﻿THE 
  ORIGIN, 
  OCCURRENCE, 
  COMPOSITION, 
  AND 
  PHYSI- 
  

   CAL 
  PROPERTIES 
  OF 
  THE 
  MINERAL 
  IDDINGSITE 
  

  

  Ity 
  Clarence 
  S. 
  Ross 
  

   Geologist, 
  United 
  States 
  Geological 
  Survey 
  

  

  and 
  

  

  Earl 
  V. 
  Shannon 
  

   Assistant 
  Curator 
  of 
  Geology, 
  United 
  States 
  National 
  Museum 
  

  

  INTRODUCTION 
  

  

  Dr. 
  A. 
  C. 
  Lawson, 
  1 
  while 
  studying 
  the 
  volcanic 
  rocks 
  in 
  the 
  vicinity 
  

   of 
  Carmelo 
  Bay, 
  Calif., 
  in 
  1893, 
  found 
  an 
  undescribed 
  mineral 
  in 
  the 
  

   rocks 
  called 
  carmeloites, 
  to 
  which 
  he 
  gave 
  the 
  name 
  iddingsite 
  ; 
  that, 
  

   however, 
  the 
  mineral 
  was 
  a 
  distinct 
  species 
  was 
  not 
  generally 
  recog- 
  

   nized 
  and 
  it 
  is 
  still 
  described 
  in 
  the 
  textbooks 
  as 
  a 
  variety 
  of 
  serpen- 
  

   tine. 
  2 
  Subsequent 
  study 
  has 
  shown 
  this 
  to 
  be 
  a 
  widespread 
  and, 
  

   at 
  times, 
  an 
  abundant 
  mineral 
  in 
  basaltic 
  rocks, 
  but 
  its 
  chemical 
  com- 
  

   position 
  and 
  real 
  nature 
  have 
  long 
  remained 
  matters 
  of 
  speculation. 
  

   It 
  is 
  a 
  secondary 
  mineral, 
  rarely 
  entirely 
  free 
  from 
  the 
  olivine 
  from 
  

   which 
  it 
  is 
  derived; 
  it 
  is 
  rather 
  finely 
  disseminated 
  among 
  other 
  

   minerals 
  of 
  nearly 
  the 
  same 
  specific 
  gravity, 
  and 
  so 
  investigators 
  

   have 
  been 
  deterred 
  from 
  making 
  the 
  tedious 
  efforts 
  required 
  for 
  its 
  

   separation 
  and 
  analysis. 
  

  

  The 
  chemical 
  portion 
  of 
  the 
  following 
  paper 
  is 
  based 
  upon 
  eight 
  

   analyses 
  of 
  iddingsite 
  from 
  six 
  localities, 
  and 
  while 
  the 
  results 
  of 
  

   these 
  analyses 
  do 
  not 
  give 
  a 
  complete 
  understanding 
  of 
  the 
  chemical 
  

   composition 
  of 
  iddingsite, 
  they 
  show 
  that 
  it 
  is 
  not 
  serpentine 
  and 
  

   establish 
  it 
  as 
  a 
  distinct 
  mineral 
  species. 
  All 
  the 
  analyzed 
  iddingsites, 
  

   and 
  additional 
  materials 
  from 
  widely 
  separated 
  localities 
  from 
  the 
  

   western 
  United 
  States, 
  have 
  been 
  examined; 
  the 
  physical 
  properties 
  

   have 
  been 
  determined; 
  its 
  relations 
  to 
  the 
  associated 
  minerals 
  have 
  

  

  1 
  Lawson, 
  Andrew 
  C, 
  Univ. 
  of 
  Calif. 
  Bull, 
  of 
  Dept. 
  of 
  Geol., 
  No. 
  1, 
  p. 
  31. 
  1893. 
  

  

  2 
  Johannsen, 
  Albert, 
  Determination 
  of 
  rock-forming' 
  minerals, 
  p. 
  361, 
  New 
  York, 
  1908. 
  

   Iddings, 
  Joseph 
  P., 
  Rock 
  minerals, 
  p. 
  381, 
  New 
  York, 
  1911. 
  Winchell, 
  N. 
  H., 
  and 
  A. 
  N., 
  

   Elements 
  of 
  optical 
  mineralogy, 
  p. 
  300, 
  New 
  York, 
  1909. 
  

  

  No. 
  2579— 
  Proceedings 
  U. 
  S. 
  National 
  Museum, 
  Vol. 
  67, 
  Art. 
  7. 
  

  

  23555—25 
  1 
  1 
  

  

  