in 
  texture. 
  

   The 
  feldspar 
  tables 
  are 
  much 
  smaller 
  and 
  thinner, 
  are 
  some- 
  

   what 
  more 
  sodic, 
  and 
  show 
  a 
  tendency 
  to 
  fluidal 
  parallel 
  

   arrangement. 
  The 
  colorless 
  pyroxenes 
  are 
  nearly 
  all 
  of 
  hyper- 
  

   sthene, 
  in 
  small 
  anhedra 
  or 
  subhedral 
  prisms, 
  and 
  are 
  not 
  

   colored 
  yellow 
  as 
  is 
  the 
  preceding 
  type. 
  Some 
  euhedral 
  to 
  

   subhedral 
  grains 
  of 
  olivine, 
  with 
  iddingsite 
  borders, 
  are 
  present. 
  

   Magnetite 
  grains 
  are 
  rather 
  common 
  in 
  this 
  type. 
  There 
  is 
  

   very 
  little 
  colorless 
  interstitial 
  glass. 
  Except 
  for 
  the 
  presence 
  

   of 
  olivine 
  these 
  basalts 
  greatly 
  resemble 
  the 
  andesites 
  just 
  de- 
  

   scribed, 
  and 
  are 
  best 
  to 
  be 
  regarded 
  as 
  andesite-basalts. 
  

  

  Only 
  one 
  analysis 
  was 
  made 
  of 
  these 
  rocks, 
  there 
  being 
  given 
  

   for 
  comparison 
  an 
  analysis 
  of 
  a 
  basalt 
  from 
  Monte 
  Ferru 
  and 
  

   one 
  from 
  Ploaghe. 
  

  

  Analyses 
  of 
  Sardinian 
  Basalts. 
  

  

  B 
  

  

  Aa 
  

  

  

  Si0 
  2 
  

  

  52-79 
  

  

  52-40 
  

  

  56-34 
  

  

  52-67 
  

  

  ■880 
  

  

  

  A1 
  2 
  8 
  

  

  1645 
  

  

  15-26 
  

  

  13-95 
  

  

  1535 
  

  

  •161 
  

  

  

  Fe 
  2 
  3 
  

  

  2-74 
  

  

  0-74 
  

  

  1-94 
  

  

  3-82 
  

  

  •017 
  

  

  

  FeO 
  

  

  6-44 
  

  

  8-33 
  

  

  6-73 
  

  

  5-42 
  

  

  •089 
  

  

  

  MgO 
  

  

  5-56 
  

  

  7-45 
  

  

  6-41 
  

  

  4-40 
  

  

  •139 
  

  

  

  CaO 
  

  

  6-51 
  

  

  7-33 
  

  

  6-20 
  

  

  5-91 
  

  

  •116 
  

  

  

  Na 
  2 
  

  

  3-64 
  

  

  3-54 
  

  

  3-10 
  

  

  4-50 
  

  

  •059 
  

  

  

  K 
  2 
  

  

  1-21 
  

  

  0-99 
  

  

  0-76 
  

  

  2-68 
  

  

  •013 
  

  

  

  H 
  2 
  + 
  

  

  1-02 
  

  

  0-29 
  

  

  1-04 
  

  

  0-37 
  

  

  

  

  H 
  2 
  0- 
  

  

  0-21 
  

  

  0-06 
  

  

  0-63 
  

  

  0-14 
  

  

  

  

  TiO 
  a 
  

  

  2-64 
  

  

  3-12 
  

  

  2*22 
  

  

  4-04 
  

  

  •033 
  

  

  

  P 
  2 
  5 
  

  

  0-39 
  

  

  0-49 
  

  

  0-44 
  

  

  0-75 
  

  

  •003 
  

  

  

  MnO 
  

  

  0-06 
  

  

  0-08 
  

  

  

  trace 
  

  

  

  

  NiO 
  

  

  0-18 
  

  

  99-84 
  

  

  0-06 
  

  

  99-76 
  

  

  none 
  

  

  •002 
  

  

  

  100-14 
  

  

  100-05 
  

  

  

  A. 
  

  

  Uras, 
  Monte 
  Arci. 
  

  

  

  

  

  

  B. 
  

  

  Near 
  Cuglieri, 
  Monte 
  Ferru. 
  

  

  

  

  

  C. 
  

  

  Andesite 
  

  

  , 
  Canale 
  Perdiera, 
  Monte 
  Arci. 
  

  

  

  

  D. 
  

  

  Basalt. 
  

  

  Monte 
  San 
  Mateo, 
  Ploaghe 
  

  

  

  

  

  Aa 
  

  

  Mol 
  numbers 
  of 
  A. 
  

  

  

  

  

  

  