﻿304 
  C. 
  W. 
  JENKS 
  ON 
  THE 
  OCCURRENCE 
  OF 
  

  

  The 
  corundum 
  is 
  invariably 
  crystallized, 
  some 
  of 
  the 
  crystals 
  

   weighing 
  more 
  than 
  300 
  pounds 
  ; 
  usually 
  the 
  large 
  crystals 
  are 
  

   found 
  to 
  enclose 
  plates 
  of 
  chlorite 
  or 
  jefferisite, 
  just 
  as 
  if 
  these 
  

   minerals 
  had 
  been 
  entangled 
  in 
  the 
  very 
  act 
  of 
  the 
  crystallization 
  of 
  

   the 
  corundum 
  itself. 
  

  

  About 
  200 
  tons 
  of 
  corundum 
  have 
  already 
  been 
  extracted 
  from 
  

   this 
  mine, 
  and, 
  after 
  crushing, 
  used 
  for 
  grinding 
  and 
  polishing 
  

   stones, 
  glass, 
  and 
  metals 
  &c, 
  being 
  found 
  far 
  superior 
  to 
  emery 
  for 
  

   these 
  purposes. 
  Taking 
  the 
  sapphire 
  as 
  a 
  standard 
  at 
  100, 
  the 
  

   corundum 
  from 
  this 
  mine 
  was 
  found 
  to 
  have 
  an 
  abrasive 
  power 
  of 
  

   no 
  less 
  than 
  between 
  90 
  and 
  97, 
  whilst 
  the 
  best 
  Naxos 
  emery 
  only 
  

   stood 
  at 
  between 
  40 
  and 
  57. 
  

  

  The 
  colour 
  of 
  the 
  corundum 
  crystals 
  is 
  very 
  variable. 
  Some 
  are 
  

   perfectly 
  colourless 
  and 
  transparent, 
  while 
  others 
  have 
  all 
  shades 
  of 
  

   yellow, 
  green, 
  blue 
  (sapphire), 
  pink 
  and 
  red 
  (ruby), 
  many 
  of 
  the 
  

   crystals 
  showing 
  different 
  colours 
  in 
  different 
  parts 
  of 
  their 
  sub- 
  

   stance 
  — 
  some 
  of 
  the 
  large 
  ones, 
  when 
  fractured, 
  revealing 
  portions 
  

   coloured 
  as 
  rubies 
  or 
  sapphires, 
  from 
  which 
  many 
  gems 
  have 
  already 
  

   been 
  broken 
  out 
  and 
  cut 
  for 
  setting 
  : 
  most 
  of 
  these 
  have 
  as 
  yet, 
  

   however, 
  been 
  of 
  small 
  size, 
  owing 
  to 
  the 
  difficulty 
  of 
  finding 
  large 
  

   pieces 
  free 
  from 
  flaws 
  or 
  cleavage-planes 
  passing 
  through 
  them. 
  

   There 
  can 
  be 
  no 
  doubt 
  as 
  to 
  these 
  stones 
  being 
  the 
  true 
  gems 
  ; 
  and 
  

   Mr. 
  H. 
  C. 
  Sorby, 
  to 
  whom 
  the 
  specimens 
  have 
  been 
  submitted, 
  

   declares, 
  from 
  their 
  microscopic 
  structure, 
  that 
  they 
  must 
  have 
  been 
  

   formed 
  at 
  an 
  elevated 
  temperature, 
  and 
  that 
  they 
  contain 
  the 
  same 
  

   well-marked 
  fluid-cavities 
  filled 
  with 
  a 
  highly 
  expansive 
  liquid 
  

   (without 
  doubt 
  liquefied 
  carbonic 
  acid) 
  as 
  are 
  seen 
  in 
  the 
  sapphires 
  

   from 
  Ceylon 
  ; 
  he 
  also 
  attributes 
  the 
  colour 
  of 
  the 
  rubies 
  and 
  of 
  the 
  

   green 
  sapphire 
  to 
  chromium, 
  but 
  is 
  uncertain 
  as 
  to 
  the 
  cause 
  of 
  

   the 
  blue 
  of 
  the 
  sapphire, 
  suggesting 
  that 
  it 
  may 
  be 
  due 
  to 
  protoxide 
  

   of 
  iron 
  or 
  possibly 
  to 
  uranium 
  ; 
  and 
  he 
  sees 
  no 
  reason 
  for 
  doubting 
  

   these 
  gems 
  being 
  quite 
  identical 
  with 
  those 
  so 
  long 
  known 
  from 
  

   the 
  East. 
  

  

  The 
  serpentine 
  rock 
  of 
  the 
  Corundum 
  Hill 
  has 
  been 
  analyzed 
  by 
  

   M. 
  Th. 
  M. 
  Chatard 
  with 
  the 
  following 
  results 
  : 
  — 
  

  

  Silica 
  41-58 
  

  

  Alumina 
  0'14 
  

  

  Protoxide 
  of 
  iron 
  7 
  - 
  49 
  

  

  Protoxide 
  of 
  nickel 
  (trace 
  of 
  cobalt 
  and 
  manganese) 
  034 
  

  

  Magnesia 
  49-28 
  

  

  Lime 
  .' 
  0-11 
  

  

  Loss 
  on 
  ignition 
  1-72 
  

  

  100 
  66 
  

  

  As 
  several 
  of 
  the 
  minerals 
  occurring 
  in 
  the 
  Culsagee 
  Mine 
  have 
  

   been 
  analyzed 
  by 
  Professor 
  Genth, 
  M. 
  Chatard, 
  and 
  Dr. 
  Koenig, 
  the 
  

   results 
  obtained 
  by 
  these 
  chemists 
  are 
  given 
  below 
  : 
  — 
  

  

  