﻿868 
  ACTION 
  OF 
  WATER 
  ON 
  MINERALS 
  OF 
  THE 
  MICA 
  FAMILY. 
  

  

  Iii 
  the 
  water 
  of 
  the 
  other 
  vessel, 
  however, 
  which 
  was 
  saturated 
  

   with 
  carbonic 
  acid 
  gas, 
  distinct 
  traces 
  of 
  the 
  bases 
  magnesia 
  and 
  

   iron 
  were 
  found 
  in 
  a 
  state 
  of 
  solution, 
  so 
  that 
  when 
  the 
  liquid 
  

   was 
  evaporated 
  down 
  the 
  substances 
  remained 
  behind, 
  as 
  whitish 
  

   carbonates 
  *, 
  to 
  form 
  a 
  very 
  small, 
  but 
  quite 
  distinct, 
  residue. 
  The 
  

   biotite 
  which 
  had 
  been 
  exposed 
  to 
  the 
  action 
  of 
  the 
  carbonated 
  

   water 
  had 
  then, 
  evidently, 
  besides 
  undergoing 
  hydration, 
  been 
  chemi- 
  

   cally 
  decomposed 
  to 
  a 
  slight 
  extent. 
  

  

  Here 
  follow 
  three 
  analyses; 
  the 
  first 
  (V.) 
  of 
  the 
  original 
  fresh 
  

   biotite, 
  the 
  second 
  (VI.) 
  of 
  the 
  specimen 
  of 
  biotite 
  which 
  had 
  been 
  

   subjected 
  to 
  the 
  action 
  of 
  the 
  pure 
  water, 
  and 
  the 
  third 
  (VII.) 
  of 
  

   the 
  biotite 
  which 
  had 
  been 
  suspended 
  in 
  the 
  carbonic-acid 
  water 
  : 
  — 
  

  

  V. 
  VI. 
  VII. 
  

  

  Silica 
  41-02 
  40-79 
  42-10 
  

  

  Alumina.. 
  17*99 
  16-81 
  19-45 
  

  

  Magnesia 
  20-04 
  18-90 
  17'35 
  

  

  Potash 
  9-35 
  7*99 
  8-14 
  

  

  Eerric 
  Oxide 
  10%50 
  9-85 
  8-20 
  

  

  Soda 
  

  

  ! 
  

  

  r 
  traces. 
  traces. 
  traces. 
  

  

  Manganese 
  

  

  Water 
  ' 
  1'71 
  5-52 
  5-83 
  

  

  100-61 
  99-86 
  101-07 
  

  

  The 
  third 
  analysis 
  (VII.) 
  shows 
  a 
  decided 
  loss 
  of 
  magnesia 
  and 
  

   iron. 
  It 
  seems 
  to 
  the 
  Author 
  that 
  if 
  his 
  experiments 
  had 
  run 
  on 
  

   for 
  a 
  score 
  of 
  years 
  instead 
  of 
  one, 
  even 
  the 
  suspended 
  mass 
  of 
  

   biotite 
  in 
  the 
  carbonated 
  water 
  would, 
  at 
  the 
  end 
  of 
  that 
  period, 
  

   by 
  the 
  continued 
  loss 
  of 
  magnesia 
  and 
  iron, 
  have 
  shown 
  a 
  decided 
  

   resemblance, 
  both 
  chemically 
  and 
  physically, 
  to 
  any 
  ordinary 
  hydro- 
  

   muscovite. 
  Possibly 
  many 
  of 
  the 
  hydromuscovite 
  scales 
  found 
  in 
  

   hornblende-schists, 
  gneisses, 
  and 
  granites 
  may 
  originally 
  have 
  been 
  

   biotites 
  which 
  have 
  undergone 
  alteration 
  in 
  the 
  manner 
  described. 
  

  

  The 
  Author 
  has 
  also 
  subjected 
  lepidomelane 
  to 
  the 
  action 
  of 
  pure 
  

   and 
  of 
  carbonated 
  water. 
  In 
  the 
  former 
  case 
  hydration 
  only 
  re- 
  

   sulted 
  ; 
  but 
  in 
  the 
  latter 
  liquid, 
  in 
  addition 
  to 
  hydration, 
  loss 
  of 
  

   iron 
  was 
  brought 
  about 
  by 
  the 
  action 
  of 
  the 
  carbonic 
  acid. 
  

  

  When 
  any 
  ordinary 
  hydrobiotite, 
  such 
  as 
  voigtite, 
  vermiculite, 
  or 
  

   pyrosclerite, 
  was 
  exposed 
  for 
  a 
  lengthened 
  period 
  to 
  the 
  action 
  of 
  

   carbonic-acid 
  water, 
  it 
  was 
  noted 
  that 
  the 
  mineral 
  invariably 
  

   lost 
  a 
  portion 
  of 
  its 
  magnesia 
  and 
  iron, 
  which 
  were 
  first, 
  by 
  the 
  

   action 
  of 
  the 
  carbonic 
  acid 
  gas, 
  converted 
  into 
  carbonates, 
  and 
  then, 
  

   as 
  such, 
  removed 
  in 
  solution. 
  

  

  In 
  concluding, 
  it 
  appears 
  to 
  the 
  Author 
  that 
  a 
  fact, 
  which 
  he 
  has 
  

   by 
  careful 
  observation 
  ascertained, 
  should 
  be 
  recorded 
  here, 
  viz. 
  

   that 
  whenever 
  anhydrous 
  micas, 
  or 
  lower-hydrated 
  micas, 
  become 
  

   hydrated, 
  or 
  more 
  highly 
  hydrated, 
  they 
  always 
  at 
  the 
  same 
  time 
  

   increase 
  in 
  bulk. 
  This 
  fact 
  may 
  help 
  to 
  explain 
  what 
  has 
  never 
  

   been 
  well 
  understood, 
  the 
  nature 
  and 
  an 
  important 
  cause 
  of 
  the 
  

   rapid 
  weathering 
  of 
  micaceous 
  sandstones. 
  

  

  * 
  After 
  exposure 
  to 
  the 
  air 
  for 
  a 
  day 
  or 
  so, 
  this 
  residue 
  darkened 
  and 
  

   browned 
  somewhat, 
  owing, 
  of 
  course, 
  to 
  the 
  oxidation 
  of 
  the 
  iron 
  present. 
  

  

  