﻿L. 
  V. 
  Pirsson 
  — 
  Mineralogical 
  Notes. 
  407 
  

  

  2. 
  Hematite 
  and 
  Oassiterite. 
  — 
  Interesting 
  specimens 
  of 
  hem- 
  

   atite 
  and 
  cassiterite 
  intimately 
  associated 
  and 
  crystallized 
  have 
  

   been 
  forwarded 
  by 
  Prof. 
  F. 
  A. 
  Genth 
  for 
  crystallographic 
  ex- 
  

   amination. 
  The 
  place 
  from 
  which 
  they 
  come 
  is 
  Mina 
  del 
  

   Diablo, 
  Durango, 
  Mexico. 
  Among 
  them 
  a 
  number 
  of 
  un- 
  

   doubted 
  pseudomorphs 
  of 
  cassiterite 
  after 
  hematite 
  were 
  ob- 
  

   served. 
  They 
  are 
  too 
  small 
  and 
  lusterless 
  for 
  the 
  forms 
  to 
  be 
  

   determined, 
  but 
  the 
  whole 
  grouping 
  is 
  precisely 
  the 
  same 
  as 
  

   that 
  of 
  hematite 
  in 
  the 
  familiar 
  "Eisenrose" 
  habit, 
  consisting 
  

   of 
  radiating 
  plates. 
  Often 
  the 
  central 
  portion 
  of 
  these 
  plates 
  

   consists 
  of 
  a 
  piece 
  of 
  hematite, 
  the 
  outer 
  surrounding 
  part 
  of 
  

   tin 
  oxide. 
  There 
  were 
  also 
  seen 
  pseudomorphs 
  of 
  cassiterite 
  

   after 
  some 
  octahedral 
  mineral, 
  probably 
  magnetite. 
  

  

  These 
  occurrences 
  of 
  cassiterite 
  and 
  

   hematite 
  have 
  already 
  been 
  described 
  

   by 
  Genth 
  and 
  vom 
  Rath,* 
  but 
  in 
  

   these 
  specimens 
  lately 
  examined 
  an 
  

   additional 
  point 
  of 
  interest 
  was 
  noted. 
  

   This 
  is 
  the 
  presence 
  of 
  cellular 
  crys- 
  

   tals 
  of 
  hematite 
  filled 
  with 
  cassiterite. 
  

   One 
  of 
  these 
  is 
  shown 
  in 
  fig. 
  4. 
  The 
  

   forms 
  present 
  on 
  this 
  crystal 
  are 
  

  

  c, 
  0001, 
  0; 
  a, 
  1120, 
  i-2; 
  r, 
  1011, 
  R; 
  7, 
  Oil], 
  -1; 
  s, 
  0221, 
  -2; 
  n, 
  2243, 
  f-2; 
  

   d, 
  1012, 
  i; 
  9, 
  2021, 
  2. 
  

  

  Those 
  chiefly 
  developed 
  are 
  the 
  prisms 
  and 
  the 
  basal 
  pinacoids 
  

   which 
  give 
  the 
  crystals 
  its 
  habit. 
  In 
  reality 
  these 
  faces 
  are 
  

   present 
  to 
  a 
  considerable 
  degree 
  only 
  along 
  the 
  edges, 
  the 
  re- 
  

   maining 
  parts 
  being 
  sunken 
  and 
  filled 
  with 
  a 
  roughened 
  surface 
  

   of 
  cassiterite 
  which 
  runs 
  on 
  through 
  the 
  crystal. 
  The 
  polish 
  

   and 
  luster 
  of 
  as 
  much 
  of 
  the 
  face 
  as 
  is 
  present 
  is, 
  however, 
  

   very 
  fine 
  and 
  brilliant 
  

  

  A 
  thin 
  section 
  of 
  this 
  individual 
  was 
  prepared 
  parallel 
  to 
  

   the 
  unit 
  prism 
  to 
  ascertain 
  if 
  the 
  cassiterite 
  had 
  here 
  also 
  any 
  

   definite 
  orientation 
  in 
  regard 
  to 
  the 
  hematite. 
  None 
  was 
  ob- 
  

   served. 
  The 
  two 
  minerals, 
  both 
  appearing 
  fresh 
  and 
  unaltered, 
  

   were 
  present 
  in 
  irregularly 
  mingled 
  masses. 
  The 
  cassiterite 
  

   was 
  formed 
  of 
  an 
  intimate 
  crystal 
  aggregation 
  as 
  shown 
  by 
  its 
  

   slight 
  but 
  uniform 
  action 
  on 
  polarized 
  light. 
  

  

  From 
  these 
  facts 
  it 
  would 
  seem 
  as 
  if 
  the 
  two 
  minerals 
  had 
  

   been 
  formed 
  simultaneously 
  and 
  the 
  hematite 
  having 
  a 
  greater 
  

   tendency 
  to 
  crystallize 
  than 
  the 
  cassiterite 
  had 
  assumed 
  its 
  

   crystal 
  boundaries 
  without 
  regard 
  to 
  the 
  latter. 
  

  

  3. 
  Gypsum. 
  — 
  The 
  crystals 
  which 
  are 
  illustrated 
  in 
  fig. 
  5 
  are 
  

   from 
  Girgenti, 
  in 
  Sicily, 
  and 
  are 
  now 
  in 
  the 
  cabinet 
  of 
  Prof. 
  

   Geo. 
  J. 
  Brush. 
  They 
  are 
  twinned 
  according 
  to 
  the 
  usual 
  method, 
  

  

  * 
  Proceedings 
  Am. 
  Phil. 
  Soc, 
  1887, 
  xxiv, 
  23. 
  

   Am. 
  Jour. 
  Sci. 
  — 
  Third 
  Series, 
  Yol. 
  XLII, 
  No. 
  251. 
  — 
  Notember, 
  1891. 
  

  

  28 
  

  

  