﻿Penfield 
  and 
  Warren 
  — 
  Minerals 
  from 
  FranMin^ 
  N. 
  J. 
  343 
  

  

  after 
  fusion 
  it 
  dissolves 
  and 
  yields 
  gelatinous 
  silica 
  upon 
  evapo- 
  

   ration. 
  In 
  the 
  closed 
  tube, 
  at 
  a 
  high 
  temperature, 
  a 
  little 
  

   water 
  is 
  given 
  off. 
  

  

  A 
  considerable 
  quantity 
  of 
  hancockite 
  was 
  taken 
  from 
  the 
  

   mine 
  at 
  one 
  time, 
  and 
  it 
  is 
  the 
  most 
  abundant 
  of 
  the 
  new 
  

   species 
  described 
  in 
  this 
  paper. 
  It 
  is 
  named 
  after 
  Mr. 
  E. 
  P. 
  

   Hancock 
  of 
  Burlington, 
  N. 
  J. 
  

  

  2. 
  Glaucochroite. 
  

  

  This 
  mineral 
  was 
  collected 
  by 
  S. 
  L. 
  Penfield 
  in 
  September, 
  

   1898, 
  and 
  was 
  subsequently 
  sent 
  to 
  New 
  Haven 
  for 
  identifica- 
  

   tion 
  by 
  Mr. 
  W. 
  M. 
  Foote, 
  who 
  had 
  collected 
  several 
  specimens 
  

   of 
  it 
  earlier 
  in 
  the 
  season. 
  It 
  occurs 
  in 
  prismatic 
  crystals 
  be- 
  

   longing 
  to 
  the 
  orthorhombic 
  system, 
  and 
  in 
  columnar 
  aggregates 
  

   imbedded 
  in 
  a 
  white 
  matrix. 
  The 
  largest 
  crystals 
  thus 
  far 
  

   observed 
  do 
  not 
  average 
  over 
  2™"" 
  in 
  greatest 
  diameter, 
  while 
  

   the 
  length 
  of 
  some 
  of 
  the 
  columnar 
  aggregates 
  somewhat 
  

   exceeds 
  10"°^. 
  

  

  Isolated 
  crystals 
  generally 
  show 
  the 
  form 
  of 
  a 
  prism 
  m 
  (110), 
  

   sometimes 
  in 
  combination 
  with 
  a 
  second 
  prism 
  s 
  (120), 
  and 
  thus 
  

   far 
  all 
  attempts 
  to 
  find 
  a 
  crystal 
  with 
  terminal 
  faces 
  have 
  proved 
  

   unsuccessful. 
  A 
  few 
  penetration 
  and 
  contact 
  twins 
  have 
  been 
  

   observed, 
  the 
  twinning 
  plane 
  being 
  the 
  brachydome 
  (Oil), 
  and 
  

  

  the 
  vertical 
  axes 
  of 
  the 
  individuals 
  crossing 
  at 
  angles 
  of 
  about 
  

   60° 
  and 
  120°. 
  Fig. 
  2 
  is 
  an 
  illustration 
  of 
  one 
  of 
  these 
  penetra- 
  

   tion 
  twins, 
  drawn 
  with 
  the 
  camera 
  lucida 
  as 
  it 
  appeared 
  under 
  

   the 
  microscope. 
  On 
  the 
  twin 
  crystals 
  the 
  pinacoid 
  a 
  (100) 
  is 
  

   generally 
  developed, 
  although 
  it 
  was 
  not 
  observed 
  on 
  any 
  of 
  

   the 
  simple 
  crystals. 
  

  

  The 
  prismatic 
  faces, 
  although 
  bright, 
  were 
  vicinal, 
  and 
  con- 
  

   sequently 
  it 
  was 
  difficult 
  to 
  obtain 
  reliable 
  measurements 
  of 
  the 
  

   prismatic 
  angle. 
  The 
  average 
  of 
  a 
  number 
  of 
  measurements 
  

  

  