﻿394 
  J. 
  B. 
  Umpleby, 
  etc. 
  — 
  Custer 
  ite 
  : 
  A 
  New 
  Mineral. 
  

  

  Cuspidine 
  

   Theoretic 
  fluo- 
  

   hillebrandite 
  

   Custerite 
  

  

  Ca.Si.F.0,. 
  

   Ca.Si.F.0. 
  ■ 
  

  

  unstable, 
  non-existent. 
  

  

  — 
  Ca 
  4 
  Si 
  2 
  F 
  2 
  (OH) 
  2 
  6 
  , 
  dimorphous 
  : 
  (1) 
  orthorhom- 
  

   bic 
  form 
  isomorphous 
  with 
  hillebrandite 
  (not 
  

   known) 
  and 
  (2) 
  monoclinic. 
  

  

  Hillebrandite 
  — 
  Ca 
  4 
  Si 
  2 
  (OH) 
  4 
  6 
  , 
  dimorphous: 
  (1) 
  monoclinic 
  form 
  

   isomorphous 
  with 
  custerite 
  (not 
  known) 
  and 
  

   (2) 
  orthorhombic. 
  

  

  Zeophyllite 
  — 
  Ca 
  4 
  Si 
  3 
  H 
  4 
  F 
  2 
  O 
  n 
  , 
  dimorphous, 
  the 
  known 
  form 
  

   not 
  related 
  to 
  the 
  above 
  named 
  minerals. 
  

  

  The 
  close 
  chemical 
  relationship 
  of 
  these 
  four 
  minerals 
  can 
  be 
  

   shown 
  by 
  writing 
  their 
  formulas 
  so 
  as 
  to 
  keep 
  intact 
  the 
  com- 
  

   mon 
  compound, 
  Ca 
  4 
  Si 
  2 
  F 
  2 
  7 
  . 
  

   Cuspidine 
  = 
  Ca 
  4 
  Si 
  2 
  F 
  2 
  7 
  . 
  

  

  Custerite 
  = 
  Ca 
  4 
  Si 
  2 
  F 
  2 
  7 
  . 
  H 
  2 
  (or 
  cuspidine 
  plus 
  water). 
  

   Hillebrandite 
  = 
  Ca 
  4 
  Si 
  2 
  (OH) 
  2 
  7 
  .H 
  2 
  0. 
  

  

  Zeophyllite 
  = 
  Ca 
  4 
  Si 
  2 
  F 
  2 
  7 
  . 
  H 
  2 
  . 
  Si0 
  2 
  (or 
  cuspidine 
  plus 
  

   water 
  and 
  silica). 
  

  

  These 
  relations 
  suggest 
  many 
  things 
  — 
  the 
  existence 
  of 
  a 
  

   hydroxy-cuspidine, 
  Ca 
  4 
  Si 
  2 
  (OH) 
  2 
  7 
  ; 
  the 
  derivability 
  of 
  custerite 
  

   and 
  zeophyllite 
  (or 
  a 
  polymorphic 
  form 
  of 
  the 
  zeophyllite 
  com- 
  

   pound) 
  from 
  cuspidine 
  by 
  the 
  actual 
  addition 
  of 
  water 
  and 
  

   silica, 
  etc. 
  

  

  The 
  essential 
  properties 
  of 
  the 
  four 
  minerals 
  considered 
  in 
  

   the 
  preceding 
  paragraphs 
  are 
  briefly 
  tabulated 
  below 
  for 
  pur- 
  

   poses 
  of 
  future 
  reference. 
  

  

  Properties 
  of 
  Custerite 
  and 
  related 
  minerals. 
  

  

  

  Custerite. 
  

  

  Zeophyllite. 
  

  

  Cuspidine. 
  

  

  Hillebrandite. 
  

  

  Composition 
  

  

  Ca 
  4 
  Si 
  2 
  H 
  2 
  F 
  2 
  8 
  

  

  Ca 
  4 
  Si 
  3 
  H 
  4 
  F 
  2 
  O 
  n 
  

  

  Ca 
  4 
  Si 
  2 
  F 
  2 
  7 
  

  

  Ca 
  4 
  Si 
  2 
  H 
  4 
  O 
  10 
  

  

  Symmetry- 
  

  

  Monoclinic 
  

  

  Khombohedral 
  

  

  Monoclinic 
  

  

  Orthorhombic 
  

  

  Cleavage 
  

  

  Two, 
  basal 
  and 
  

   prismatic 
  

  

  One, 
  basal 
  

  

  One, 
  basal 
  

  

  Prismatic 
  (?) 
  

  

  Hardness 
  

  

  5-6 
  

  

  3 
  

  

  5-6 
  

  

  5-6 
  

  

  Density 
  

  

  2-91 
  

  

  2-75 
  

  

  2-97 
  

  

  2-69 
  

  

  Fusibility 
  

  

  Difficult 
  

  

  Very 
  easy 
  

  

  Difficult 
  

  

  Difficult 
  

  

  Axial 
  plane 
  

  

  Normal 
  to 
  basal 
  

  

  Normal 
  to 
  

  

  {010}, 
  normal 
  

  

  Parallel 
  to 
  

  

  

  cleavage 
  

  

  cleavage 
  

  

  to 
  cleavage 
  

  

  cleavage 
  

  

  Index 
  y 
  

  

  1 
  598 
  

  

  1-55 
  

  

  

  1-612 
  

  

  Index 
  (3 
  

  

  1-589 
  

  

  

  

  

  Index 
  a 
  

  

  1-586 
  

  

  

  

  1-605 
  

  

  Birefringence 
  

  

  o-oii 
  

  

  

  

  •007 
  

  

  2E 
  

  

  105° 
  

  

  0-27i° 
  

  

  iio° 
  

  

  60-80° 
  

  

  Dispersion 
  

  

  Strong, 
  p 
  > 
  v 
  

  

  p 
  < 
  v 
  

  

  Crossed, 
  very 
  

   distinct, 
  p 
  >v 
  

  

  p 
  ; 
  < 
  V 
  

  

  Sign 
  

  

  Positive 
  

  

  Negative 
  

  

  

  Negative 
  

  

  Extinction 
  

  

  6i° 
  

  

  

  5° 
  

  

  0° 
  

  

  Twinning 
  

  

  Prominent, 
  

   polysynthetic 
  

  

  

  Tw. 
  pi. 
  (100) 
  

  

  

  Elongation 
  

  

  

  

  

  Z 
  

  

  