﻿44 
  Washington 
  — 
  Analyses 
  of 
  Italian 
  Volcanic 
  Rocks. 
  

  

  Art. 
  YL 
  — 
  Some 
  Analyses 
  of 
  Italian 
  Volcanic 
  Hocks, 
  II 
  ; 
  

   by 
  Henry 
  S. 
  Washington. 
  

  

  [Continued 
  from 
  p. 
  294, 
  vol. 
  viii.] 
  

  

  Ciminite, 
  Monte 
  Cimino, 
  Viterho. 
  — 
  In 
  1896* 
  I 
  described 
  

   certain 
  trachytic 
  rocks 
  from 
  this 
  region, 
  giving 
  them 
  the 
  name 
  

   of 
  ciminite, 
  derived 
  from 
  this 
  locality, 
  where 
  they 
  are 
  found 
  

   in 
  typical 
  development. 
  They 
  are 
  composed 
  essentially 
  of 
  

   alkali 
  and 
  lime-soda 
  feldspars, 
  augite 
  and 
  olivine, 
  the 
  presence 
  

   of 
  the 
  last 
  mineral 
  and 
  their 
  more 
  basic 
  character 
  distinguish- 
  

   ing 
  -them 
  from 
  the 
  closely 
  related 
  vulsinites. 
  Both 
  from 
  a 
  

   chemical 
  and 
  mineralogical 
  point 
  of 
  view 
  they 
  stand 
  inter- 
  

   mediate 
  between 
  the 
  trachytes 
  and 
  the 
  andesites 
  and 
  basalts, 
  

   and 
  are 
  hence 
  monzonitic 
  in 
  character. 
  They 
  belong 
  to 
  the 
  

   group 
  which 
  Rosenbusch 
  has 
  called 
  andesitic 
  trachytes 
  and 
  

   trachydoleritesf 
  and 
  for 
  which 
  RansomeJ 
  has 
  proposed 
  the 
  

   name 
  of 
  latite. 
  

  

  As 
  another 
  analysis 
  seemed 
  desirable 
  to 
  establish 
  the 
  type 
  

   more 
  definitely, 
  one 
  was 
  made 
  of 
  a 
  specimen 
  from 
  a 
  flow 
  at 
  

   La 
  Colonetta, 
  on 
  the 
  south 
  slope 
  of 
  Monte 
  Cimino. 
  It 
  is 
  

   rather 
  dark 
  gray, 
  dense 
  and 
  compact, 
  with 
  some 
  vesicles. 
  A 
  

   few 
  phenocrysts 
  of 
  glassy 
  feldspar 
  (orthoclase 
  and 
  labradorite), 
  

   augite 
  and 
  olivine 
  are 
  visible. 
  In 
  thin 
  section 
  it 
  resembles 
  

   those 
  already 
  described, 
  though 
  olivine 
  phenocrysts 
  are 
  some- 
  

   what 
  more 
  abundant, 
  and 
  the 
  groundmass 
  is 
  denser, 
  with 
  a 
  

   felt 
  of 
  minute 
  orthoclase 
  and 
  some 
  labradorite 
  laths 
  lying 
  in 
  a 
  

   glassy 
  base. 
  

  

  I 
  II 
  ill 
  

  

  SiO„ 
  .57-31 
  55-44 
  55*46 
  

  

  Ti0 
  2 
  0-40 
  0-16 
  0-16 
  

  

  A1 
  2 
  3 
  14-71 
  18-60 
  15-36 
  

  

  Fe 
  2 
  3 
  1-21 
  2-09 
  1-34 
  

  

  FeO 
  4-37 
  4-48 
  4-50 
  

  

  MnO 
  trace 
  trace 
  trace 
  

  

  M^O 
  7-80 
  4-75 
  7-90 
  

  

  CaO. 
  ._.... 
  6-90 
  6-76 
  6'69 
  

  

  BaO 
  none 
  

  

  Na 
  2 
  1-35 
  1-79 
  1-79 
  

  

  K 
  2 
  U 
  638 
  6-63 
  663 
  

  

  H 
  2 
  O(ll0°-)) 
  0-15 
  

  

  H 
  2 
  O(110° 
  + 
  ) 
  \ 
  "-- 
  ° 
  18 
  ° 
  25 
  0-23 
  

  

  P 
  2 
  3 
  trace 
  trace 
  

  

  100-61 
  100-95 
  10021 
  

  

  * 
  Jour. 
  Geol., 
  iv, 
  p. 
  834, 
  1896; 
  also 
  v, 
  p. 
  351, 
  1897. 
  

  

  \ 
  Rosenbusch, 
  Elemente 
  der 
  Gesteinslehre, 
  p. 
  339, 
  1898. 
  

  

  \ 
  Ransome, 
  this 
  Journal, 
  vol. 
  v, 
  355 
  and 
  364 
  £f, 
  1898. 
  

  

  