﻿ACTION 
  OF 
  WATER 
  ON 
  MINERALS 
  OF 
  THE 
  MICA 
  FAMILY. 
  363 
  

  

  22. 
  On 
  the 
  Action 
  of 
  Pure 
  Water, 
  and 
  of 
  Water 
  saturated 
  with 
  

   Carbonic 
  Acid 
  Gas, 
  on 
  the 
  Minerals 
  of 
  the 
  Mica 
  Familt. 
  By 
  

   Alexander 
  Johnstone, 
  F.G.S., 
  Assistant 
  to 
  the 
  Professor 
  

   of 
  Geology 
  and 
  Mineralogy 
  in 
  the 
  University 
  of 
  Edinburgh, 
  

   (Eead 
  February 
  20, 
  1889.) 
  

  

  In 
  papers 
  which 
  have 
  been 
  published 
  in 
  the 
  ' 
  Transactions 
  ' 
  of 
  the 
  

   Royal 
  and 
  Geological 
  Societies 
  of 
  Edinburgh 
  *, 
  the 
  Author 
  has 
  

   already 
  given 
  preliminary 
  accounts 
  of 
  certain 
  of 
  his 
  researches 
  

   into 
  the 
  nature 
  of 
  the 
  action 
  of 
  water 
  saturated 
  with 
  carbonic 
  acid 
  

   gas 
  on 
  the 
  following 
  mineral 
  and 
  rock 
  substances 
  : 
  — 
  Orthoclase, 
  

   oligoclase, 
  labradorite, 
  muscovite 
  and 
  biotite, 
  hornblende, 
  augite, 
  

   olivine, 
  steatite, 
  magnetite, 
  haematite, 
  calcite, 
  siderite, 
  and 
  statuary 
  

   marble 
  (cr3 
  T 
  stalline 
  limestone). 
  

  

  In 
  the 
  present 
  communication 
  he 
  wishes 
  to 
  give 
  some 
  details 
  of 
  

   observations 
  noted, 
  and 
  results 
  of 
  experiments 
  carried 
  out, 
  while 
  

   engaged 
  in 
  recent 
  investigations 
  into 
  the 
  nature 
  of 
  the 
  changes 
  

   produced 
  by 
  pure 
  distilled 
  water, 
  and 
  also 
  by 
  water 
  saturated 
  with 
  

   carbonic 
  acid, 
  on 
  the 
  principal 
  members 
  of 
  the 
  mica 
  family 
  of 
  

   minerals. 
  

  

  Classification 
  of 
  the 
  Micas. 
  

  

  It 
  is 
  convenient 
  for 
  all 
  ordinary 
  purposes 
  to 
  arrange 
  the 
  micas 
  

   into 
  two 
  great 
  classes. 
  Division 
  I. 
  comprehends 
  the 
  varieties 
  which 
  

   are 
  anhydrous 
  or 
  practically 
  so 
  : 
  Division 
  II. 
  includes 
  the 
  micas 
  

   which 
  are 
  most 
  distinctly 
  hydrated. 
  

  

  Division 
  I. 
  

  

  In 
  this 
  section 
  the 
  micas 
  generally 
  known 
  as 
  muscovite 
  (inclu- 
  

   ding 
  lepidolite 
  &c.) 
  and 
  biotite 
  (including 
  phlogopite 
  and 
  lepido- 
  

   melane 
  &c.) 
  are 
  placed. 
  They 
  are 
  specially 
  characterized 
  by 
  the 
  

   possession 
  of 
  a 
  splendent 
  or 
  shining 
  lustre, 
  and 
  of 
  a 
  high 
  degree 
  of 
  

   elasticity 
  in 
  their 
  fine 
  lamina?. 
  Normal 
  specimens 
  of 
  these 
  varieties 
  

   contain 
  usually 
  from 
  about 
  1 
  to 
  1*9 
  per 
  cent, 
  of 
  water, 
  and 
  none 
  

   belonging 
  properly 
  to 
  this 
  division 
  have 
  more 
  than 
  2'5 
  per 
  cent, 
  of 
  

   that 
  liquid 
  in 
  their 
  composition. 
  They 
  pass, 
  however, 
  quite 
  gradu- 
  

   ally, 
  by 
  the 
  increase 
  of 
  water 
  from 
  2-5 
  to 
  5 
  or 
  6 
  per 
  cent., 
  over 
  into 
  

   the 
  next 
  division, 
  known 
  as 
  the 
  hydromicas. 
  

  

  * 
  " 
  On 
  the 
  Action 
  of 
  Carbonic 
  Acid 
  Water 
  on 
  Minerals 
  and 
  Bocks," 
  Trans- 
  

   actions 
  Edinburgh 
  Greological 
  Society, 
  vol. 
  v. 
  p. 
  282. 
  " 
  On 
  the 
  Action 
  of 
  

   Carbonic 
  Acid 
  Water 
  on 
  Olivine," 
  Proceedings 
  Royal 
  Society 
  of 
  Edinburgh, 
  

   No. 
  127. 
  " 
  The 
  Prolonged 
  Action 
  of 
  Sea 
  Water 
  on 
  Pure 
  Natural 
  Magnesium 
  

   Silicates," 
  Proceedings 
  Royal 
  Society 
  of 
  Edinburgh, 
  No. 
  128. 
  

  

  