﻿10 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  The 
  rock 
  is 
  medium-grained, 
  dark 
  gray, 
  and 
  very 
  coarsely 
  vesic- 
  

   ular. 
  The 
  modal 
  composition 
  is 
  as 
  follows 
  : 
  

  

  Mineral 
  composition 
  of 
  basalt 
  from 
  La 
  Jura 
  Creek 
  Colo. 
  

  

  Plagioclase 
  (oligoclase) 
  60. 
  

  

  Augite 
  28. 
  6 
  

  

  Olivine 
  1. 
  3 
  

  

  Iddingsite 
  3. 
  8 
  

  

  Magnetite 
  0. 
  6 
  

  

  Total 
  100. 
  

  

  The 
  iddingsite 
  occurs 
  in 
  masses 
  of 
  a 
  maximum 
  diameter 
  of 
  4 
  

   millimeters, 
  whose 
  outlines 
  are 
  those 
  of 
  olivine. 
  The 
  olivine 
  is 
  only 
  

   partly 
  altered 
  to 
  iddingsite, 
  but 
  the 
  greater 
  specific 
  gravity 
  of 
  olivine 
  

   allows 
  an 
  almost 
  complete 
  separation 
  of 
  the 
  two 
  minerals. 
  Part 
  of 
  

   the 
  alteration 
  product 
  of 
  olivine 
  was 
  a 
  lemon 
  yellow 
  material, 
  which 
  

   under 
  the 
  microscope 
  appeared 
  to 
  be 
  cryptocrystalline. 
  This 
  ma- 
  

   terial 
  has 
  a 
  lower 
  specific 
  gravity 
  than 
  crystalline 
  iddingsite 
  and 
  is 
  

   represented 
  by 
  analysis 
  No. 
  3. 
  It 
  contains 
  many 
  minute, 
  highly 
  

   magnetic 
  black 
  inclusions 
  arranged 
  in 
  lines 
  running 
  parallel 
  to 
  the 
  

   crystallographic 
  axes, 
  which 
  are 
  undoubtedly 
  magnetite. 
  

  

  BERNARDS 
  FERRY, 
  IDAHO, 
  OCCURRENCE 
  

  

  A 
  specimen 
  of 
  basalt 
  from 
  Bernards 
  Ferry, 
  Silver 
  City 
  quad- 
  

   rangle, 
  Owyhee 
  County, 
  Idaho, 
  contained 
  in 
  Lindgren's 
  12 
  studied 
  

   series 
  of 
  rocks 
  yielded 
  the 
  iddingsite 
  used 
  in 
  analysis 
  No. 
  4. 
  The 
  

   rock 
  contains 
  abundant 
  reddish 
  brown 
  iddingsite, 
  although 
  Lindgren 
  

   does 
  not 
  mention 
  olivine 
  or 
  iddingsite 
  in 
  his 
  brief 
  description 
  of 
  the 
  

   basalts 
  of 
  the 
  region. 
  The 
  rock 
  is 
  coarse-grained, 
  slightly 
  vesicular, 
  

   and 
  dark 
  gray. 
  The 
  modal 
  composition 
  is 
  as 
  follows 
  : 
  

  

  Mineral 
  composition 
  of 
  the 
  basalt 
  from 
  Bernards 
  Ferry, 
  Idaho 
  

  

  Plagioclase 
  AbssAnsa 
  46. 
  

  

  Augite 
  43. 
  3 
  

  

  Olivine 
  2. 
  6 
  

  

  Iddingsite 
  5. 
  9 
  - 
  

  

  Magnetite 
  2. 
  2 
  

  

  Total 
  100. 
  

  

  The 
  iddingsite 
  is 
  dark 
  reddish 
  brown 
  and 
  occurs 
  as 
  pseudomorphs 
  

   after 
  olivine. 
  The 
  larger 
  grains 
  are 
  completely 
  altered 
  to 
  iddingsite, 
  

   but 
  some 
  of 
  the 
  smaller 
  ones 
  show 
  outer 
  borders 
  of 
  olivine 
  around 
  

   cores 
  of 
  iddingsite. 
  

  

  As 
  in 
  the 
  occurrence 
  previously 
  described, 
  the 
  Bernards 
  Ferry 
  

   rock 
  contains 
  a 
  cryptociystalline 
  substance 
  derived 
  from 
  the 
  olivine 
  

   in 
  the 
  same 
  manner 
  as 
  the 
  deeper 
  red 
  crystalline 
  material 
  which 
  is 
  

  

  12 
  Lindgren, 
  Waldemar, 
  U. 
  S. 
  Geol. 
  Surv. 
  Ann. 
  Rept. 
  20, 
  pt. 
  3. 
  

  

  