﻿' 
  THE 
  MINING 
  AND 
  QUARRY 
  INDUSTRY 
  I908 
  85 
  

  

  dip 
  as 
  the 
  latter 
  and 
  are 
  at 
  times 
  continuous 
  for 
  long 
  distances, 
  as 
  

   at 
  Talcviile 
  where 
  workable 
  deposits 
  extend 
  fully 
  a 
  mile 
  along 
  the 
  

   outcrop. 
  

  

  The 
  derivation 
  of 
  the 
  talc 
  has 
  been 
  explained 
  by 
  C. 
  H. 
  Smyth 
  jr 
  

   as 
  due 
  to 
  chemical 
  alteration 
  of 
  silicates 
  produced 
  during 
  the 
  

   metamorphism 
  of 
  the 
  limestone. 
  Originally 
  an 
  impure 
  calcareous 
  

   sediment, 
  the 
  limestone 
  under 
  dynamic 
  influences, 
  has 
  taken 
  on 
  a 
  

   crystalline 
  character 
  and 
  became 
  impregnated 
  with 
  silicates, 
  chiefly 
  

   tremolite, 
  actinolite 
  and 
  pyroxene. 
  Certain 
  beds 
  seem 
  to 
  have 
  con- 
  

   tained 
  sufficient 
  magnesia 
  and 
  silica 
  to 
  permit 
  a 
  complete 
  trans- 
  

   formation 
  into 
  tremolite, 
  forming 
  a 
  tremolite 
  schist, 
  while 
  other 
  

   layers 
  with 
  a 
  preponderance 
  of 
  lime 
  have 
  undergone 
  a 
  partial 
  

   change, 
  showing 
  scattered 
  crystals 
  and 
  aggregates 
  of 
  silicates 
  within 
  

   the 
  crystalline 
  limestone. 
  Tremolite 
  is 
  always 
  the 
  principal 
  silicate 
  

   in 
  vicinity 
  of 
  the 
  talc 
  beds, 
  though 
  elsewhere 
  pyroxene 
  (enstatite 
  

   and 
  diopside) 
  is 
  common. 
  The 
  change 
  from 
  tremolite 
  to 
  talc 
  is 
  

   a 
  result 
  of 
  weathering, 
  and 
  takes 
  place 
  readily 
  under 
  the 
  influence 
  

   of 
  ground 
  waters 
  holding 
  carbon 
  dioxid. 
  A 
  coordinate 
  process 
  has 
  

   produced 
  serpentine 
  from 
  the 
  same 
  silicates, 
  though 
  this 
  mineral 
  

   is 
  seldom 
  found 
  with 
  the 
  talc, 
  being 
  confined 
  so 
  far 
  as 
  observed 
  

   to 
  the 
  outlying 
  areas. 
  The 
  principle 
  determining 
  the 
  nature 
  of 
  the 
  

   end 
  product, 
  whether 
  talc 
  or 
  serpentine, 
  seems 
  to 
  be 
  a 
  problem 
  not 
  

   yet 
  solved. 
  The 
  alteration 
  of 
  tremolite 
  to 
  talc, 
  according 
  to 
  Van 
  

   Hise,^ 
  may 
  be 
  given 
  the 
  following 
  chemical 
  formula: 
  

  

  Ca 
  Mg, 
  Si, 
  O,, 
  + 
  H,0 
  + 
  CO, 
  = 
  H, 
  Mg, 
  Si, 
  O^, 
  + 
  CaCO., 
  

  

  The 
  alteration 
  is 
  accompanied 
  by 
  an 
  increase 
  in 
  volume 
  of 
  talc 
  

   and 
  calcite 
  amounting 
  to 
  25.61 
  per 
  cent, 
  though 
  if 
  the 
  talc 
  alone 
  is 
  

   considered 
  there 
  is 
  a 
  decrease 
  of 
  .83 
  per 
  cent 
  as 
  compared 
  with 
  the 
  

   tremolite. 
  There 
  is 
  little 
  or 
  no 
  calcite 
  present 
  in 
  the 
  talc 
  ; 
  it 
  has 
  

   doubtless 
  been 
  removed 
  by 
  the 
  water 
  circulations 
  during 
  the 
  process 
  

   of 
  alteration. 
  

  

  The 
  beds 
  under 
  exploitation 
  range 
  from 
  a 
  few 
  feet 
  up 
  to 
  50 
  feet 
  

   or 
  more 
  in 
  thickness. 
  They 
  are 
  inclined 
  at 
  varying 
  angles, 
  usually 
  

   between 
  30° 
  and 
  60°, 
  from 
  the 
  horizontal. 
  The 
  dip 
  is 
  uniformly 
  

   toward 
  the 
  northwest. 
  Masses 
  and 
  seams 
  of 
  unaltered 
  tremolite 
  

   are 
  sometimes 
  included 
  within 
  the 
  deposits. 
  

  

  Character 
  of 
  the 
  talc. 
  The 
  characteristic 
  product 
  of 
  the 
  region 
  

   has 
  a 
  fibrous 
  texture, 
  belonging 
  to 
  the 
  variety 
  known 
  as 
  agalitc. 
  

   It 
  is 
  in 
  fact 
  a 
  pseudomorph 
  of 
  tremolite, 
  to 
  which 
  the 
  fibrous 
  

  

  1 
  Treatise 
  on 
  Metamorphism, 
  p. 
  286. 
  

  

  